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Marine Biological Laboratory 

,.r..,.A J^y 51, 1941 

Accession No. '^5622 

Gven By "^^^ Hacnlllan Go. 

Place He- rork City 






All rights reserved 







M.A., Sc.D., Hon. Sc.D. (Harvard), F.R.S. 

European Correspondent, late Director, Botanic 
Gardens, Rio de Janeiro 







page vii 

Chapter I. The Coming of the Darwinian Theory of 

Natural Selection 1 

II. Contacts with Darwinism (i). The Podo- 

stemaceae g 

III. Contacts with Darwinism (ii). Endemism, 

Age and Area 24 

IV. The Hollow Curve 33 
V. Contacts with Darwinism (iii). Mutation 43 

VI. Contacts with Darwinism (iv). Adaptation 52 

VII. Isolation q\ 

VIII. Differentiation 65 

IX. Divergence of Variation 74 

X. Some Test Cases between the Rival Theories. 

A. Numerical gg 

XI. Some Test Cases between the Rival Theories. 

B. Morphological I03 

XII. Some Test Cases between the Rival Theories. 

C. Taxonomic 132 

XIII. Some Test Cases between the Rival Theories. 

D. Geographical Distribution 142 

XIV. General Discussion lg4 
XV. Final Summary of Conclusions 191 

Appendices I94 

References to Literature 200 






/Vn accident in 1905, and the nature of my official occupation, 
forced me to work that could be done in spare time with the 
aid of a pen and a library, and since then I have largely devoted 
myself to the study of geographical distribution. The dictionary 
for which I was responsible emphasised in my mind the enormous 
variety in sizes and distribution of families, genera, and species. 
All seemed a nearly hopeless confusion. Yet this is not nature's 
way; her work is always beautifully planned, as Darwin had 
already shown in the wonderful theory of evolution, whose 
establishment as a working guide through the intricacies of life 
was due to him, and gave hiin his lasting claim to fame. Without 
a mechanism to operate it, however, few were prepared to make 
so great a break with what had gone before. In natural selection, 
Darwin produced an apparently serviceable mechanism, which 
was so familiar to every one that it had a great appeal, soon 
resulting in the establishment of evolution in an unassailable 
position. But during the last fifty years there has always been 
an underlying feeling that all was not well -sWth natural selection. 
The writer, though brought up in its strictest school, soon began 
to feel very doubtful about it, and a few years of experience with 
tropical vegetation made him realise that selection could not be 
responsible for evolution. From that time onwards he has never 
ceased to bring up objections to it, though rarely has any answer 
to these been attempted. Selection is now no longer required as 
a support for evolution, and must take its proper place, which is 
one of great importance, as has been pointed out here and 

The writer then set out, some thirty-five years ago, to find 
some definite laws underlying the welter of facts in distribution. 
The first thing that really set him upon the track was the 
discovery in 1912 of the "hollow curve" formed by the numbers 
of species in the genera of the Ceylon flora, a curve which soon 
proved to be universal in both floras and faunas. This led to the 
development of the theory set out in Age and Area in 1922. 
Being, among other things, a flat contradiction of the theory of 
gradual adaptation through the agency of natural selection, this 
theory of age and area was not accepted, but as the counter 


arguments brought up mostly assumed that the older theory was 
sound, the writer's faith remained unchanged, and he continued 
to follow up his beliefs. They are now yielding interesting results, 
of which the present book is one, while another, dealing with 
distribution, and whichis perhaps even more subversive of current 
opinions (used as a shelter for so much in national policies), is 
upon the road to completion. 

The present book, the logical sequence of Age and Area, has 
been greatly delayed by various inconveniences, and by the great 
quantity of statistical work required. This was so great a burden 
that I can hardly sufficiently express my gratitude to my friend 
Mr John Murray, late of the Indian Educational Department, 
who undertook a great deal of it, and with his trained mathe- 
matical skill was able to do it well and rapidly. I am also deeply 
indebted for aid to Dr W. Robyns, Director of the Botanic 
Garden at Brussels, Dr B. P. G. Hochreutiner, Director of that 
at Geneva, and Sir Arthur Hill, Director of that at Kew, at all 
of which places, and especially the first named, I have done 
much work. My friend Mr G. Udny Yule has helped me very 
greatly with criticism and assistance, and I am also much indebted 
for help to Mr J. S. Bliss, Dr C. Balfour Stewart, and many 




25 March, 1940 

tif |LI3RAR^ 



J\s a recent product of evolution, man must have arrived upon 
the scene to find himself in a world that was already well pro- 
vided with animals and with plants. Some animals would be 
actively hostile and dangerous to him, some would be afraid of 
him, some would be indifferent; some plants would be poisonous, 
some good to eat or to provide useful materials, some indifferent. 
Man would presumably inherit some notion of what to eat, and 
how to obtain it, but it is clear that in his early days the struggle 
for existence must have been severe, especially if one remembers 
the prolonged infancy and helplessness of his offspring. He 
probably had greater brain power, and may have had some 
leanings towards co-operation, otherwise chiefly showTi by insects. 
Whilst failure in the struggle for existence at the very beginning 
would probably have meant his complete extermination, the risk 
would lessen as he established himself in various different places 
removed from that in which he probably began. It is an intriguing 
thought that he may owe his first survival to having arisen in 
some place not troubled by dangerous animals, or to some other 
stroke of what seems like mere luck. 

From verv earlv times he must have been struck by the bodily 
likenesses of many of the organisms by which he was surrounded. 
He would soon recognise the difference between the male and the 
female of the same species, and he would distinguish, for example, 
between the tiger, the leopard, and the cat, or between the wolf, 
the fox, and the dog. He would see the evident likenesses that 
run through these triads, and that it was greater between tiger 
and cat than between tiger and dog. He would see other like- 
nesses between goose, duck, and swan, between owl, eagle and 
hawk, or yet again between lizard, snake, and crocodile. But he 
would also notice that there were overriding distinctions among 
these various animals — that both the cat group and the dog 
group could be included in a greater group that we now call the 
Mammals, the eagle group and the duck group in the greater 
group of Birds, and so on. Thus there would grow up the notion 
of groups within groups, which is the essence of all classification. 



The likenesses between plants are often less immediately 
obvious, and as compared with animals they seem to have been 
less remarked mitil a few centuries ago. One may see this lack of 
observation upon the part of mankind in the common names 
of plants, which are often old. Thus one often finds such names 
as meadow-rue, marsh-marigold, rock-rose, sea-heath, wood- 
sorrel, and the like, applied to plants that are in no way closely 
related to the rue, the marigold, the rose, the heath, or the sorrel, 
though they may have a superficial likeness in the leaves, in the 
look of the flowers, in their colour, or in the taste. But at the 
same time, one must also notice that many plants belonging to 
the same families (as now recognised) have similar names. Thus 
many Cruciferae, with their cress-like taste (cress itself is a 
member of the family), have names like bitter-, penny-, rock-, 
thale-, wart-, water-, winter-, and yellow-cress. The same taste, 
however, occurring in the seeds of the garden Tropaeolum, that 
plant used to be known as Indian cress, though it belonged to a 
totally different family. This also illustrates the now familiar fact 
that to place an organism in its proper relationships one must not 
rely upon a single character only. The name vetch is common 
among the British Leguminosae, and grass among the Gramineae, 
though here again one finds members of other families, often 
unrelated to the grasses, known as arrow-, cotton-, eel-, goose-, 
knot-, scorpion-, scurvy-, and whitlow-grass, because of some 
resemblance in habit, leaves, or other things. 

Gradually the true likenesses of plants began to be recognised 
to such an extent that they were grouped into species and 
genera within families, and these again within larger groups, 
especially by the work of Tournefort, Linnaeus, Jussieu, Brown, 
Endlicher, and many others of more recent date, so that now 
we have what is probably a reasonably good classification of 

Till about a century ago, the universally accepted view of the 
origin of plants and animals was that they had been specially 
created, each species in the form in which it now appears upon the 
earth, whilst their varieties were formed later, as the areas 
occupied by the species became larger or more varied. But it was 
clear that though one might group together the buttercup family, 
or the cat family, special creation would not explain, though it 
made the need of explanation greater, why they should possess 
such likenesses as caused them to be thus grouped together. 
Since the time of Aristotle vague ideas had been floating about. 


that such groups might owe their origin and their likeness to 
descent from some common parent, accompanied by such modi- 
fication in different directions that there would arise forms like 
the wolf and the dog, or the apple and the pear, showing an 
obvious family resemblance though differing in detail. But 
owing to the lack of any mechanism that seemed in any way 
capable of bringing it about, this idea of "evolution" was not 
seriously taken up, except by a few like Lamarck and St Hilaire, 
and never became what one may term practical politics until the 
coming in 1859 of Charles Darwin's famous book ^'The Origin of 
Species by means of Natural Selection, or the Preservation of 
Favoured Races in the Struggle for Life", preceded, on 1 July 
1858, by a joint paper by Darwin and by Alfred Russel Wallace, 
an independent discoverer, read at the Linnean Society. Both 
writers had been more or less inspired by reading Malthus (30) 
to realise the struggle for existence that must always be going on 
wherever living beings occur, a struggle which becomes the 
fiercer the more that thev are crowded together, as for instance 
at the birth of young, or of germination of seeds, for it is well 
known that both animals and plants tend to produce more off- 
spring than there is room for. Though by the aid of wind, water, 
animals, etc. the seed may be scattered to some extent, the chief 
crowd will always tend to be near together, and the great struggle 
will be among the seedlings, rather than between them and the 
parent, against which they will usually have but little chance. 
As there will generallv be too manv seedlincrs for the available 
space, the struggle will be severe, even if the competitors be 
connected with the parent by an offshoot or runner. The survivors 
will largely be chosen by chance, for early arrival on the spot, a 
less shady or better watered position, a better or softer patch of 
soil, and so on, will all be of greater advantage to the young 
seedling than any advantage that it may carry in itself as com- 
pared with its competitors of the same species, just as in the 
human struggle for existence parental advantage, the right school 
tie, etc. are of value. If it finds itself late in germination, upon 
poor soil, in a place with insufficient water, and so on, natural 
selection or competition will kill it out, inasmuch as it is unsuited 
to the conditions with which it has met, even though it may be 
suited well enough to what one may call the normal conditions of 
the place. It may also be killed out if it be the offspring of parents 
that have been used to somewhat different conditions, for it will 
probably carry with it their suitability to conditions. The more 



like those from which it came that the conditions are, the better 
chance will the young plant have, whereas if it come from some 
distance, where the conditions are likely to be somewhat dif- 
ferent, it will be more a matter of good luck should it succeed in 
establishing itself in the new locality. 

As competitors begin to decrease, the struggle for existence 
will probably become somewhat less intense. When mature, the 
struggle will be largely that to secure the most of any small space 
for expansion of roots or of leaves that may become vacant. 

Seeing a struggle like this, it seems natural to suppose that if 
any of the youngsters possessed any character that might give it 
any advantage against the rest, however slight, it would tend to 
win in the struggle more often than not. It is a remarkable thing 
that inasmuch as evolution is only clearly shown in structural 
characters, and natural selection was trying to explain evolution, 
it ignored the functional characters, and tried to explain the 
structural ones. But of course if the functional characters had 
been the only ones that were acted upon, there would have been 
little to show that any evolution had gone on at all. There would 
obviously be no need for all the structural differences. 

Assuming that the advantageous character were inherited, 
another plant might win in the next generation, and so on, the 
character perhaps (another assumption) becoming more and 
more marked in each generation until at last, when taken 
together with other characters that had also varied (whether in 
correlation with the first, or also under the influence of selection), 
a specific difference was arrived at, and a new species would have 
been formed. As this would have been formed by a definite 
adjustment to the local conditions, it would be what is usually 
called adapted to them ; this type of adaptation we shall call in 
future structural adaptation, as it was in structure that the 
changes were supposed to show that had brought the advantages 
with them. As it would tend to be the unimproved offspring of 
the old species, which retained its specific characters, that would 
be defeated in the struggle for existence, the old species would 
thus tend to decrease in numbers, being gradually reduced to the 
rank of a small and local group of plants, which might be looked 
upon as a relic of former vegetation, and which in time would die 
out altogether. And, supposing the original species to be found 
upon a considerable area, where there might be differences in 
conditions between different parts, then it might vary in two or 
more directions, giving rise to two or more species. In this case 


the old species would tend to become discontinuous in its distri- 
bution by being replaced in some of its area by the new ones. 

On the face of it, this suggested mechanism for the carrying on 
of evolution, to which Darwin gave the name of Natural Selection 
("or the preservation of favoured races in the struggle for life") 
seemed eminentlv reasonable, and one that could do the work 
required. But the struggle was necessarily of each individual of a 
species for itself alone, and if one individual showed a favourable 
variation while its neighbours did not, the variation would soon 
tend to be lost by crossing. This was shown by Fleeming 
Jenkin (21) in a criticism which Darwin considered as the best 
that was ever made of his work. It therefore became necessary to 
stipulate for the same variation to appear in many more or less 
adjacent individuals of the species, scattered as a rule over a 
considerable area. Crossing would then be useful, rather than 
injurious. This in turn meant that the variation must probably 
have been controlled, directlv or indirectlv. bv the external con- 
ditions, and these would most likely be those of climate or of soil, 
for the biological conditions largely depend upon which particular 
plants may happen to surround the individual concerned at any 
given place. 

Instead of an external force, there might of course have been 
some compelling internal force which made a whole lot of indi- 
viduals vary in the same way, and in this case one would certainly 
expect all to vary. Whether the force were external or internal, 
unless all varied alike over a considerable area, the advantage 
would be lost by crossing. In either case, it is a little difficult to 
see where natural selection got any leverage, for there would be 
no competition between the new and the old, except at the margin 
between them, where the new would in any case tend to be lost 
by crossing. When Darwin gave way, as he was forced to do, to 
this criticism of Fleeming Jenkin, the freedom of the natural 
selection theory was really lost. 

The struggle for existence, felt as it was in every community 
and family, was such a commonplace of everyday life, that the 
principle had a very great psychological appeal, and was soon 
taken up on all hands. The long neglected theory of evolution 
rose "in the attitude of claimant to the throne of the world of 
thought, from the limbo of hated, and as many hoped, of for- 
gotten things " (66). Rarely has any h\^othesis met with greater 
success than did natural selection. A mechanism familiar to 
everyone seemed able to operate the long wished for process of 


evolution. Every man felt, as Mrs Arber has said, that he was 
one of those picked out by it, and so he felt it his duty to support 
the theory. Though Darwin's immortal service was really the 
establishment of evolution, the name Darwinism became 
attached rather to the theory of natural selection, which became 
a cult, and which now exercises enormous influence in the world 
at large, even national policies being in some instances largely 
tinged with it. This is another instance of the influence of the 
dead hand, so well brought out by Woolf in After the Deluge, 
chap. I. 

Evolution itself is now so well established that it has no longer 
any need whatever for any assistance or support from the hypo- 
thesis of natural selection, and whether the latter be true or not 
matters little or nothing. What we have to do is to follow up the 
theory of evolution, and find out something more about its 

Natural selection was a new theory that was a complete 
reversal of the old. Instead of being created suddenly, so that 
at once thev showed all their differences, which are often con- 
siderable, and usually more or less discontinuous, living beings 
were formed gradually by the selection and accumulation of small 
diff'erences that gave some advantage to their possessors in the 
struggle for existence that was a daily commonplace of life. 
Creation in its usual sense was replaced by evolution, and the 
appearance of larger differences by the accumulation of smaller. 
The family resemblances that were mentioned above were now 
explained, thus removing to a period immensely farther back the 
conception that the phenomena of the life of animals and plants 
were pre-ordained, and throwing open to research a vast field of 

With natural selection itself, time has dealt less kindly. It 
acquired an immense prestige by its success in establishing 
evolution, but has not proved so useful in the further advance of 
science as was expected. It contains too many assumptions, and 
has required too many supplementary hypotheses to enable it to 
offer sure ground upon which to build, and is ceasing to be in- 
voked as it used to be. It was at one time known as the doctrine 
of "nature red in tooth and claw", and as such has become 
largely incorporated into the theory of life that underlies the 
general policies of the world. 

At the time of its greatest success, a rival, pre-Darwinian, 
system of evolution, known by the name of Differentiation, was 


in process of development, and was being pushed by the famous 
zoologists Owen and Mivart. It must be admitted that against 
the psychological appeal of "Darwinism" it had no chance, but 
at the same time, there was even then much truth underlying it, 
and as time has gone on people are becoming more and more 
inclined to think that in some respects at any rate it will give a 
closer approach to the truth than will selection, the absolute need 
for which as a support for evolution has now passed by. Special 
creation went too far in one direction, natural selection in the 
other, and differentiation may be called a kind of compromise. 



i-T is not intended here to write a history of the movement known 
as Darwinism, but rather to sketch the author's contacts with it, 
which have lasted for fifty years. 

The pubh cation of the Origin of Species created a revolution in 
the world of science, but like most great changes in ways of 
thought it was very unwelcome to the older men, who rarely 
came round so far as to accept it in any whole-hearted way. In 
the next few vears there was a flood of ant i -Darwinian literature, 
and many incisive criticisms were made upon natural selection 
(rather than upon evolution) from one of which we quote the 
next sentence: "It follows, therefore, that if we accept the 
Evolutionists' view, every specialised chemical compound met 
with in some living beings only must fulfil the condition, that 
every approximation to the complete compound must have 
been of advantage to the being in which it was produced in the 
struggle for life. . .unless these very substances existed in, and 
formed points of difference between, Mr Darwin's few original 
forms" (29, p. 134). Maclaren also points out that change of 
climate does not change the chemistry of a plant, so that there 
is no opening for natural selection in a change of conditions. 

It was clear that there must be discontinuity in evolution, 
and this was difficult to harmonise with the view that it had 
proceeded by gradual accumulation of minute steps. Chemical 
substances of differing nature could not be formed from one 
another by slow and gradual steps, nor could gradual steps in the 
formation of such a substance as the green colouring matter of 
plants (chlorophyll), for example, be of value. Yet this, probably 
one of the early formed organic substances, providing the food 
for plants and animals alike, ranks with water and protoplasm 
among the most important chemical substances in the world. 

The writer has been chiefly occupied with economic botany for 
over forty years, and to him these considerations have long been 
a fatal objection to the current theory of evolution — the gradual 
passage, by reason of improving structural adaptation to the 
surrounding conditions of life, from small variations through 


larger to well-marked varieties, to species, and to higher forms. 
There is no inherent reason why economic botany should remain 
what it now is, an ever-increasing mass of facts with little or no 
co-ordination. What little of this there is, as may be seen at once 
by consulting Wiesner's standard treatise, is very largely 
confined to such observations as that a and h, belonging to the 
same family, produce similar economic products. This alone 
shows that the facts of economic botany must be explicable upon 
evolutionary lines. Yet, with the exception of the theory that 
poisonous plants have evolved the poison as a protection against 
animals, natural selection has never attempted to explain any- 
thing in the realm of economic botany, which ought by this time 
to be a properly classified scientific discipline, with general 
principles running through it. One chemical fact must follow 
from another. 

Something the same may be said of geographical distribution, 
which has been a favourite study of the author for the last thirty- 
five years. This again consists of a stupendous mass of facts, 
connected together by little more than a tissue of speculation. 
Sir Joseph Hooker, its great leader of former days, wrote: "All 
seem to dread the making Botanical Geography too exact a 
science; they find it far easier to speculate than to employ the 
inductive process", and the position is not so very different 
even yet. It has always been admitted that any theory of the 
mechanism of evolution must stand or fall according to whether 
it can or cannot interpret the facts of distribution. The two are 
obviously and inextricably bound together and to them should 
be added the facts of economic botany. 

At first natural selection seemed to offer an explanation of 
these geographical facts, indeed so promising an explanation 
that Hooker became one of Darwin's chief lieutenants, never 
following out to their conclusions some of the lines of work upon 
which he had begun. Gradually, however, it was discovered 
that the employment of natural selection was not leading to real 
advance, and the first enthusiasm died away, leaving distribution 
in the Cinderella-like position that it still occupies. Those who 
had leanings in the direction of distributional study turned more 
and more to the rising science of ecology, known as natural history 
of plants when the author taught the beginnings of it under Sir 
Francis Darwin in 1891-4. But though ecology is all-important 
for the details of local distribution, it cannot answer the wide 
questions which are the province of geographical distribution 


properly so-called. Some new theoretical background is required, 
other than natural selection, which has proved a very broken 
reed upon which to lean. 

Those who have tried to make evolution work upon Darwinian 
lines, i.e. in the "upward " direction from minute variety through 
variety and species, and so on, have met with continually 
increasing difficulties, with some of which we now propose to deal. 

For the variations that were ultimately to form the basis of 
new species, Darwin relied principally upon the "infinitesimal" 
or continuous variation that was well kno\Mi always to be going 
on in every possible character. Thus, supposing one measured 
the length of 500 leaves from similar plants of the same species, 
one might find the average to be 25 mm. The greatest single 
number would probably be found to show this length, but there 
would be almost, if not quite, as many measuring 24 or 26 mm., 
somewhat fewer for 23 and 27 mm., and falling away more and 
more quickly, but at about the same rate on either side. Investi- 
gation gradually showed that there were definite limits to this 
kind of variation. It follows the ordinary curve of frequency 
distribution. If one cross two individuals both having a very 
high degree of the character, the average of their offspring does 
not retain that high level, but falls back, or regresses. The high 
level can only be maintained by strenuous selection in each 
generation. Further, it is also found by experience that one 
cannot, by means of selection, pass a certain maximum. This 
kind of variation, in other words, is not fully hereditary nor is it 
irreversible, like the differences that characterise species, and 
cannot be indefinitely added up without some external aid. The 
experiences of sugar beet and other breeding show this well 
enough; never can one go beyond a certain point unless, by 
hybridisation or in other ways, one introduces new factors. In 
the struggle for existence, mere chance has much too large a share 
in determining the victors to allow even the maximum to be 
reached. Thus, on this ground alone, this type of variation was 
disqualified as forming an essential part of the evolutionary 

But this is not the only difficulty that arises in trying to use 
this kind of variation, which is always linear, or up-and-down. 
A leaf may vary infinitesimally in length, or in breadth, in the 
depth of its incisions, or in the degree of number and length of its 
hairs, but it does not vary except in sudden steps in such a 
direction as that from alternate to opposite, from simple to com- 


pound, from pinnate to palmate, from dorsiventral (facing 
upwards, with different anatomy on the two sides) to isobilateral 
(facing sideways, hke Gladiolus leaves, with the same anatomy 
on both sides), from parallel veined to net veined, or in other ways 
that could be mentioned. Now variations in length and breadth 
are rarely of much importance for distinction of species, unless so 
great that there is a wide difference between the averages in the 
two cases, while the other characters that have just been men- 
tioned will be seen at once to be such as are of great importance 
in distinction between one species and another. This is another 
fatal objection to the use of this kind of variation as part of the 
mechanism of evolution. Some kind of variation was required 
that was not only inherited and irreversible, but also differen- 
tiating and not merely linear, or up-and-down. 

Another serious difficulty was the fact that species were very 
rarely distinguished from one another by a single character only. 
Usually there were from two to six characters marking them off 
from one another, some of them more variable than the rest, and 
more liable to overlap from one species to the other, so that one 
had to examine a great number of specimens of each of the 
species to be sure that their overlap was not due simply to lack 
of real difference. Thus in Cornus, to take the first genus that 
comes to hand, C. kousa and C. capitata are closely allied species. 
The key division is that the former has the calyx truncate, the 
latter 4-lobed, and the involucral bracts more or less ovate as 
against obovate. But there are so many minor points of difference 
that the description of either takes up nearly twenty lines (49). 
None of the characters afford any opening for natural selection 
to work upon, so far as can be seen, but supposing that it had 
worked upon one, were all the rest simply correlations? One could 
hardly imagine it working upon one at a time, for what would 
ensure that a should be followed by b, which was unconnected 
with it (as are the two distinguishing characters above quoted)? 
Nor could one imagine it picking out a variation that included a 
little of each of a, b, c, d, etc., when these were unconnected, 
unless they were in some way correlated.^ But if correlation were 
to be invoked to this extent, it must be the principal, though 
perhaps only passive, factor in evolution as sho^\Ti by the 
characters that distinguish its finished product. Nearly all the 

1 Cf. Origin of Species, chap, vii, first few pages, for remarks upon this 
subject. Incidentally Darwin there suggests the "somewhere" which has 
proved such a useful refuge to the defender of natural selection. 


characters must be correlations. And why did one not find, in the 
fossil records, any species that had been fossilised before this 
complicated process had been completed? 

It is clear that, on the theory of gradual adaptation, a very 
long time must be allowed to get from one species to another. 
This means that the change of conditions must go on for a long 
time also, for if a small change in structure enabled the species 
growing in one locality to survive there, there would be no urgent 
reason why they should continue to vary in the same direction, 
unless the conditions also continued to vary in the same direction 
as that in which they had begun to do so. 

Another difficulty was to understand why variations of this 
kind should usually go so far as to pass what one may call the 
rough-and-ready line of distinction between species — that they 
should be, mutuallv, more or less sterile. 

One does not find to anv serious extent in the fossil record, 
species which represent real intermediates between existing or 
fossil species. One finds rather examples of species that have 
some of the characters of one, some of another. But one does not 
find species (as from the constant occurrence of the few characters 
side by side in existing species one might expect to do) that show 
intermediate characters between alternate and opposite leaves, 
between palmate and pinnate leaves, between erect and climbing 
stems, between racemose and cymose inflorescences, between 
flowers with and without a cyclic perianth, between isomerous 
and heteromerous flowers, between imbricate, valvate, and con- 
volute aestivation, between flowers with the odd sepal posterior 
and with it anterior, between stamens in one and in more whorls, 
between anthers opening by splitting or by teeth, valves, or pores, 
between 3-locular and 4-locular ovarv, between ventral and dorsal 
raphe, between loculicidal and septicidal fruits, and so on through 
all the important structural characters. 

All these were very serious difficulties, while it had also to be 
remembered that in any case evolution could only go on if the 
needful variations in the right direction should appear, for, unless 
this should happen, it was evident that natural selection could 
do nothing. One could not imagine the "mixed" variation of 
characters a, &, c, etc., above-mentioned appearing at all, unless 
most of it was simply correlation, and if the differences had to 
appear one by one, the chance of all appearing was but small, and 
the time required would be enormous. Forty years ago it was 
clear to the writer that some form of sudden and irreversible 


variation was required, such as was supplied by de Vries' theory 
of mutation (48). 

Evolution by gradual variation thus has many difficulties in 
its path, which in the first enthusiasm of natural selection were 
passed over with little notice. Under the influence of the criticism 
of Fleeming Jenkin, it had to be admitted that all the new plants 
of a considerable area must vary more or less in the same direc- 
tion to prevent the new variation from being lost by crossing. It 
would be lost at the edge of its territory, but would presumably 
survive in the middle. The area of the parent species would thus 
tend to become more or less discontinuous. It had to be assumed 
that the parent did not vary in a favourable direction also, but 
as all variation was assumed to be structural (it could hardly 
be otherwise, as natural selection was trying to explain a 
structural evolution), it was easy to suppose that the parent could 
not vary in such a way. It also had to be assumed that the con- 
ditions continued to change for a very long time, to such an 
extent anyhow as to pass the sterility line, or a new species could 
not be formed. This new species would evidently be well adapted 
to the new conditions whose existence was responsible for its 
coming into being, but it had also to be assumed that when 
formed, or partly formed, it would then prove so suited to the 
region in which the parent was still supreme as to kill out the 
latter there also. This was a pure assumption, but was necessary 
in order to explain the spread of the newer and better-adapted 
species, which in turn was to explain their wide distribution. We 
have shown in Age and Area, p. 34, that the older species will 
probably gain continually upon the younger in rate of dispersal, 
supposing, which seems to be the case, that there is no reason 
(when they are taken in groups) why one should spread more 
rapidly than another nearly related to it. If the area to which the 
new species was ultimately to reach were very large, it was really 
rather absurd to talk of it as adapted to the whole area. It must 
have been just a case of luck that it proved so sufficiently suited 
to far-away places as to be able to establish itself there, though 
once arrived it would begin to suit itself in detail to the local 
conditions. And it must not be forgotten that early species would 
have the best chance both of rapid travel and easy settlement. 

Finally, among the difficulties of Darwinism, it was evident 
that the variations must be such that natural selection could 
work upon them when they did appear, and as to that we have 
but little evidence. 


The hypothesis of evolution by small variation has never, so to 
speak, been officially abandoned, but it has been so altered by 
supplementary hypotheses that it is hardly recognisable, and the 
theory of mutation, brought up by de Vries, has largely taken its 
place. A mutation, which when obvious is often called a sport, 
at once produces a morphological or structural character or 
characters that are definitely distinct from those which were 
found in the parent form, and not only that, but which have come 
to stay, and are (practically) irreversible. It is always possible, 
of course, though not very probable, that some later mutation 
may change them, or some of them, back again, or to something 
else. Here, then, was a hypothesis that surmounted the chief 
difficulties mentioned above, and provided hereditary variations 
that were differentiating and (practically) irreversible. 

Mutation was taken up, though slowly, as people gradually 
realised the fatal nature of the objections to linear and infinitesi- 
mal variations. Unfortunately for its speedy success, some doubt 
was thrown upon the genuinely mutational nature of the pheno- 
mena upon which it based. Some, at any rate, appeared to have 
been due to hybridisation. But in spite of this setback, mutation 
had come to stay, and we shall trace some of its history below. 
People say that a sport is not capable of succeeding by itself, but 
we do not know what would happen if it were really viable, and 
plenty of time were allowed. 

Natural selection was, of course, essentially a theory of gradual, 
progressive, and more or less continuous adaptation to sur- 
rounding conditions. It is evident that living things are suited 
to them, for if they were not they would soon be killed out in the 
struggle for existence. Some theory that will explain adaptation 
is, therefore, very desirable. It was largely because it seemed so 
capable of doing this that natural selection was so enthusiastically 
taken up. 

Each new species was formed, according to Darwin, because it 
was an adaptational improvement upon its immediate ancestor. 
Once this was fully realised, there was a great rush into the study 
of adaptation. It was taken for granted (it could hardly be 
otherwise) that as natural selection was trying to explain evolu- 
tion, which showed itself mainly in external structural characters, 
these characters must also, of necessity, be the means of expres- 
sion of adaptation. Evolution has undoubtedly gone on in 
morphological change, but as yet we are practically without any 
proof that the change also represents the adaptation that may 


have gone on. What natural selection undoubtedly does is to 
work with the individual, and to kill out, upon the whole, those 
individuals that are below the average in any species— man or 
animal or plant — but we have no proof that it works in the same 
way with species as a whole or as units, killing out one species or 
variety to make room for another, unless in particular conditions 
which are more or less local. A species a may be killed out in one 
place, because of unsuitable local conditions, whilst its rival h 
may be killed out in another, for the same reason. If structural 
differences go for anything, there must be a great adaptational 
difference between the Dicotyledons and the Monocotyledons, 
yet both grow intermingled almost everywhere, and in much the 
same proportions. There is no " monocotyledonous " mode of life 
that suits a Monocotyledon better than a Dicotyledon, yet there 
are very great structural differences between them. 

During this period, the possibility of internal, functional, or 
physiological adaptation was ignored. Yet adaptation has far 
more to do with the physiological than with the morphological 
characters, if indeed it has anything to do with the great bulk of 
these. There are very few external characters to which one can 
point as definitely physiological. The leaves, roots, stems, 
flowers, and fruit are so to a great extent, but not differences in 
these (such as palmate or pinnate leaves, or drupes and berries), 
except rarely. Adaptation to climate, which is a physiological 
difference between one form and another, is primarily a purely 
internal adaptation. To have any chance of survival, a species 
must be suited to a greater range of climate than that with which 
it perhaps began. As it migrates into new territory, it will 
probably begin to become adapted to the slight changes with 
which it may meet as it moves with (usually) very great slowness 
into slightly differing conditions. 

A vast amount of energy was put into the study of adaptation 
during the last quarter of last century, and the imagination was 
pushed to the extreme limit to find some kind of adaptational 
value in even the least important features of plants, such as a 
few hairs in the mouth of a corolla, an unpleasant smell (to some 
human beings), and innumerable other characters (cf. books of 
this period, such as 23). Unfortunately for the adaptationist and 
for the theory of natural selection, which was founded upon 
adaptation, no one was ever able to show that the important 
morphological features of plants, which showed so conspicuously 
in the characters that marked families, tribes, genera, and most 


often also the species, had any adaptational value whatever, and 
the higher that one went in the scale, from species upwards, the 
more difficult was it to find such a value. This, when one comes to 
think it over, is really a very puzzling fact — why should the 
differences become larger the higher one goes? Is the struggle for 
existence greater among the higher groups, between two families 
for example, than between two species, and between these than 
between two individuals? A glance at the table of family 
characters, given as Appendix i, will illustrate this. 

This list of the important characters that distinguish families 
from one another is after all not so very large. Each family has 
something to show under most heads. In any pair of allied 
families that may be taken, there will be mutual agreement in 
many characters, but a contrasting difference in others, one 
character of a pair being taken in preference to the other, and 
that character tending to be shown right through the family, 
though there are nearly always exceptions in the larger families, 
the number of exceptions tending to rise with the size of the 
family. Most of the pairs of characters that are given are such 
that they do not admit of intermediates, and this divergence of 
variation, as it is called, is constantly to be found in nature 
between organisms that are so alike in most of their characters 
that they are evidently allied in descent. Divergent differences 
may show between one species and the next, between one genus 
and the next, as with the berry-fruited Cucubalus in Caryo- 
phyllaceae, between one tribe, sub-family, or family and the 
next. As one goes downwards in the scale from family characters, 
one finds more and more characters coming into use, but they can 
still very often be arranged in divergent pairs. 

One does not find (usually it is impossible) intermediates be- 
tween the two characters of a pair, except in a few like superior 
and inferior ovary, where semi-inferior is possible. But to imagine 
intermediates between alternate and opposite leaves, or between 
most of the pairs given, is to ask too much of selection. These 
characters must, one would imagine, be the result of some sudden 
change, which would give one or the other. 

The individual characters are so divergent from one another in 
each pair that it is clear, as in fact has long been well enough 
known, that variation is definitely divergent. This was always, as 
Guppy has said, a worry to Darwin, for it was extraordinarily 
difficult to understand how an evolution, working "upwards" 
through the variety and species, could drop out at each stage the 


organisms necessary to make the divergence show more and more 
as one went up in the scale. As Guppy points out in Age and 
Area, p. 104, Hooker was definitely considering the idea or 
nucleus of a theory of differentiation (19, ii, 306) but "no induc- 
tive process based on Darwin's lines could have found its goal in 
a theory of centrifugal variation. . . . Huxley was in the same case. 
For he held views of the general differentiation of types, and his 
road that would lead to the discovery of the causes of evolution 
started from the Darwinian position. That road was barred to 

One cannot conceive of any of these family differences being 
formed under the influence of natural selection. One cannot even 
suggest, in any single case, which of the two characters is the 
earlier, or what advantage can be gained by one as against the 
other, or as against any possible intermediate, if such a thing 
could exist at all. One must also remember, in dealing with 
natural selection, that there must have been an enormous de- 
struction of intermediates, of which we find no fossil record of 
any note. 

The supporters of natural selection mostly (at present, that is, 
for they are apt to change over to the reverse explanation, that of 
local adaptation) look upon the small and local genera and species 
which occur in such great numbers, as being the losers in the 
struggle for existence, i.e. the relics of a former vegetation, now 
upon the way to extinction. A very remarkable thing about these 
relics, which they do not attempt to explain, is that they do not 
occur, except very rarely, in two or more different localities, with 
a wide separation. For example, there are hardly any cases 
known where they occur in two different continents, and few 
where thev are found in the interior of two different countries on 
one continent. Nor do the great majority of them belong to small 
and isolated genera, but to the large genera (cf. p. 26), which 
natural selection regards as the successes. The "relics" therefore 
must have belonged to ancestral species which must have been 
widely distributed to give rise to their present descendants. Why 
then, when in one or more regions of slightly different conditions 
new species were developed, did not the old species become dis- 
continuous in its distribution, leaving relics in several different 

Under the natural selection theory, the large genera in the big 
families, like Senecio, Ranunculus, or Poa, are supposed to have 
been the best adapted and therefore the most successful. But 

WED 2 


they are worldwide in their distribution, which must therefore 
have gone on in early times. Has natural selection been gradually 
diminishing in its effects? 

The characters given in the " family " list are very important in 
the distinctions between families, but they also appear very 
frequently in distinctions between tribes, less often between 
allied genera, and still less often between two allied species. It is 
evident, therefore, that they can be rapidly produced, and do not 
necessarily need a long and gradual evolution from species up- 
wards. It is difficult to see how this can be so, unless they can be 
the subject of single sudden changes, which as they are usually 
divergent is not difficult to imagine. 

It is very difficult to apply the Darwinian explanation, that 
distribution is due to superior adaptation, to a genus like Senecio, 
for most of its species are, compared to the genus, quite local. If 
there be any marvellous adaptation, then, to account for the 
enormous distribution, it must be generic, and no one has ever 
been able to make even a suggestion as to what it may be, or 
wherein it is shown. The generic characters are purely morpho- 
logical, with less functional adaptation even than the specific. 

The writer, as personal assistant to that best and kindest of 
men. Sir Francis Darwin, who had helped his father in so much of 
his work, was, of course, brought up in the arcana of natural 
selection, and accepted it with enthusiasm. His first research was 
upon adaptational lines, but he was not satisfied with the adap- 
tational explanation of things, and when soon afterwards, in 
1896, he went to Ceylon to succeed Dr Trimen, his views under- 
went a complete change. The leisure time of the first six years was 
devoted to a detailed study in both Ceylon and India of that 
remarkable family of water plants the Podostemaceae (51-55), 
containing about forty genera with 160 species, found in all the 
tropics, with overlap into cooler regions. All live upon the same 
substratum of water-worn rock (or anything firm, like timber, 
that may be caught in the rock) in rapidly flowing water. They 
are annuals, flowering immediately that the spathe comes above 
water in the dry season, and then dying. If accidentally laid bare 
by an unusual fall of water in the vegetative season, they soon 
die without flowering. All the food comes from the water, and 
they have no competition for place, except among themselves. 
Enormous quantities of minute seed are produced, which have no 
adaptation at all (except in Farmeria) for clinging to their place 
in the swift current. At most one in a thousand or two may be 


caught in some fragment of old plant, or in some other place 
where it can germinate. 

At the period when this study was undertaken, the Podo- 
stemaceae, with their strange look of lichens or seaweeds, their 
peculiar mode of growth, their great variety of form, were looked 
upon as obviously showing adaptation in the highest degree, and 
it was for this reason that the work was undertaken. But among 
the conclusions drawn from it was this, that apart from those 
adaptations which they showed in common with all water plants, 
such as the lack of strengthening tissues and of stomata, there 
was in them little evidence of any special adaptation whatever. 
The conditions under which they lived were the most uniform 
that it was possible to conceive — the same mode of life, no com- 
petition with other forms of life, the same substratum, the same 
light (varying from day to day with the depth of the water), the 
same temperatures, the same food, everything the same. Yet in 
spite of this, the plants showed an enormous variety of form, 
greater than that of any other family of flowering plants what- 
soever, while water plants as a rule show little variety in form, 
and have but few genera and species. Still more remarkable was 
it that their morphology diff'ered for each continent, flattened 
roots in the Old World, flattened shoots in the New, so that it was 
usually possible to say by a simple inspection what was the 
probable habitat of a species never seen before. It was hard to 
believe that natural selection, working upon structural modifica- 
tions that have never been shown to have any functional value, 
could do this. The linking genus, Podostemon itself, covers an 
immense area, including that of many of the smaller genera, and 
is less dorsiventral than they are, though all show a highly dorsi- 
ventral flower, which stands erect, and is commonly wind 
pollinated, an unexpected combination of characters for the 
selectionist to explain. 

Once these very remarkable facts were fully realised, the 
explanation that seemed much the most probable was that on the 
whole the highly dorsiventral genera were descended from Podo- 
stemon or from some form like it. It could not be the other way 
about, for the flowering plants as a rule are not dorsiventral, 
except in the structure of the leaf, and very often in the flower. 
Nor could there have been some intermediate form, for that 
would have had to be more dorsiventral than are the flowering 
plants in general. One only of the local genera, Willisia in the 
Anamalai mountains in South India, shows as much ordinary 



symmetry in its shoots as Podostemon, and as in that genus they 
grow adventitiously from a creeping root. 

The plants of this family grow in conditions of uniformity that 
can hardly be matched in any other flowering plants, but 
amongst them is included the uniform action of a force which 
cannot be escaped. Growing as they do, always upon smooth 
water-worn rock, they cannot send their roots into the substratum, 
so that the normal polarity of the young plant, which sends its 
root down and its shoot up, is completely disturbed. By no con- 
tortions can the plants grow normally, though the rock may be of 
any kind of slope. 

There was no evidence to be found that would show that 
natural selection had anything to do with the multiplicity of form 
in these plants, for all were growing under the same conditions ; 
but there was always this inescapable force urging dorsiventrality . 
Under these circumstances, though he had started out with great 
faith in adaptation and natural selection, the author became a 
convert to the theory of mutational origin of species, adopting 
from the very first the view that mutations or sudden steps might 
at times be large enough to form species at one stroke. There were 
no signs of real intermediates, yet surely here if anywhere they 
might have been expected. An ordinary plant of another family, 
growing more or less vertically upwards, would not usually come 
under the continual influence of any powerful agent which would 
tend to make its mutations go in any particular direction, but 
with the Podostemaceae they were always being pushed in the 
direction of dorsiventrality by the maximum force that nature 
was capable of exercising in that direction. The mutations of 
ordinary plants would give rise to specific differences in which 
one could see no result of any particular directing force — there 
was little or nothing to choose between them, and they were 
morphological differences, with no adaptational value. In the 
Podostemaceae, on the other hand, the mutations showed the 
result of the continual force that was acting upon them, in a 
dorsiventrality that on the whole tended to be continually more 
and more marked the more local the genus might be. But it was 
only an adaptation in the sense that moving restlessly in bed 
might be described as adapting oneself to wearing pyjamas of 
the fabric of which hairshirts were made. The dorsiventrality 
was simply a morphological feature which had been forced upon 
the plants. Upon this view, the difference in morphology between 
the American and the Asiatic forms was also easily accounted for 


by some small difference in morphology between the first parents 
in the two countries, which had the effect of urging the first 
mutations in somewhat different directions. It is, of course, true 
that natural selection might do the same with the same start, but 
it is not quite so easy to imagine. 

Any member of the family seems to be able to live without anv 
great difficulty where any other member can live (53, p. 535) 
though probably they have some preference as to speed of water, 
and one must remember that in any case this varies with the 
level of the river, being usually faster the higher the level. 
People who came with me to look at the Podostemaceae growing 
in the river near Peradeniya, when they saw the flat, closely 
adherent Lazvias or Hydrohryums, used to say "obvious adapta- 
tions to escape being carried away by the fast water". But in 
Brazil the comparatively enormous Moureras and other forms, 
3 or 4 ft. long, yet attached only at one end, lived in water that 
was going at twice the speed of that in Ceylon. 

Much or most of the evolution that had gone on, therefore, 
seemed to be completely de luxe, for there was no need for the 
new forms, nor was there any adaptational niche that would suit 
one form onlv. and not also many others. It would almost seem 
as if, in cases like this, if not perhaps in most, evolution must go 
on, whether there be any adaptational reason for it, or not. 

The explanation of the distribution of the Podostemaceae, 
as given by current theories based upon natural selection, en- 
counters some awkward difficulties. The most highly dorsiventral 
forms are the most local, i.e. they are "the relics of previous 
vegetation, defeated by the more widely distributed ones". In 
other words, the family began with extreme dorsiventrality, and 
then, so to speak, repented of it to some extent. But to become 
less dorsiventral under the constant and utmost influence of a 
force that is urging movement in the opposite direction, can 
hardly be looked upon as likely to happen under the influence of 
natural selection and the whole situation becomes an impasse. 

The phenomena sho^^^l by the Podostemaceae are almost 
exactlv matched in the allied family Tristichaceae, which has 
much the same distribution, and are also matched by the pheno- 
mena shown by the most completely parasitic plants, such as 
Rafflesiaceae or many fungi, which, though they grow in mar- 
vellously uniform conditions, none the less show important 
structural differences. 

The universality of this type of distribution, with the more 


primitive genera the more widely distributed, and the most 
highly modified the most local, taken together with other features 
shown by the Podostemaceae, made the writer realise that in 
trying to work evolution from the variety — which upon the 
theory of natural selection was an incipient species — upwards to 
species and further, we were trying to work it backwards. Once 
this fact had been fully grasped, as it was about thirty-five years 
ago, the theory of natural selection became for him a theory 
which in its youth had done a marvellous piece of work, but had 
exhausted itself in that effort, and was not likely to lead to any 
further serious advances, as indeed had already been shown in its 
breakdown in the study of adaptation in the last quarter of the 
nineteenth century. 

During the six years that this work occupied, the writer had 
frequent opportunities of visiting the tropical forest, and soon 
realised that the struggle for existence was mainly among the 
seedlings that tried to commence life upon any small spot upon 
which, owing to fall of a tree, the breaking off of a branch, or for 
other reason, there was rather more light than usual. But most 
of the seedlings were of differing species, and commonly also of 
different genera. And as never twice would the same assortment 
of seedlings have to be encountered, and never twice the same 
conditions of weather, it was impossible to see how slight varia- 
tions towards adaptational advantage could be of any use. Mere 
chance, as we have already pointed out (p. 3), must evidently be 
the chief factor in determining the survivors. Ecological adapta- 
tion to slight climatic and other changes must evidently be 
internal rather than external. It was possible, as Harland has 
suggested, that slight changes of this kind might entail some genie 
change, and these, when added up over long periods, might give 
rise to morphological mutations. But this has little or nothing 
to do with the straightforward natural selection that was 
normally accepted, and in any case is working downwards from 
above, as does differentiation. 

The fiercest struggle for existence that a plant is ever likely 
to encounter is that into which it must be thrown at its birth, 
when it will have to compete with other seedlings upon land 
already very fully occupied. Any form that is not adapted to the 
conditions in which it finds itself at that time will be remorselessly 
killed out, unless the time is short, hy reason of its unsuitahility ^ 
and that is what natural selection really means. Anything that 
is in any way handicapped — by unsuitability to the conditions, 


by anj^thing unfavourable in the spot upon which it is trying to 
grow, by mere late arrival as compared with its competitors, and 
so on, cannot survive in such a struggle, unless the handicap 
imposed by one thing is compensated by a start in some other. 
The actual winner or winners will be mainly picked out by chance, 
and will in all probability be derived from parents that are 
already living somewhere close by, and which may therefore be 
looked upon as already adapted to the climate and other condi- 
tions. In all probability this adaptation will be to a reasonably 
large range of temperature and other climatic conditions, for 
unless this were so, survival would be very improbable in most 
places. There is also reason to suppose, that if it be done slowly 
enough, a species may, as it moves slowly about the world, 
become slowly acclimatised to other conditions, for the range of 
some species is so enormous, and includes such varied condi- 
tions, that without some possibility of this kind it is difficult to 



JtIaving by this time (1902) completely thrown over natural 
selection as the chief mechanism of evolution, the author's next 
piece of work was a study of the remarkable flora of Ritigala 
mountain, lying isolated in the flat "dry" zone of Ce^don, in 
which little or no rain falls for the almost six months of 
the southwest monsoon. A note on the flora had already been 
published by Trimen (45). The mountain, over 2500 ft. high, falls 
with a steep cliff to face the south-west wind, and the summit, 
of but a few acres, receives rain during that monsoon, thus 
forming an outlier of the "wet" zone flora, which otherwise only 
begins upon the mountains about 40 miles away to the south. 

The flora of Ritigala summit, of over 100 species, contains one 
or two which are quite local to it, or endemic, in the botanical 
sense. The rest of the plants are largely to be found in the wet 
zone, but not in the intermediate country, which is at a much 
lower elevation, and is shown by geological evidence probably to 
have been dry since the Tertiary period. 

Endemism, about which the writer has published a good deal of 
work, is, it is hardly too much to say, a crucial feature upon whose 
proper explanation largely hangs niuch of the whole matter of 
evolution and of geographical distribution. The best known 
endemic of Ritigala is Coleus elongatus Trim. (46, and Plate 74), 
easily distinguished by having a calyx of five equal sepals instead 
of one of two lips, and by having a pendulous cymose inflorescence 
of five stalked flowers, in place of the sessile bunch of five flowers 
that is the usual thing in Labiatae. There also occurs upon the 
summit the closely related C. barbatns, widely distributed in 
tropical Asia and Africa, and upon the natural selection theory 
the most "successful" of all the Colei, but here growing together 
with C. elongatus the most "unsuccessful", and in the same way, 
upon open rocky places. Why was this so, upon the hypothesis of 
natural selection? No satisfactory answer could be given by its 
supporters, and they were obliged to bring in two supplementary 
hypotheses, which were mutually contradictory. Some said that 


C. elongatus was a local adaptation, i.e. a success, but if so, why- 
did it not have a different habitat from C. harhatust Others 
offered the reverse explanation, and said that it was a relic of 
previous vegetation, i.e. a failure. But again, why did it continue 
to grow in the same places as C. harhatus, the most widespread 
and successful of the Coleil Why was it not killed out? And why 
was it morphologically distinct from all other Colei, with a few 
exceptions in Africa? Had a pendulous inflorescence with stalked 
flowers given rise to a normal Labiate one, which otherwise 
characterises much of this genus of 150 species of tropical Asia 
and Africa ? And how did the calyx change from five equal teeth 
to two lips, one presenting four teeth, one one? Regular variation 
in a calyx would always affect the teeth equally; a two-lipped 
condition could only be the result of some sudden change. The 
final refuge of the natural selectionist is usually to say that the 
peculiarities must have been useful at some other time, or at 
some other place. But the conditions upon the summit of Riti- 
gala, and in all probability in the country between it and the wet 
zone, had not altered since the Tertiary, and there was no sign of 
C elongatus anywhere else, while its most successful and closely 
related rival, C. harhatus^ was upon the same summit, in similar 
places, and about equally common. Neither of the diametrically 
opposed solutions offered by the natural selectionists would hold 
water, especially as no adaptational value could possibly be read 
into either inflorescence or calyx, whereas the problem was easily 
solved by imagining C. elongatus to have arisen by a single 
mutation from C. harhatus. And why was there another endemic 
in the mountain mass of the wet zone also? Was it a case of 
isolation resulting in a new species upon Ritigala? This was the 
only probable explanation other than that of mutation which has 
been offered, and as the wet-zone endemic has neither the equal 
sepals nor the pendulous inflorescence, marked mutation must 
have gone on. There was no opening for natural selection, even 
could it have produced such differences among the few dozen 
plants of both species upon the summit of Ritigala. It was also 
clear that upon the principles of natural selection, as altered by 
Darwin after the destructive criticisms of Fleeming Jenkin (21), 
there was not room enough upon the summit of Ritigala to allow 
of the development of even one endemic, to say nothing of two or 
three, or of the surprising fact that the most common and wide- 
spread species of Coleus was also living there with the local 
endemic, and in the same or similar places. 


This work fully confirmed the author's doubts concerning the 
efficacy of natural selection, and the weakness of the explanations 
that were put forward in its name. He also became interested in 
endemics for their own sake, for it was becoming evident that 
upon a correct explanation of them depended much of the proper 
understanding of what had gone on in the course of the evolution 
and geographical distribution of plants that had occurred in the 
earth's past history. 

Work upon endemism has been continued ever since the first 
experience upon Ritigala, and has led to many interesting results, 
many of which were published in a book upon Age and Area in 
1922, and others of which it is hoped to publish in another book 
dealing with Geographical Distribution only. One of the first 
interesting points to come out was the very great number that 
were confined each to one (or more rarely to two or more) of the 
mountain summits of Ceylon (57). It was shown that over a 
hundred species were confined to one or more hill-tops. Thus the 
large tropical genus Eugenia showed E. Fergusonii and E. aprica 
in the mountains north-east of Kandy, E. cyclophylla and a 
variety of E. Fergusonii upon Adam's Peak, E. phillyraeoides 
upon Kalupahanakanda, E. pedunculatus in the Rangala moun- 
tains, and E. rotundifolia and E. sclerophylla upon the peaks 
above 6000 ft. The mountains, all rising from a plateau, thus had 
eight peculiar Eugenias, which one could not figure as being 
refugees from the plains by way of the plateau (an explanation 
sometimes advanced). They also contained six endemic Hedyotis, 
ten Strobilanthes, four Atiaphalis, and so on. Plants like this are 
usually supposed to be relics of previous vegetation and it was of 
special interest to notice here what in fact is generally the case 
throughout the warmer parts of the world. The nineteen genera 
that show more than one mountain endemic are represented in 
Ceylon by 268 species, or 14 species per genus against an average 
representation of 2-7 species, and in the world as a whole these 
genera contain 4095 species, or 215 per genus, against an average 
of about 13. They are thus not only very large genera but also 
genera that make up nearly 10 per cent of the whole flora of 
Ceylon, and 2 per cent of that of the world. And this is the 
general rule with regard to endemics, wherever they may occur. 

It looked as if there must be some definite reason for the 
commonness of endemics upon mountain tops, and I suggested 
cosmic rays, though mere isolation might be sufficient. 

The mountains of Ceylon thus behaved, in regard to endemism, 


just like the separate islands of an archipelago, where again the 
endemic species behave in this manner, belonging to large genera, 
with a distinct tendency to differ among themselves upon the 
different islands. It was, therefore, concluded that there was 
nothing peculiar in the existence of an oceanic island that should 
give rise to endemics, other than the qualities that it shares with 
mountain tops, which show like islands in their possession of local 
species. "Of these the most obvious is isolation, and we may, 
I think, justly draw the conclusion that has often been put 
forward, and say that isolation, as isolation, favours the produc- 
tion of new forms" (57). 

The study of endemism begun in Ceylon was recommenced at 
Rio de Janeiro early in 1912, and soon led to the hypothesis of 
age and area about which many papers and a book (66) were 
published in the following ten years. By the courtesy of the 
Editor of the Annals of Botany I am allowed to quote, with 
modification and omission, from a paper of 1921 (65) a short 
summary then written: 

Examining on many occasions, from 1896 onwards, the... 
Flora of Ceylon (46),... I gradually found, somewhat to my 
surprise, that the strictly local species confined to that island, or 
endemic species, as we usually call them, which are very numerous 
in Ceylon, showed on the average the smallest areas of distribu- 
tion there, whether in the grand total or in individual families 
(cf. 70, p. 12). On the older view of the meaning of endemic 
species, which I then held, this seemed a very remarkable thing — 
that species which were generally looked upon as having been 
specially evolved to suit the local conditions should be so rare in 
those very conditions. If these species were specially adapted to 
Ceylon, therefore, it could not be to the general conditions of the 
island, but must be to strictly local conditions within its area. 
There was clearly no difference between island endemics and 
those of the mainland. Accordingly, still more remarkable did it 
seem when I came to study in detail the local distribution of 
these endemic species in Ceylon, and found that, as a rule, they 
were not confined each to one spot or small region characterised 
by some special local peculiarity in conditions, to suit which they 
might have been supposed to have evolved. Not only so, but 
such spots were frequently to be found with no local species upon 
them. Only about a quarter of the whole number were confined 
to single spots, and more than half of those were restricted to the 
tops of single mountains (57). The remaining three-quarters 
occupied areas of larger and larger size,* and in diminishing 
numbers as one went up the scale. . . . The very rare species are 
as a rule well localised, but the rare and rather rare . . . cover areas 


that overlap one another like the rings in a shirt of chain mail. 
Now a little consideration will soon show that from the point of 
view of evolution to suit local conditions this is a verv remarkable 
state of affairs. If A and B grow in overlapping areas, both must 
be growing in the coincident portion, and what keeps A from 
growing into the rest of 5's territory, B into ^'s? In reality the 
case is more complex, for if all the species were entered, there 
would be. . .a dozen overlapping at any one point. It is all but 
inconceivable that local adaptation should be so minute as this, 
with soil essentially the same throughout, and the rainfall, etc. 
varying much from year to year. The species would have to be 
adapted to wide range in rainfall, and to very slight in a com- 
bination of other factors. It was clear that the old ideas of 
particular adaptation were quite untenable. 

Nor would the other popular theory, which equally survives 
to-day, satisf}^ the knowledge that I now had about local distri- 
bution. How could species be dying out in this remarkable chain- 
mail pattern, and why were there so many with small areas? 
Had one perhaps arrived in Ceylon just in time to see the 
dying out of a considerable flora? And why did so many choose 
mountain tops as a last resort? If they had climbed from below, 
they must have plenty of adaptive capacity, and should be able 
to compete with the new-comers. Still more, why did each one or 
two choose a diff"erent mountain?. . .It was difficult to believe 
that the plains were once inhabited by diff^erent species at every 
few miles, whilst many mountains with endemics did not even 
rise direct from the plains, but from a high plateau. 

Counting up all the species of the Ceylon flora, and dividing 
them into three groups — those endemic to Ceylon, those found 
onlv in Cevlon and South India, and those with a wider distribu- 
tion abroad than this (which I termed zvides for short) — I found 
(59) the endemics to be graduated downwards from few of 
large distribution area to many of small (e.g. common 90, rare 
192), and the wides in the other direction (e.g. common 462, 
rare 159), with the Ceylon-South India species intermediate. In 
other words, the average area occupied by an endemic was small, 
that by a Cejdon-South India species larger, and that by a wide 
the largest of all. A cursory examination of other floras showed 
me that their endemic species also behaved in the same way, . . . 
and I Avas at last furnished with what seemed to me to be a much 
more feasible explanation of the distribution of species in general, 
and endemics in particular. 

Having disposed, to my own satisfaction, of the notion that 
endemics were moribund species, I adopted the view that in 
Ceylon the mdes were the first species {o7i the whole'^) to arrive, 
and had therefore on the whole occupied the largest areas. The 
Ceylon-South India species, on my view, must have arisen from 

^ I.e. in any genus the wide would usually be the first to arrive. 


them at points in general south of the middle of the Indian 
peninsula, and would on the whole be younger in Ceylon than the 
wides, and therefore occupy lesser areas on the average. The 
Ceylon endemics would arise from the wides (or Ceylon-South 
Indians) in Ceylon, and would be the youngest, and on the 
average occupy the least areas. All the figures of course must be 
worked in averages, for an endemic of one group might be 
occupying a large area when the first wide of another arrived. 

Confirmatory evidence was soon obtained from the floras of 
New Zealand, Jamaica, Australia, and the Hawaiian Islands. 
The figures for New Zealand are as follows: 

mge in N.Z. 



881-1080 miles 



641- 880 



401- 640 



161- 400 



1- 160 



* Largely undoubted introductions of recent years. 

Facts like these, which are universal, cannot be the result of a 
selection, but must have some more mechanical explanation. The 
only one that to the writer seemed at all satisfactory was simply 
age, as was explained in Age and Area, though of course age in 
itself was not exactly a factor in distribution. There are very 
many factors that may affect dispersal, but if one suppose 
factor a to produce an effect in distribution in a long time x that 
may be represented by 1, one may reasonably expect that in 
time 2x it will produce an effect 2. If the effects of all the factors 
be added up, the total effect in time x may be represented by m, 
and in time 2x by 2m. Obviously there will be great individual 
differences between species, so the proviso was made that com- 
parison (with a view to determining questions relating to age) 
must only be made between allied forms, which were most likely 
to behave in an approximately similar way under similar circum- 
stances. The quickly reproducing, herbaceous Compositae must 
only be compared with other Compositae, not with the slowly 
reproducing trees of the Dipterocarpaceae or the Conifers; and 
so on. One form might even occupy in a decade what might take 
the other several centuries to occupy. And not only must this 
precaution be taken, but closely allied species, even, must be 
taken in tens, to allow of averaging the effects of the many factors 
that might take part in their distribution. But, bearing these 
things in mind, one might say that large area of distribution 


meant considerable age, small area small (each set of plants com- 
pared being taken from the same circle of affinity). 

And also, one must always remember that the distribution of 
plants is very largely controlled and determined by the presence 
or absence of barriers, which may be of many kinds. There may 
be simple physical barriers like the sea, or a mountain chain; 
there may be the barrier of a climatic change from warm to cold, 
or from dry to wet, and so on; there may be ecological barriers 
imposed by the habit or other peculiarities of the plant itself, and 
so on. The whole quesliion is discussed in detail in chap, v (p. 32) 
of Age and Area. 

So axiomatic did all this seem, that the author was somewhat 
surprised by the vehement opposition that it encountered. The 
explanation of this perhaps lies in the fact that geographical 
distribution would thus be transferred to a more mechanical 
sphere than had hitherto been allotted to it. No longer, especially 
in view of the regular arithmetical arrangement, could the natural 
selection theory supply a full explanation of the facts of evolution 
into genera and species, and no longer, in face of the fact of 
increase in number do^\Tiwards in the case of endemics, upwards 
in case of wides (table on p. 29), could it supply a full 
explanation of the facts of distribution, or of the nature of 
endemics. Sooner or later, it seemed to the author, these new 
discoveries meant that natural selection, in its present form at 
any rate, would cease to be so important a factor in evolution, 
and with evolution of course went distribution and many other 
branches of biological science. 

One of the most important things that would necessarily 
follow from the acceptance of age and area was the replacement 
that it asked of the long-cherished notion that endemics in general 
were either relic forms, or local adaptations, by the supposition 
that when they occurred in very small areas they were mostly 
young beginners as species, that had not yet had time to occupy 
larger areas. In many cases of course barriers (especially barriers 
due to climatic or soil conditions) that would in any event obstruct 
or prevent further spread were so close that only small areas 
could be covered, even though the species might be very old. 
Other species, again, of very limited distribution, and that more 
especially in the north within reach of the effects of the cold of 
the last glacial periods, were evidently relics. Sinnott (Age and 
Area, p. 86) gives, as examples of this class in North America, 
Carya, Platiera, Madura, Garrya, Sassafras, Xanthorhiza, 


Baptisia, Nemopanthus, Ceanothus, Dirca, Dionaea, Hudsonia^ 
Rliexia, Ptelea, Decodon, Houstonia, Symphoricarpus, etc., many 
of which are fossil in the Old World. As they also include most 
of the woody endemics of North America, and as each of them 
belongs to a different family, it is highly probable, if not certain, 
that they are relics. But, as already pointed out, they are lost in 
the crowd when considered in connection with their own families, 
especially as most of them are but small genera. And though 
they may be relics of a previously more woody vegetation of 
North America, we have no reason to suppose that they are being 
killed out by superior species — they have probably been much 
reduced by change of climate and are not quite so well suited to 
the conditions that now exist. In warmer countries one com- 
paratively rarely finds endemics of this kind; the endemics, as 
has already been pointed out (Age and Area, pp. 91, 165; and 
p. 26 above), occur chiefly in the large and "successful" genera, 
like Ranunculus or Poa in New Zealand, or Eugenia in Ceylon or 
in Brazil. 

Among these just quoted relics there occurs Ceanothus, with 
forty species in North America only, a genus that must be 
counted as large for that country. In a recent discussion, Arto- 
carpus, the jak and breadfruit genus, which is the third largest 
genus in the large family of the Moraceae, and has over sixty 
species scattered over Indo-Malaya and China, was quoted as a 
relic, on the ground of the occurrence of fossils outside its present 
area. This kind of definition of relic seems to the writer something 
of a begging of the question. We can no longer be sure that any 
plant is not a relic. The whole British flora must evidently consist 
of relics, except perhaps the very local species farthest from the 
land that has been submerged, and yet the flora is in reality a 
very young one in its present position. If a change of conditions 
affect a country, it is in the highest degree improbable, except in 
a case like the coming of the ice, that it will kill out all the former 
flora — it will be gradually and partly replaced by newcomers 
that better suit the newer conditions, and if the conditions change 
back again, these may be in turn replaced by the older flora, and 
gradually things may become much as they were before the first 

One reason, perhaps, for the unpopularity of age and area was 
the realisation that it was incompatible with the current view of 
the way in which evolution had gone on. If we follow it to its 
logical conclusion, it is clear that as the family in general occupies 


a larger area than the genus, the genus than the species, the 
family must be the oldest, or (where, as is often the case, one 
genus covers the family area) as old as its oldest genus. This turns 
the Darwinian theory upside dowTi, for upon it the family is a 
later appearance. There is, however, no evidence for this. How- 
ever far back we go in the geological record, we always find 
families that are identical with some of those of the present day. 
They are also usually widely separated, so that even at that early 
period it is clear that if evolution followed the Darwinian plan, it 
must already have travelled far, though we find no evidence 
whatever of any intermediate stages upon the way. 



J. H E chief result of the work upon Age and Area, perhaps, was 
the discovery of the " hollow curve of distribution " (cf. chap, xviii 
of Age and Area, p. 195), a curve which shows in all cases of dis- 
tribution that I have yet examined, whether of animate or even 
of inanimate things. My opponents have gone to great trouble to 
show that it holds, for example, with the names in a telephone 
book, or even with the distribution by size and shape of a pile of 
gravel, in other words that distribution is in general what one 
may call very largely accidental, and not determined by adapta- 
tion in so far as concerns general distribution about the world, 
which is exactly what I wished to prove. 

The curve was first noticed in 1912 in regard to the flora of 
Ceylon, which consisted of 573/1 (573 genera each with one species 
in Ceylon), 176/2, 85/3, 49/4, 36/5, 20/6 and so on. If one take the 
first few numbers, one finds that the numbers to right and left 
of any single number (e.g. of 176/2) add up to more than twice as 
many (573/1 -f- 85/3 = 658) as itself, so that the curve must be 
hollow as shown in the figures below. It turns the corner between 
3 and 5, and as the numbers get small it becomes more or less 

The curve was also found to show, but not in such detail, with 
the areas covered by species. If one divide the species of a genus 
or family into those of large, small, and medium areas, one finds 
that if one add together the numbers in the large and the small, 
they make more than twice as many as those in the medium, or 
in other words they make a hollow curve, like those shown in the 

Now not only does this hollow curve show with the distribution 
of species by areas, but it also shows with the distribution of 
genera in a family by the number of species that they contain. 
We must always remember that statistics must only be applied 
to numbers and to related forms, which as a general rule will 
behave in much the same way. Take, for example, the family 
Monimiaceae, of 33 genera and 337 species. The two largest 
genera, Siparuna with 107, and Mollinedia with 75 species, range 

WED ^ 



[CH. IV 


(Monimioceoe) PR. 

The familLj consists of SiparunaClO/j, 
Mollinedia(7''), and genera with 
2,2.2,2,1,1,1,1,1, 1,1,1,1, tend 

6. Mexico. 24. Dominica. 

ll.fGuaremala and 25. St. Vincent. 
Nicaragua. 38.Costa Rico. 

19- St. Vincent. 
2 O.Nicaragua 
21. Mexico. 

41. C America 

42. Mexico (frequent) 
51 Costa Rica. 
54Costa Rica. 

Pig. 1. Distribution of Sipariina in South America. The local species in the 
Andes etc. are simply massed together, not shown each in its own place. The 
numbered list shows the localities of northern species. 


from Mexico to Rio de Janeiro or south of it, the smaller genera 
over less districts. Siparuna has one species that covers the whole 
South American area of the genus, some of intermediate areas, 
and a great many of very small areas. Mollinedia, on the other 
hand, though its total area is much the same, has only one species 
that even ranges as far as from Rio de Janeiro to Monte Video; 
most of its species are quite local, and over 95 per cent are so local 
as to count as relics under the natural selection conceptions. Is it 
a failure because of the small areas occupied by the individual 
species, or a success because of their number, and the area 
occupied by the genus as a whole? What is selection doing in 
these two cases? And still more, what is it doing or going to do 
with the rest of the family, where the genera contain 30, 25, 15, 
15, 11, 7, 6, 5, 4, 4, 4, 3, 3, 3, 3, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 
1, 1, 1 species respectively? One cannot draw a line in a curve like 
this, to separate the sheep from the goats. Relics would not be 
made in steadily diminishing numbers, nor would local adapta- 
tion be neatly graduated like this. All families of reasonable size 
show the same curve, as seen in fig. 2, which gives the fifteen 
largest families of flowering plants. Close together though they 
are, the curves never touch. When turned into logarithmic curves, 
as in the next figures (3, 4), they all give approximations to 
straight lines, i.e. they have the same mathematical form, and 
must be the expression of some definite law which is behind 
evolution and distribution, and does not agree with current 
views about these subjects. Many distributional subjects show 
the same form of curve, as may be seen in fig. 5, which shows 
families of plants and animals, lists of endemics, floras, fossils, 
and areas occupied, all mixed up. The curve shows in the names 
in the telephone book, where the very common names are few, 
the very uncommon many. It shows in the list of numbers of 
hotels in towns in the advertisements in Bradshaw, where (in the 
one examined) only London and Bournemouth had large num- 
bers, while a great many had only one each, and there were a 
few in the intermediate numbers. 

This similarity interested me very much, and I have lately 
completed a study of the distribution in Canton Vaud (Switzer- 
land), where I live, of the surnames of farmers, a class who move 
about less than others. Vaud is about the size of Gloucestershire, 
but divided into valleys often separated by very high mountains, 
which make intercourse between the vallevs difficult. After a 
day on the farm, a young man is not going to cross a high moun- 




[CH. IV 

tain range to see his best girl, but marries in his own valley. The 
result has been a very interesting distribution of surnames. 



WITH DirrtRcnT nunBLRi or iPLCiLb. 





Fig. 2. Hollow curves exhibited by the grouping into sizes of the genera in 
the first 15 largest families of flowering plants. Each curve is diagonally 
above the preceding one, as indicated by the heavy black dots (points of 
origin). Note that the curve almost always turns the comer between the 
point marking the number of genera with 3 species, and that marking the 
number with 5 (indicated by the dotted lines). The number after the name 
of the family shows the number of genera in it. 

In a great proportion of the villages in the canton, some 
hundreds in number, there are local names found only (i.e. en- 
demic) in one village each, sometimes on one farm only, some- 
times on two or more. Sometimes the names occur in two or 

CH. IV] 



N2 of species 



■2 -4 -6 -8 10 1-2 1-4 

log (N? Of species) 

Fig. 3. Logarithm curve for Rubiaceae (from WiUis, Dictionary). 
(By courtesy of the Editor of Nature.) 





^ ^ 





■^o 1 


o^ — 

^^v. "" 


— ^ 






■ ' -6 








2 ' 1 

V ' i-e 




Fig. 4. Logarithm curve for Chrysomelid beetles (from old Catalogue). 
(By courtesy of the Editor of Nature.) 



[CH. IV 

more villages, but always in diminishing numbers as one goes 
upwards, just as with the plants. Most often the villages are in 
the same neighbourhood, but at times they are as far off as a 

Monospecific Genera at this end of curve 

• C 

ft) ^ 
. «■ "^ j- 

/June of Genera 

Number of species (or size of area.J 

Fig. 5. Mixed curves, to show the close agreement of the hollow curves, 
whether derived from families of plants grouped by sizes of genera (Com- 
positae, Hymenomycetineae, Simarubaceae), families of animals (Chryso- 
melidae, Amphipodous Crustacea, Lizards), endemic genera grouped by sizes 
(Islands, Brazil, New Caledonia), local floras grouped by (local) sizes of genera 
(Ceylon, Cambridgeshire, Italy), local faunas (Birds of British India, British 
Echinoderms), Tertiary fossils by sizes of genera, or Endemic Compositae 
of the Galapagos by area. [By courtesy of the Editor of Nature.] 

man can walk in one or two days, their distances and the tracks 
on which they lie showing the directions of emigration of young 
fellows in search of work. 

The distribution of species of plants that occurred in Ceylon, 


for example, outside the island, was found to go, on the average, 
with their distribution inside the island,^ but natural selection 
could not adapt a plant that was to come, say from West Africa, 
to suit Ceylon better than a plant that had only come, say from 
Bombay. If anything, one would expect the latter to suit Ceylon 
the better. And the same thing showed with the names of the 
farmers. Rochat is a very common name in the valley of Joux, 
and has spread farthest into the country round, while the names 
that are less common have spread less. It is impossible to main- 
tain that the possession of the name Rochat gives any advantage 
in the struggle for existence as against the name Capt, which is 
less common in Joux, and has not spread so far beyond it (fig. 6). 
Natural selection can have nothing to do with the distribution of 
surnames, which behave just like species of plants. 

All these various curves match, and must be determined by 
the same rules. There would seem to be a necessity to reconsider 
the idea that distribution is determined by natural selection, as 
indeed we have already seen. Adaptation can only be to the con- 
ditions that exist round about the plant, and it is absurd to 
suppose that the bulrush or the silverweed, for example, that 
(in the same specific form) occurs in New Zealand as well as in 
Europe could have become, in Europe let us say, adapted to 
New Zealand conditions. That it suits them is simply due to luck, 
and to local adaptation, as it slowly moved from place to place. 
But in any place where it was not fairly well suited, it would 
usually be killed out remorselessly and promptly by natural 

Many other cases might be brought up, but the fact that distri- 
bution shows these hollow curves, which cannot be explained by 
aid of the theory of natural selection, will suffice to show that 
that theory in its turn is meeting with almost insuperable diffi- 
culties. It was difficulties like this which made my friend 
Dr Guppy, who had devoted most of his life to the study of 
distribution, adopt in 1906 the theory of evolution by diff'eren- 
tiation, whilst, as the result of completely independent investiga- 
tions upon different lines, I myself adopted it in 1907. The theory 
itself is pre-Darwinian. The idea that underlies it, as formulated 
by Guppy, is that in the early days of the flowering plants the 
climates of the world were damper and more uniform. The world 
as a whole seems to have become drier since that time, so that the 

^ I.e. a plant widely distributed in Ceylon was on the average widely 
distributed outside it. 



[CH. IV 

climates must have become more differentiated into damper and 
drier, warmer and colder, etc., than they once were. With them 
the plants have become differentiated, and it was commonly 
supposed that this was done, as in the theory of natural selection, 


Distabution of name THEVENAZ 

•agriculturist ♦commercial or professional -5" Crotx»V' ^'*' 

^ C6.S0O mK ) ♦ ^f 




j!/ (<2,000lnh 


(J.SOO inh) 


DlstrLbutlon of name ROC HAT 

& po9sibl< varittUi ROJARD, R055AT. RUCHAT 
• agriculturist. ♦ commercial or professiooa 

o I 1 a fc S t T » < l a 



Fig. 6. Distribution of two surnames, Thevenaz and Rochat, 

in French Switzerland. 

more or less in suitability to the various climates, but that the 
whole specific or other difference appeared, not by gradual 
adaptation, but at one step. The writer, however, is not prepared 
to admit that these things are necessarily connected, without 
further evidence. 


To this, I have added the facts of the hollow curves, which are 
universal, not only in the distribution of plants and animals, but 
in other things, as we have just seen in the case of that of the 
farmers' surnames in Vaud, which matches to a nicety the distri- 
bution of plants. It seems to me impossible to reconcile these 
curves with the theory of natural selection, and there are other 
very serious objections to this latter theory. To reconcile the 
theory of differentiation with the hollow curves, I have added to 
it the supposition that the evolution that goes on, and which is 
shown in the morphological characters of plants, has little or 
nothing to do, directly, with adaptation, and certainly not with 
direct adaptation. The characters do not necessarily indicate 
adaptation at all. Every now and then a character appears, like, 
for example, climbing habit, of which natural selection can make 
use, and which is therefore retained, but natural selection was 
not the direct cause of its (complete) appearance, nor was its 
appearance, in all probability, as accidental as that theory would 
involve. It appeared full-fledged, and was advantageous, or at 
any rate not harmful. And if it had no necessary adaptational 
value behind it, there was no particular reason why a species 
showing it should spread at a different speed from other species 
of the same or closely allied genera, a supposition which at once 
made the hollow curves a normal feature of distribution. And 
there was also no reason why the many new species that have 
appeared should not appear at a rate that was in any case not 
determined by the necessities of adaptation, as we have seen in 
the case of the Podostemaceae. A species that reached a sand 
dune, for example, if it were reasonably suited to it upon arrival, 
would gradually adapt itself in more detail to some definite local 
conditions there, by physiological adaptation controlled by 
natural selection. 

What the mechanism was by which this evolution was carried 
on, we do not know. I suggested in 1907 that "a group of allied 
species represents so many more or less stable positions of equi- 
librium in cell division". 

The occurrence of the hollow curve for distribution of plants 
by areas, or for distribution of genera by numbers of species, 
shows that neither in geographical distribution (strictly so-called) 
nor in evolution can natural selection be invoked as it once was, 
as the principal factor. Any influence that it has must either be 
very small, or else exerted in an indirect way. One cannot, upon 
such a curve, draw any dividing line, and say that those upon 

42 THE HOLLOW CURVE [ch. iv 

one side are to be regarded as successes, those upon the other as 
failures. Nor can one picture to oneself a system in which the 
number of failures that die out (and in all families more or less 
alike) is at first to be about 38 per cent (the monotypic genera, of 
one species), then only about 12 per cent (the genera of two 
species) and so on in decreasing numbers. 




X HE coming of mutation was mentioned above (p. 14) and it 
was pointed out that it seemed to get over some, at any rate, of 
the difficulties inherent in the employment of gradual variation. 
In particular, as the new form was qualitatively, and not merely 
quantitatively different from the old, the change was differen- 
tiating. Further, it was practically irreversible, and might also 
be hereditary. 

But it was gradually realised that its employment brought in 
its train other difficulties which were almost as great, so long, at 
any rate, as one adhered to natural selection as the driving force 
in evolution. This adhesion definitely handicapped the theory, 
preventing it from giving its proper stimulus to biological progress. 
Since people wished to combine it with natural selection, they 
had to stipulate that mutations must be very small. It was very 
hard to see how it could work with large mutations that might 
effect such differences as distinguish the Monocotyledons from 
the Dicotyledons, or even those that divide one family or genus 
from another, and which might change the whole character of the 
plant. If these were to be allowed, one could no longer imagine 
progress by small, gradual, and progressive adaptation, and this, 
determined in everj^ detail by natural selection, was still the 
ruling principle invoked in evolution. If we remove direct 
advantage from the list of factors that mav be immediatelv 
operative in causing evolution to go on, it is evident that the 
structural mutations that distinguish one form from another 
need not, perhaps even cannot, proceed in gradual stages, unless 
there be, as of course is by no means impossible, some at present 
inscrutable law that guides them. But fossil evidence gives but 
little support to this conception. Real intermediates are rare; 
what are commonly called intermediates are usually things that 
combine some of the characters of one with some of the other. If 
one find a plant showing, to give an imaginary case, four of the 
characters of Ranunculaceae to three of the Berberidaceae, it is 
sure to give rise to discussion and dispute. 


More than thirty years ago the writer published a paper upon 
the distribution of the Dilleniaceae (72), in which he adopted the 
notion that mutation might at times be so large that there might 
appear in one step a new species, or perhaps even a new genus. 
Intermediate stages were not considered to be necessary, though 
it was pointed out that in one or two cases intermediate forms, 
perhaps hybrids, were found living side by side. 

By that time the author had completely discarded the theory 
of natural selection as the chief driving force in evolution, re- 
garding it primarily as a means of getting rid, promptly, of 
anything that was seriously unsuited to the conditions under 
which it had to live. There was, of course, no definite reason why 
selection should not at times, under favourable circumstances, 
produce new forms, but it seemed unlikely that such production 
was at all common, or that it should produce forms of specific 
rank. It could not be looked upon as operative in regard to the 
bulk of the morphological characters which show us that evolution 
has gone on, and which in consequence have always tended to be 
regarded as in some way showing progressive adaptation. The 
author had also abandoned the idea that there was such wonderful 
morphological or structural adaptation in the flowering plants. 
Each, of course, must be fairly well suited to the place in which it 
grew, for if it were not, natural selection would soon dispose of it ; 
but that was all, in most cases. Real adaptation was largely 
internal as was clearly indicated (1) by the enormous range of 
many species without any serious morphological change from one 
region, or one set of conditions, to another; (2) by the great 
numbers of plants that were to be found in the same conditions 
(as nearly as made but little difference) and yet showed such great 
morphological differences that they could be classified into many 
different families and genera, though they might all come into 
one ecological category, like the Podostemaceae or the plants of 
a moor or a sand dune. The common plants of a moor in Britain, 
for example, include Betula, Calluna, Carex, Cornus, Empetrum, 
Erica, Kobresia, Listera, Molinia, Nardus, Potentilla, Scirpus, 
and Vaccinium, covering a great range of the flowering plants, as 
can be seen at a glance. Another indication (3) was the great 
numbers of species of one genus that might at times be found in 
similar conditions, like Mesemhryanthemums in South Africa, 
while single species of other genera ranged over great differences 
in conditions. 

The structural differences that showed in plants to such an 


extent were often so clear cut, and so distinct, that it seemed to 
the writer quite evident that they must in general have been 
formed by sudden change, or mutation. Gradual change, picking 
out advantageous variation, would be very unlikely indeed 
always to produce tlie same structural character, such, for example, 
as is sho^vn by a berry or a drupe, or by opposite leaves. Why 
should berries be most often found in the near (systematic) 
neighbourhood of capsules, drupes in that of achenes or nuts? 
Why should selection pick out leaves that were exactly opposite, 
ovules with the raphe exactly dorsal or ventral, or why such 
clearly marked and exactly formed fruits as capsules, berries, etc. ? 
Selection would obviously act with decreasing force as the leaves 
came nearer and nearer to being opposite (or alternate, for then 
they show a definite phyllotaxy or arrangement), or the raphe 
to being dorsal or ventral, etc. In actual fact, between many of 
these characters, intermediate stages were not possible. One 
could only take the one or the other side of a very divergent 
variation, such as alternate or opposite leaves, dorsal or ventral 
raphe, etc. The mutation, in so far as the characters themselves 
were concerned, paid no attention to functional or adaptational 
requirements. It was impossible to conceive of any adaptational 
need that would ensure that all Monocotyledons should have a 
single cotyledon, together with a parallel-veined leaf, a trimerous 
flower, and a peculiar anatomy. There is not even a "mono- 
cotyledonous " mode of life to which this great morphological 
change might be supposed to adapt them. For that matter, 
there is not even a " ranunculaceous " or a " thalictroid " mode of 
life. The larger a genus, family, or other group of plants is, the 
greater is the variety in the conditions of life in which it is found 
(comparing, as usual, only related forms), and also the larger the 
area covered by single individual species of the family or genus. 
To return to the Dilleniaceae; assuming that mutations could 
be of generic size, the author drew up a scheme according to 
which the whole tree of the family could be looked upon as 
derived by descent from a genus so comparatively simple in 
structure, and so widely distributed, as Tetracera. A sketch was 
drawn of a suggested manner in which the evolution might have 
proceeded, showing all the existing genera, which might even be 
the whole tree of the family. Of course some geological or other 
catastrophe might have killed out some more or less local genera, 
though it would be unlikely to have done so to any genus that 
was already very widespread. Incidentally Tetracera is not the 


largest genus in the family, but it is the most widespread, and 
when these two characters do not agree in pointing out what is 
probably the oldest genus, the author considers that distribution 
rather than size should be regarded as more important. 

In thus supposing that a genus could appear at one stroke, and 
that one genus could, directly, give rise to another, the author 
was definitely going beyond mutation pure and simple, and 
adopting the theory of differentiation, in which, as the changes 
were large, the idea that the morphological differences represented 
adaptational improvements was discarded. In other words, 
though evolution was unquestionably going on, and was on the 
whole, though more notably in the animal world, producing 
higher and higher types, there was no need to suppose that there 
was necessarily any adaptational reason in the innumerable 
structural changes that showed themselves in the course of that 
evolution, and indeed showed that evolution was going on at all. 
It seemed much more probable that most of those features which 
we were accustomed to call adaptational improvements had 
appeared already full-fledged. If new features that thus appeared 
were really harmful, or met with ill-luck, they were promptly 
removed by the action of natural selection. If they were bene- 
ficial, or not harmful, and met with average luck, they were 

The sketch showed the way in which it was suggested that 
evolution had proceeded, from the large and widespread genera 
down to the small and local, but there was then about as much 
chance to prove this kind of mutation as to prove that natural 
selection could do what was required to form a new species, for 
it must not be forgotten that this has not yet been done. There is 
some reason to suppose that it can produce new varieties, but 
no proof that it can cross the line of mutual sterility that usually 
lies between species. Both theories derive varieties from a parent 
species, but selection derives them from a parent which is at an 
earlier stage of development, and perhaps fated to die out, the 
varieties being considered as on the way to species. Differentia- 
tion does not admit this, but regards them as later stages of 
development by mutation than the species that gave rise to 
them, and with which they are not necessarily in competition, 
though perhaps they may sometimes go on, by further mutation, 
to become new species. The essential point at present, for dif- 
ferentiation, is to prove that evolution proceeded in the direction 
from family to species, and not the reverse. 


When one looks at the great differences that exist, for example, 
between the Dicotyledons and the Monocotyledons, and these in 
several different points, it seems to be an unnecessary handicap 
to accept the idea that mutations must necessarily be small, 
especially when we have no facts to prove that this must be the 
case. The characters are so completely unrelated to anything in 
the way of adaptation that it becomes very difficult to conceive 
of them as having been gradually acquired, especially when one 
remembers that intermediates between them are all but im- 
possible, and could not in any case have any adaptational value, 
so that unless there is some recondite law in the background 
that can force things to proceed in such a manner, there seems no 
reason for it. There might for example, be (probably is) some 
physical or chemical law that at present we do not know, com- 
pelling genes or chromosomes to behave in a certain way.^ But 
as one sees the phenomena at present, how can one pass by 
gradual stages from two cotyledons to one (or vice versa), from 
net veining to parallel, from a 5-merous to a 3-merous flower, 
from the one kind of anatomy to the other? The only reasonable 
way to account for it is to suppose that the characters of Mono- 
and Dicotyledons were handed down as the lines of descent 
resulting from a mutation in very early times which split off the 
one from the other. No adaptational difference can be found, nor 
is there any " monocotyledonous " mode of life. As one comes up 
the scale from species, the plants are found to grow in greater and 
greater variety of conditions, and to belong to more and more of 
the various ecological groups. If monocotism suit a grass or a 
bamboo better than dicotism, why does it also suit a tulip, a 
Zostera, a Potamogeton, an iris, or an orchid? And why, if there is 
any adaptational difference betw^een the two great groups, do 
they occur with such regularity in almost every part of the world 
in the proportion of one to four? There are small places where 
these figures vary very much, but the only large ones are usually 
near the limits of vegetation, a fact which suggests that there are 
differences in age between the two groups. Hooker pointed out 
this numerical relationship in 1888 (18), and it remains one of the 
many problems in geographical distribution which are com- 
pletely inexplicable upon the hypothesis of natural selection, and 
which are left unmentioned by its supporters. 

Another direction in which the theory of mutation makes 

^ My friend Dr C. Balfour Stewart suggests that it is probably electrical, 
as is probably the spUtting of the chromosomes in reproduction. 


things much easier to understand is the widespread correlation 
of characters, for which natural selection can offer no explanation. 
Why is the possession of tendrils, or of hooked leaves or stems, 
always accompanied by a weak and flexible stem? Why has a 
dorsiventral leaf, such as is possessed by a vast number of plants, 
always a layer of palisade tissue towards the upper side, for 
making the best use of the light that falls upon it? Why, in the 
Compositae, have the heads of flowers an involucre of bracts, 
why has the style two stigmas, why is the ovary unilocular, why 
is there only one ovule and that erect, and why is there no endo- 
sperm? And why do all these characters go together in practically 
every instance in a family of 18,000 species? The same sort of 
questions may be asked for any other family, whilst they would 
be absurd in the case of adaptational characters. Nothing but 
descent from a common ancestor (or ancestors) will explain 
them, and evolution upwards from individuals and varieties will 
not do it; it must have been the other way, as differentiation 
would have it. Evolution apparently must go on, at any rate if 
the appropriate stimuli are present, but there is no necessary 
adaptational reason for much of it, at any rate, and we find 
practically no gradual stages in the fossil record. To accept 
mutation, and that of any necessary size, would seem to be the 
simplest theory upon which to work until something better 
turn up. 

An objection often brought up is that no such mutations — 
large, viable, not recessive, and not lethal — have been seen. But 
no one has ever seen a species formed by natural selection. Yule 
has estimated that one such mutation in fifteen to thirty years, 
upon any small spot of the earth's surface, would be sufficient to 
account for all the flowering plants that exist. The chance of 
seeing such a mutation is all but non-existent, and if the result 
were found at present, people would at once put it down as 
another relic and leave it at that. Until we can control mutation 
— and signs are not wanting that we may be able to do so at some 
future time — we can hardly hope to get proof for this proposition. 

One must not forget that the mutations that have been studied 
have, as a rule, been mutations that have occurred in cultivated 
plants, or otherwise in unnatural conditions, conditions which in 
themselves perhaps stimulated a greater mutability than usual. 
We have not properly considered the case of mutations under 
completely natural conditions, which are well kno^vn to be much 
less common. If a mutation appear in a seedling of some tree in 


the jungle, the chances are that it will inherit the suitability of 
its parents to the local conditions, and that if the mutation be not 
seriously harmful, it will not be interfered with in any way by 
natural selection, and will be allowed to survive, and in time, if 
hereditary, to propagate itself. May it not be that something of 
this kind is an explanation of the great majority of the innu- 
merable structural differences that we see in plants, and which 
so often only appear when the serious struggle for existence is 
over, or practically over? One cannot imagine that it can have 
any importance in the struggle for existence whether a plant 
have or have not one or two cotyledons, a parallel- veined or a 
net-veined leaf, a 3-merous or a 5-merous flower, and so on. To 
the vast majority of the characters upon which we base our 
classifications natural selection is probably completely indif- 
ferent. It is well known, incidentally, that most of those 
characters which we consider as usually of family rank (App. I) 
may at times appear as generic, or even specific, so that it is 
evidently quite easy for them to be acquired, while at the same 
time the structural agreement between them is amazing. Nothing 
but sudden mutation will easily account for such phenomena. 

A case in which mutation of this kind looks as it might have 
happened in nature is that of the columbine {Aquilegia), which 
looks as if it might have arisen from the larkspur {Delphinium), 
the latter having a dorsiventral flower with one spur, the former 
a regular flower with five spurs. Nothing but mutation can cross 
the (numerical) gap between these genera, and one actually sees 
an almost exactly similar mutation happening frequently in the 

A good illustration (and dozens similar to this could be given) 
of the very great probability of large mutation is that afforded 
by the three families Centrolepidaceae, Eriocaulaceae, and 
Restionaceae, all of which, independently, split into two sections, 
Diplantherae with dithecous anthers, and Haplantherae with 
monothecous. One cannot conceive of this by anything but a 
direct mutation, which would produce morphological similarity 
in all. 

Some quotations bearing upon this subject may be made from 
a paper now of some age (57), in which attempts were made to 
show that local or endemic species were usually separated from 
the widely distributed, and usually fairly closely related, species 
that accompanied them by differences which could only be 
passed over by mutations, often "large". 



Ranunculus sagittifolius, confined to the high mountain region 
about Nuwara Eliya (Ceylon), differs widely from the only other 
Ceylon buttercup, R. Wallichianus (South Indian also), which 
occurs side by side with it, though in drier and sunnier places, 
but is closely allied to R. reniformis of the mountains of the 
western Indian peninsula, differing mainly in the petals, which 
are five in the Ceylon species, twelve to fifteen in the Indian one. 
. . .Are we to suppose the conditions of life so different in the 
Ceylon and Indian mountains that a five-petalled flower will suit 
the one, a twelve-petalled the other? Or how is the one to pass 
into the other, or both to arise from a common ancestor, except 
by discontinuous variation? Can it be supposed that the simple 
obovate-lanceolate leaf of Acrotrema intermedium fits it for the 
Kitulgala district (Ceylon), while the pinnate leaf with linear- 
lanceolate segments of A. Thwaitesii fits that species for the 
Dolosbage district, but a few miles away, a trifle higher up, and 
in a similar climate?. . .A. lyratum, characterised by very long 
peduncles, is found only on the summit of Nillowekanda, an 
isolated precipitous rock. . .is it to be supposed that the long 
peduncles are any advantage . . . ? W^hat advantage can the two 
ovules of Polyalthia Moonii and P. persicifolia be against the one 
of the other species? P. rufescens, another species with two ovules, 
and closely allied to both, occupies the Cochin district of South 
India, and why should there be three species in so similar a 
country . . . ? And how did the one form arise from the other, or 
both arise from a common ancestor, except by mutation? Similar 
queries might be asked 800 times for the 800 endemics ... in the 
Ceylon flora. 

The only possible explanation to my mind was that provided 
by the "parent and child" theory, that parent and child might, 
and very often did, exist side by side. 

The general principle on which India and Ceylon have been 
peopled with the many species which they contain would seem to 
be that one very common species has spread widely, and, so to 
speak, shed local endemic species at different points, or in other 
cases that one species has spread, changing at almost every point 
into a local endemic species, which has again changed on reaching 
new localities. 

A very good proof for mutation, and indeed for differentiation 
also, is provided by the work done by Mr G. Udny Yule and the 
writer upon the statistics of evolution (76). We showed that the 
evolution of new genera out of old followed with very great close- 
ness the rule of compound interest. After some time one genus 
becomes two, and so on. But if genera are formed like this it is 
hard to believe that they can have been formed by gradual steps, 


and it would also show that the larger must be in general the 
ancestors of the smaller. Evolution seems to have proceeded 
upon a definite plan; "the manner in which it has unfolded itself 
has been relatively little affected by the various vital and other 
factors, these only causing deviations this way and that from the 
dominant plan". 





jT^daptation, or suitableness, with an implied meaning of 
having been suited by some particular agency, is a subject that 
has been as much discussed as any in biology, and especially 
since the publication of the theory of natural selection, which is 
essentially based upon it. Under that theory a new organism 
only comes into existence because it is an adaptational improve- 
ment upon that from which it is derived. In other words, im- 
provement in adaptation is the only reason for which new organisms 
are evolved. But the only thing that shows that they are new 
organisms is a structural or morphological difference between 
them and other forms, even if the latter be obviously closely 
related to them. It was, therefore, taken for granted (it could 
hardly be otherwise) that the 7norphological or structural characters 
were the expression of the adaptation that had gone on, and therefore 
had, themselves, a greater or less adaptational value. 

Once this was fully realised, there was a great rush into the 
study of adaptation, especially during the 'eighties and early 
'nineties of last century. But in spite of all the work that was 
put into it, no one ever succeeded in showing that even a small 
percentage of the structural characters, that were the reason why 
plants were divided into so many families, genera and species, 
had any adaptational meaning or value whatever. No value 
could be attributed to opposite as against alternate leaves (or vice 
versa), to dorsal against ventral raphe, to opening of anthers by 
pores or by slits, and so on. 

In the characters of the plants of average moist climates (often 
called mesophytes, as occupying the middle position), it was very 
difficult to find anything that could be called in any way adap- 
tive, except those general characters which are common to most 
of the higher plants and occur in almost every kind of conditions, 
such as roots (which are adapted to taking up food), leaves 
(adapted to forming food by aid of the energy of light taken in), 
flowers, fruits, seeds, etc. But as one went outwards to either 
extreme, to the water plants (hydrophytes) on the one side, or to 


the plants growing in dry climates (xerophytes) on the other, one 
began to find characters more or less individual to the species, 
that had something definite to do with the mode of life of the 
plants, and which therefore might be called adaptive characters. 
On the one side one found the somewhat negative characters of 
absence of strengthening tissue and absence of stomata, with 
diminution or absence of the roots ; on the other side one found 
the more positive characters such as sinking of the stomata in 
pits, hairy or waxy leaves, and in the most extreme cases, such as 
the cacti, of storage of water in the tissues. But few of all these 
characters, of whichever group, though they might make great 
changes in the general look of the plants, were of great importance 
in the separation of plants into species, or into genera, and still 
less into families. There is little evidence that even such great 
adaptations as are involved in the development of hj^drophytes 
or of xerophytes can cause such great morphological or structural 
differences as actually exist between plants. A mere glance at the 
composition of any ecological group of plants that are suited to 
any given situation is sufficient to show the truth of this. Take, 
for example, the plants that occur in boggy places in Britain, 
of which lists may be found in Tansley (44) or Bonnier. There 
are about twenty genera represented, of which eight are Mono- 
cotyledons, whereas the average proportion of Monocotyledons 
is only one in five. Among woodland plants they are one in three, 
whereas upon cliffs they are absent. Though the differences 
between them and the Dicotyledons are about the most important 
structural differences that occur, there is no evidence to show that 
they have any adaptational value whatever. The bog plants also 
show both alternate and opposite leaves, superior and inferior 
ovaries, capsules that are septicidal and loculicidal, and that 
open by lids, that are divided into several loculi or have only 
one, whilst there are also achenes, follicles, berries, drupes, and 
schizocarps among the fruits. The twelve genera of Dicotyledons 
belong to ten different families, including both Polypetalae and 
Sympetalae, and so on. In Ericaceae, where two genera occur, 
one has a berry, the other a capsule. Nowhere is there any indi- 
cation that the supposed structural adaptation had anything to 
do with the fact that they all live in bogs, and must therefore be 
adapted, or suited at any rate, to that mode of life. Other 
British ecological groups of plants — those of chalk-downs, moun- 
tains, and dunes, etc. — will show similar results. Everywhere one 
finds that there are plants showing the important characters of 


classification and distinction, and even showing, in many cases, 
both members of the contrasting pairs that are given in the list of 
family characters (Appendix I). These characters show no relation 
whatever to any of the ecological features that may give the 
character to the locality. Almost any family or genus, if large 
(i.e. old, upon the theory of Age and Area, with its subsidiary 
Size and Space) may be found in almost any kind of locality, 
represented by some of its species. For example, in the bog flora 
just mentioned, there occurs Sedum villosum, a member of a large 
genus of 450 species usualh^ xerophytic. And not only so, but it 
is a hairy species, bearing a character usually specially associated 
with xerophytism. Morphologists have long maintained that 
structural characters have nothing to do, directly, with the life 
or functions of the plant, and it would appear that they are right 
in this contention, which violently contradicts the supposition of 
selection as a chief cause in evolution. The evolution that has 
produced more than 12,000 genera and 180,000 species has not 
been, primarily, an adaptational evolution, as the writer tried to 
show twenty-five years ago in the case of the Podostemaceae. 

The agency by which plants were to become adapted to the 
conditions in which they were found was, of course, that of 
natural selection, for the competition upon which it is based, 
which we call the struggle for existence, will evidently kill out 
those that are in any way seriously unsuited to the conditions. 
It may also kill out some or many of those that are well suited, if 
they be in any way handicapped, as by too shady a position when 
in the seedling stage, by a poor water supply, or by many other 
things. But in itself this killing out would not produce any 
advance in complexity of structure or function, the things that 
we regard as showing that evolution has gone on. Certain assump- 
tions were therefore needed. Only advantageous changes could 
be picked out, and it was therefore supposed that (usually) when 
a gradual change of local conditions began, some of the offspring 
varied in such a direction as to give them an advantage. It had 
also to be assumed that the parent did not vary in this way. The 
process being repeated in every generation (another assumption), 
the improved forms always winning, the difference from the 
parent ultimately became specific, showing as a rule more or less 
sterility when crossed with the parent. The parent was supposed 
not to adapt itself (yet another assumption), but to become a 
relic and gradually to die out for want of offspring viable in the 
new conditions. 


For such a process to be successful, there are other assump- 
tions that we must make. We have (1) to assume — which goes 
against much or most of the evidence — that a morphological 
change has some adaptational value, (2) that such a variation 
will appear at the time when it is wanted (for otherwise there will 
be nothing for natural selection to work upon), (3) that the 
conditions will continue to vary in the same direction long enough 
to permit of the adding up of small variations until the specific 
(sterility) line is passed, (4) that the operation is so strenuous 
that at some point upon the way the sterility line will be safely 
passed, (5) that at some point when the species is fully embarked 
upon the change, a better variation, but working in another 
direction, is not offered to it by nature, thus confusing the result, 
(6) that when one variation has achieved its full result, it shall be 
followed by another, often in a completely different direction 
(for one species usually differs from another in several characters) 
without interfering with the mutual sterility, and (7) that the 
variation is so eminently desirable that it will be followed up 
until the new structural feature, for instance alternate (or oppo- 
site) leaves, palmate, pinnate, peltate, stipulate or exstipulate, 
gland dotted, or other type of leaf, anther opening by slits, valves, 
or pores, dorsal or ventral raphe, achene, follicle, pod, nut, 
schizocarp, berry, drupe, etc., is fully perfected. 

The whole thing is largely based upon the third assumption 
given above. For example, the climate (not the weather) must 
change gradually in the direction of warmer or cooler, wetter or 
drier. But these changes are well known to be so slow that they 
can only be detected in averages of a century or more — a period 
longer than the life of most plants, except many trees — whilst 
weather is continually changeable. Suppose a plant to have 
begun to vary in the direction of suitability to increased drought, 
and then there comes, as so commonly happens, a cycle of wetter 
years; what is going to happen then? Botanists have somewhat 
neglected weather effects, when compared with agriculturists. In 
the RepoH of the Sudan Agricultural Research Service for 1937, 
which I have lately reviewed, it is stated that the average good 
yields of the whole Gezira, in which the weather conditions were 
as stated, were reflected on the Government Farm, where the 
yields were much the same; "and once again we get an illustra- 
tion of the comparatively small effects which local conditions 
may have". This is familiar to all who have to do with crops, and 
puts considerable difficulty in the way of anyone who imagines 


local adaptation to local needs, except upon very large areas. 
Would adaptation be likely steadily to follow a line based only 
upon averages, in such circumstances ? It would hardly seem likely. 

U 4 cotton, one of the great successes of cotton breeding, was 
locally bred at Barberton in the Transvaal for certain needs, and 
has proved to be a superior cotton for an immense area. But a 
Darwinian species would almost certainly be a species produced 
upon a local area, and if it began to spread about in its early 
stages it would be lost (as Fleeming Jenkin showed) by crossing 
with its neighbours, a fate from which U4 was, of course, carefully 

Conditions other than those of climate or soil are hardly likely 
to change continuously in one direction, except upon broad 
general lines, such as a change from forest to grassland or vice 
versa, and even this is probably determined by climatic change. 

There is another type of adaptation, which we may call 
adaptation to movable conditions. A climbing plant will remain 
adapted to climbing almost anywhere that there are erect plants, 
so long as it is suited to the climate and other general conditions. 
A water plant can travel over an immense area, finding suitable 
conditions in innumerable places. The American pitcher plant, 
Sarracenia, is now quite happily established in a bog near to 
Montreux, and so on. 

Geographical distribution was also explained by the selec- 
tionists as based upon adaptation. The better adapted species 
were those that spread the furthest. But how did a species 
become adapted, let us say in Asia Minor, to the conditions that 
occur in New Zealand? It must be just a case of luck. If the 
species were old, so that it had plenty of time to adapt itself 
wherever necessary, and as in this case it would probably have a 
good deal of capacity to withstand extremes, or adaptability, it 
would probably be able to find places whose existence would 
enable it to get across the vast distances. When at last it reached 
New Zealand it would probably soon find places in which the 
conditions were sufficiently like those just left to enable it to live 
there. One would, perhaps, expect those plants that were 
evolved in regions where there was great variety of conditions to 
be those most likely to spread widely ; it may be so, but we have 
at present no evidence to go upon. 

In dealing with the adaptation of a plant to changed conditions 
man always tends to be in too great a hurry. When Europeans 
first went to the tropics, they tried to acclimatise there the plants 


of Europe, with no success except in the high mountains, where 
many herbaceous, but rarely arboreous, things have taken a hold 
upon ground from which the original plant associations had been 
removed. In the same way they tried to acclimatise in Europe 
tropical things like the dahlia or the potato, but even after the 
lapse of centuries these plants remain "half-hardy". In both 
these cases the change of conditions was too great to allow of 
physiological adaptation, which might perhaps have taken place 
in a gradual acclimatisation over a very long period of time with 
only very slight alteration in conditions at each step. Or it may 
have been only that the range of capacity to withstand conditions 
was not sufficient even after the utmost had been done in accli- 
matisation. Time and gradual progression are the most essential 
things in acclimatisation. 

A very great difficulty in the path of acceptance of natural 
selection as a cause for gradual adaptation is the fact that so 
many of what look like real morphological adaptations require so 
much correlation. Climbing plants come into this group, though 
they are obviously well suited to climbing. The habit cannot be 
difficult to acquire, for there are so many cases of the closest 
relatives, one climbing, one erect. A climber also needs a support, 
which is usually an erect plant, so that erect plants must have 
been the earlier. But one cannot imagine natural selection 
picking out the beginnings of weak and flexible stems, whether 
by gradual change or by small mutations. And when at last they 
were formed, as obviously there would be no value in developing 
tendrils or other means of climbing until the stems were weak, 
they would collapse into the darker lower levels of vegetation, 
and would have to undergo physiological adaptation to living in 
greater darkness. Then they would have to learn to form climbing 
organs, and finally, learning to climb, they would once more have 
to adapt themselves to life in greater light. And what use would 
the beginnings of tendrils or other climbing organs be? And why, 
after having learnt to live in greater darkness, should the plant 
want to grow up into the light once more? Yet it would be dragged 
up by the tendrils, and would probably suff'er from the excess of 
light. There is too much, and too complicated internal adaptation 
required, to say nothing of the external. One must look with 
great suspicion upon such an easy interpretation of such struc- 
tural features as climbing stems as being simply adaptations. If 
they were gradually formed, the work was too complicated for 
natural selection to perform. 


It is clear that in adaptation to climbing a large part of the 
adaptation, if not perhaps all, must be internal and physiological, 
and we are inclined to think that it is to such adaptation that 
the name should be practically confined, while such things as 
climbing plants might be called suited to climbing. If a plant, as 
will usually be the case, move only a very small distance from the 
parent, it is probable that it will not need more than the minimum 
of physiological adaptation to suit it to the new place, and so on 
at every move. But such adaptation will not necessarily show 
any morphological changes visible to the outside. If one look at 
the distribution of such a widespread plant as Hydrocotyle 
asiatica, which ranges from the plains of Ceylon, with a tem- 
perature range of 70-90° F., to the south of New Zealand with 
winter snow and frost and a weak sun, one finds it to be essentially 
the same plant throughout. The Ceylon plants are suited to the 
Ceylon conditions, the New Zealand to those of New Zealand. 
But it is customary to speak of it as "adapted" to both. If it 
suits them both, it must be just a case of luck, with local adapta- 
tion going on as it has moved from one to another. One very 
much doubts, after considerable experience with acclimatisation, 
if seed from the plains of Ceylon would suit New Zealand without 
a lot of previous physiological adaptation, or vice versa. 

Liberian coffee was gradually acclimatised to higher levels in 
Java by carrying seed a little higher at each generation. In Ceylon, 
when we tried to acclimatise the beautiful Cyperus Papyrus with 
European seed, we failed, but seed from India was a success. 

The whole question of correlation of characters is an extremely 
difficult one when looked at from the point of view of natural 
selection. If large, it implies that most of the characters con- 
cerned have no bearing upon natural selection, and do not 
interfere with the results produced by the modification in the 
first character, thus further implying that the change in that is 
sufficient to carry the new species past the line of mutual sterility 
that will usually divide it from the old. The characters of 
climbing plants had some evident connection, for all were useful 
in climbing, but that does not apply to the characters that one 
finds correlated in an ordinary species, which have no apparent 
connection of any kind, nor anything to which one can attach 
any adaptational value. Their best explanation seems to be that 
they have gone together in the apparently purposeless and un- 
accountable way in which characters in mutations so often seem 

to go. 


The mere fact that the prominent genera that occupy any kind 
of marked ecological standpoint, such as a bog, a saltmarsh, a 
mountain, a chalk-down, are usually the large and widespread 
genera, is enough to show that there was but little selection — 
they were the oldest and got there first, and being adaptable they 
became functionally modified to suit their new surroundings. 

What has been said about gradual adaptation applies equally 
to the view at present rather in favour that mutations were 
small, and that selection presently resulted in another small step, 
and so on. But what is to ensure that a small step in one direction 
shall be followed by a second, or that conditions shall continue 
to change in such a way as to make it worth while for such a 
thing to occur? 

The balance of probability would seem to be in favour of the 
appearance of structural characters by single mutations, and in 
that case it seems rather absurd to talk about adaptations in 
them. The adaptation is rather the internal and functional 

It would seem quite possible that climatic conditions all over 
the world have been gradually differentiating and becoming more 
varied as time has passed. On the whole, they have almost 
certainly become drier, though probably not in such places as 
many coastal regions. This would affect newly formed species by 
gradual^ restricting their freedom of movement, or even by 
forming impassable barriers. To move in a region of more or less 
uniform climate would probably require comparatively little of 
fresh adaptation to each new habitat, but if the climate were 
changing from one place to another, this adaptation would have 
to be greater, and would presumably need more time. This would 
in turn make the rate of travel slower, and it is quite possible 
that the change of climate might, so to speak, pass it upon the 
way, and erect a barrier some distance in front, the species 
reaching the limit of possible acclimatisation. This would seem 
to have happened in Ceylon, for example, where the island is 
rather sharply marked out into dry and wet zones. Comparatively 
few species are found on both sides of the divide, and really 
frequent in both zones. Many genera show a number of species 
in the wet zone with few in the dry, others the reverse, whilst of 
the genera that are confined to one zone, most occur in the wet. 

It is clear that it is somewhat stretching a point to say that 
new genera, arising locally, as we have seen will in all probability 
be the case, are adapted to wide spread over the world. As only 


rarely do the really large families show a single genus with the 
range of the whole family, a feature very common in small and 
frequent in medium-sized families, and as still more rarely does 
that genus in a large family show a species with the whole range 
of the genus, it is clear that any adaptation responsible for wide 
spread must be generic. What is much more probably the case, 
inasmuch as these widespread genera are admittedly of simple 
rather than of complex type, is that the parent of the genus still 
possesses great adaptability, or suitability to a considerable range 
of conditions. This will enable it to move far with less difficulty 
than usual, and as at the same time its structural evolution, which 
has probably little or no relation to adaptation, will be going on, 
it will give rise to more and more species. These will probably 
inherit their parent's general suitability to conditions, but it is 
quite probable that it may all the time be getting less (perhaps at 
each mutation), so that each new species may be liable to become 
more localised than its predecessor in regard to the total range 
possible to it, while at any given time it will of course be more 
local on account of its greater youth. 



In a paper on the floras of hill-tops in Ceylon, published in 
1908 (57), the author drew attention to the great proportion of 
local endemics — one-eighth of the total number of endemic 
species — that were to be found upon one only, or upon more than 
one, of the mountain tops of the south-west of Ceylon. The 
principal massif (the central) is to the south-west, a smaller to 
the north-east of it, and there are a number of more or less 
isolated peaks separate from them, the most isolated being Riti- 
gala in the north of the island (p. 24). The highest summit, 
Pedurutalagala, attains 8296 ft. ; Adam's Peak, the best known, 
is 7353 ft., and is rather isolated at the south-western edge of the 
central mass. There are ninety-seven well-marked Linnean species 
endemic upon these mountain tops, with eleven varieties of these 
or other species, some of which are usually reckoned as indepen- 
dent species. Of the species upon single mountain tops, there are 
no fewer than twelve upon Adam's Peak, which is so steep that 
its summit does not present any great area of vegetation for the 
last 2000 ft. 

Since the widely distributed species, those that were not en- 
demic to Ceylon, however localised in Ceylon they might be, were 
never confined to hill-tops, it was clear that there was, quite 
probably, some definite force or influence acting to cause these 
local endemics to exist in the places where they occurred. For a 
long time, opponents of my views maintained that they were 
relics of previous vegetation, and in fact this view is still popular. 
As they occur in general at higher levels than other species of their 
genera that are found in Ceylon, it was suggested that they had, so 
to speak, fled up the hills from their rivals. But if they could do 
this, they must have had a good capacity for internal, physio- 
logical adaptation, and it seems strange that they could not adapt 
themselves to staying where they were. And as most of the 
mountains rise from a central plateau, it seems very remarkable 
that so many of them should each be upon its own mountain. It 
seemed to me very probable that each was an endemic that had 
arisen upon the spot where it was found, and at various times, in 
conversation and elsewhere, I have suggested that the immediate 

62 ISOLATION [ch. vii 

mechanism of their formation might be the action of cosmic rays, 
which would be more marked at high elevations. 

It was clear that these mountain tops showed a distribution of 
plants like that which was shown by a group of islands forming 
an archipelago. Now the only thing obviously in common be- 
tween the two was isolation, and I therefore drew the conclusion 
that isolation as isolation favoured the production of new forms. 
At that time we knew little or nothing about the genes and 
chromosomes, and since then Harland has put forward the likely 
suggestion that long continued gene separation may lead to gene 
change, which of course in its turn might lead to definite mutation. 
Since about three-quarters of this mountain-top flora has no 
special adaptation for distribution by wind or by animals, it is 
highly probable that individuals of the more widely distributed 
species lower down would very rarely reach the higher summits, 
whose plants would be, and remain, very isolated. In this con- 
nection it is worth special notice that the islands which show con- 
siderable local endemism, like the Hawaiian islands, are very 
commonlv mountainous. 

Whether the mutation w^hich the author considers to have been 
the origin of any one of the species was due to one or the other 
cause, or to both, there would not be, in either case, any serious 
opening for gradual adaptation under the influence of natural 
selection. It must also be remembered that the number of indi- 
viduals is very small (cf. p. 25). In this connection, I may quote 
from Age and Area the footnote on p. 206: "A few days before 
I left Rio, Dr Lofgren found, on a little island about three miles 
off the coast, a new and very distinct Rhipsalis, of enormous size. 
He told me that there were only four examples on the island." 
I may also refer to the examples given in the same book on 
p. 151. 

Sixty-eight of the 108 endemics (including the eleven varieties) 
are found upon one mountain only, the other forty upon more 
than one. It is a very striking fact that these mountain endemics 
belong, not to small and local genera, but chiefly to large and 
widespread ones, as was shown on p. 26. 

The general conclusion from this piece of work is that isolation 
favours the development of new forms, and that local conditions 
have but little eff'ect in developing, though they may have much 
in determining the survival of, these new forms, and that conse- 
quently natural selection, upon adaptational grounds, is unlikely. 
It is more than doubtful whether any given species has been 

CH. vii] ISOLATION 63 

specially adapted to the exact local conditions in which it is 
found, except by the internal, physiological adaptation that must 
always be going on. It would be killed out at birth if not reason- 
ably well suited to the local conditions. 

Turrill (47) has shown that in the Balkans one may find pairs 
of altitudinally differing species like Bellis longifolia and sylvatica, 
a fact which affords further evidence in favour of the author's 
view that isolation and elevation, one or both, may lead to the 
formation of endemic species upon mountains. In Ceylon, of the 
sixty-two genera represented by endemic species upon mountain 
tops, forty-three also have endemics at lower elevations, and only 
nineteen have not, a fact which makes the supposition that 
those of high levels are relics seem a little far-fetched. 

The Podostemaceae as a family are very isolated, and they 
grow submerged in water, usually at what are only moderate 
elevations, yet they have many species. Though isolated from 
other plants, they usually cover their own habitat, the rocks, 
fairly thickly, so that one hesitates to suggest that they would 
have so many species were they really isolated as individuals. It 
would seem more likely in their case that they owe their numbers 
to the overhead force of plagiotropism that is always at work 
upon them. There are probably quite a number of causes that 
may lead to the formation of new species. 

Lakes formed by elevation of the coast of the Black Sea con- 
tain, I am assured, endemic species of cockles, a fact which would 
seem to favour isolation, especially as they are close to sea-level. 

Siparuna (p. 35) has the great bulk of its local species in the 
mountains rather than in the plains, and the same is the case with 
many other genera, whilst many of the isolated islands that 
contain so many endemics are also mountainous. These facts 
might seem in favour of elevation (cosmic rays) rather than isola- 
tion, but other plants, such as the Dipterocarps, show many 
endemic species in the plains, usually in dense forest. Here 
species formation is probably connected with age. 

Probably both isolation and elevation may be potent causes 
leading to well-marked development of new species. In the 
former case mutation is quite probably due to slow gene change, 
as Harland has suggested, but this would probably bring about 
sudden mutation by the adding up of strains until they became 
so strong as to cause some sudden kaleidoscopic change. In the 
latter case, if the cause of mutation be some effect of the bom- 
bardment of the genes by cosmic rays, one might expect the 

64 ISOLATION [ch. vii 

mutation to be sudden, and as most of the mountain endemics 
are well-marked Linnean species, it was perhaps very definite 
also, the principle of divergence of character coming into 

Another well-known series of facts is that families which are 
widely distributed chiefly or only in the more broken southern 
hemisphere, have rarely any genera that cover the whole of their 
area of distribution. In the plants that are more marked in the 
northern hemisphere, on the other hand, there is very often a 
genus that does cover the whole area, even if that also includes 
the southern hemisphere, such for example as Ranunculus^ 
Senecio, or Solanu7n. Whether this difference has anything to do 
with the isolation of so many areas in the south, we do not know, 
but the fact is suggestive. 

We are still very far indeed from any proper understanding of 
the operations that have been concerned in evolution, except 
that natural selection must evidently play a less conspicuous, or 
at any rate, a less direct part. It looks as if, more especially under 
certain circumstances such as elevation or isolation, evolution 
must go on, and this supposition is borne out by such things as 
the progressive change that shows in such plants as Stratiotes 
described by Miss Chandler (3), where a whole series of species 
differing in characters of no conceivable functional importance, 
have succeeded one another in successive geological horizons. If 
these changes had been a little more marked, we should have had 
two or more genera succeeding one another, and this point must 
always be borne in mind, together with the tendency to diver- 
gence, in considering extinct genera. 



VV ITH his customary scrupulous fairness, Darwin went out of 
his way to draw attention to an axiom of taxonomic botany that 
was seriously opposed to the theory of evolution by adaptation 
through the agency of natural selection. "Those classes and 
families which are the least complex in organisation are the most 
widely distributed, that is to say that they contain a larger pro- 
portion of widely distributed species. " Incidentally, as the 
simpler families must upon the whole be the older, this goes a 
good way towards proving the correctness of the theory of age 
and area. 

Now upon the theory of natural selection, it is clear that the 
successful genera must be those that have the largest numbers of 
species, or the widest distribution, or both; but as they have been 
developed by adaptive selection, they should surely on the whole 
be the most complex and specialised, showing the most signs of 
adaptation. This has always been a difficulty to the supporters of 
natural selection, and one which has been passed over with little 
remark. It can be at once explained by the hypothesis brought 
forward in Age and Area, for upon that the older forms will be 
the more widespread, and by reason of their age they must be 
the simpler on the whole, as having been more early formed in the 
process of evolution. But age and area is incompatible with the 
theory of natural selection. 

Age and area leads on directly to the theory which Guppy has 
called Differentiation, though a simpler and better descriptive 
term might perhaps be found — mutation perhaps, or differential 
or divergent mutation, for example, if it were admitted that 
mutations might be large. The essential feature of the theory, 
originally adumbrated by Geoffroy St Hilaire (41), is that evolu- 
tionary change goes downwards from the family towards the 
species, not in the opposite direction. A family begins as a family, 
and is not graduallv formed bv the destruction of intermediates. 
At the same time, of course, when it begins it is also a genus and 
a species, which at the start are all-important to the family; if the 
species be killed out, the family disappears. As it grows, the single 
genera and species become less important to it. The name 



differentiation was given by Guppy (11), whose concept it was that 
in the far back days of damper and more uniform climate most of 
what are now the large (or widespread, or both) families were 
formed, each at one stroke by well-marked mutations, and they 
then slowly began to grow in size by further mutations. As time 
went on, and the earth perhaps became drier on the whole, the 
variety of climate would increase, and mutations perhaps be 
more rapid, but their "size" is supposed to have become less, so 
that fewer great divisions, like for example the Monocotyledons, 
tended to appear. As differentiation went on in the climates, so 
it went on in the living forms. This does not mean that they were 
necessarily formed in adaptation to the climates but rather 
perhaps that the climatic change gave the stimulus which resulted 
in further mutations. Mutations might be of any rank, from 
variety up to division, so that any difference might appear at one 
stroke. If the newly formed plant could pass through the sieve 
of natural selection, and escape the dangers that threatened its 
very existence when it first began, it might then begin to spread, 
and once established in several places it would be, comparatively 
speaking, safe. As the original species thus survived as well as 
the offspring, the family must necessarily increase in number in 
such a way that when plotted by their numbers of species, its 
genera would form the "hollow" curve. It is quite possible 
that after a certain lapse of time a species 77iust die out (43), 
and it is still more possible that it may change into another by 
some simultaneous mutation. We have seen a small instance of 
simultaneous mutation in the sudden loss of smell that happened 
to all the plants of musk some years ago, and may perhaps see 
the results of series of such mutations in the consecutive species 
of Stratiotes described by Miss Chandler (3) and other such 

While under natural selection new forms only arise as the 
result of improvements in adaptation, under differentiation they 
arise because evolution must go on, at any rate whenever the 
needful stimuli, or conditions, are present, as we have seen in the 
case of the Podostemaceae (p. 20). Under natural selection the 
small variety becomes a larger one, and so on. It seems to the 
writer, as it did to Dr Guppy, that in trying to make evolution 
work in this way, people have been trying to work it backwards, 
and it is with the object of showing the necessity of proper 
revision of the current view that the present book is written. 
A number of more or less crucial test cases are given below, all of 


which seem to point to the supposition that differentiation gives 
a more correct picture of the direction of movement of evolu- 
tionary change than does natural selection, even though we have 
no clear vision of the mechanism that was involved in making the 
changes that occurred. 

The family is supposed to have arisen by some well-marked 
and sudden mutation (or conceivably a series of smaller ones, 
probably at close intervals), which would at one stroke change 
two or more characters and pass the line of mutual sterility that 
commonly divides species from one another. As the characters 
that divide the families are, after all, not so very numerous 
(cf. Appendix I) each family must take a different combination, 
sometimes taking one of a given pair, sometimes the other, and 
in every kind of mixture. Many families, for example, have 
alternate rather than opposite leaves, or superior rather than 
inferior ovary, but only the Cruciferae have alternate exstipulate 
leaves, bractless racemes of ^ regular flowers, sepals in two whorls 
of two, four petals, two short and four long stamens, superior 
ovary of two carpels, unilocular with replum, a pod-like fruit, 
and exalbuminous seeds. As the characters run in contrasted 
pairs (or triads), we have no information as to whether there is 
any advantage in one side rather than the other, or in either as 
against any possible intermediate, or indeed that any has any 
adaptational value. There is thus no evidence to show in which 
direction evolution moved, and we are perfectly free to select 
that for which we think that the evidence is better. It is this 
evidence, or rather, some of it, which we propose to bring forward 

Nor can we say with any likelihood of accuracy that the 
change indicated in any one pair is larger than that in another. 
Is it a greater change from two cotyledons to one than from 
alternate to opposite leaves? We do not know; all we have to go 
upon is that the latter is much more common. With one or two 
rare exceptions, there is no difficulty in supposing all Mono- 
cotyledons to have descended from at most a few different 
ancestors, whilst one may find alternate and opposite leaves side 
by side in many cases of allied genera or species. There is nothing 
inherently absurd in the idea that a family might be founded by 
a single mutation. 

About 1902 the writer became a convert to the theory of 
mutation, but it seemed to him completely illogical to insist that 
mutation could only be very small, when before us, in every 



family, there lay so much evidence that species, genera, tribes, 
sub-families and families were so continually separated by such 
well-marked divergent characters as leaves opposite or alternate, 
anthers opening by slits or by pores, ovules l-2-oo in each 
loculus, raphe dorsal or ventral, and many more such differences, 
which allowed of no intermediate or transition forms upon 
which natural selection might operate, which were such that one 
could not conceive of natural selection choosing between them, 
and which were so constant in their inorphological character — a 
feature that one could not expect natural selection to bring forth. 
They could only, it would appear, be the result of definite single 
mutations, and therefore mutations must at times be large. And 
if large in regard to these characters, which are very often of 
"family" rank, why not in all cases? 

In May 1907, without having seen Dr Guppy's book, the 
author published what was essentially the same theory (70), 
largely based upon the study of the Podostemaceae, and upon 
ten years' experience of tropical vegetation. Both authors were 
convinced that the great importance at that time attributed to 
adaptation was exaggerated. Natural selection was trying to 
construct a tree from the twigs downwards. But though a tree 
grows from the ground upwards, it always has young twigs and 
leaves (which may be looked upon as representing genera and 
species), though each one, when the tree is small, has a much 
greater value in proportion to the whole organism than when the 
tree is large. It seemed to us clear that in trying to show that 
evolution proceeded in the order 

Small variety — Large — Species — Genus — etc. , 

people were trying to make it work backwards, and that the 
proper order was 

Family — Tribe — Genus — Species — Variety. 

The relative rank of these groups varied as time went on. When 
very young, the family, the genus, and the species were the same, 
but as the family grew in size (just as with the tree mentioned 
above) the species became of less and less relative rank when 
compared to it. 

To turn to geographical distribution; upon the theory of 
natural selection, the large and widely distributed genera are the 
successes, the small and local the failures or relics. The success 
was always put down to better adaptation to conditions, though 
no one tried to explain how a species that derived its adaptation. 


say, in Europe, was able to spread as far as New Zealand. It 
could not become, in Europe, adapted to the conditions of New 
Zealand, and its appearance there must be due simply to the 
chance that the conditions resembled one another in both places, 
and that there were conditions in between that were not dissimilar 
at the time that the plant reached them. There can be no doubt 
that as a plant moves very slowly about the world, it can become 
adapted as it moves to the slightly different conditions that occur 
at each move. If it come to a place where the change is too 
sudden for it to adapt itself, it will then have come against a 
barrier to further spread — an ecological or a climatic barrier, to 
be added to the barriers of physical nature, such as high moun- 
tains, or open seas, that so often occur. By the formation of one 
of these barriers after the plant has passed, the distribution of a 
species may become discontinuous. 

The success of a species under natural selection means usually 
the greater or less extermination of the one from which it 
descended, and which was not so well adapted. Under the theory 
of differentiation, on the other hand, which goes with that of age 
and area, the large and " successful " genera are simply the oldest, 
while the small and local are in general the youngest. There is no 
special adaptational reason for size or spread, so that, within any 
close circle of relationship (which will more or less ensure the 
same general reactions to the outside world), the rate of spread of 
two or more forms will not usually be widely different. This is the 
essence of the theory put forward in Age and Area. 

In diagram 7 we have indicated what we imagine to be the 
probable general course of evolution under the theory of dif- 
ferentiation. The family is represented at the start by a solitary 
monospecific genus A, which will throw off new forms by muta- 
tions. At first they will probably be produced very slowly indeed, 
but as A increases its numbers (and with them its area, thus 
probably coming under the stimulus of different conditions) will 
probably appear more rapidly. Whether the earliest mutations 
will be more often specific or generic we have no idea, but most 
probably a second genus B will be "thrown" before so very long 
a time. This will again begin slowly, and it will be a long time 
before it throws a new genus Bb, whereas A will probably throw 
its second new genus C before Bb appears. All this, of course, is 
dealing in averages, and we do not know that this particular B 
will necessarily be slower than A, though on the average the 
second genus will be behind the first throughout. On the average 




A, as the oldest genus, should have the greatest area and the 
greatest number of species, B the second, C the third, Bb probably 
the fourth, and so on, but only on averages. Whilst in Ranuncu- 
laceae Ranunculus has 325 species to 250 in Clematis, one would 
hesitate, and rightly so, to say that the former was the older, when 
one remembers that it is herbaceous, and Clematis shrubby. 
As time goes on, it is clear that the rate at which new genera 

Fig. 7. Evolution by differentiation. Each genus is supposed to survive 

the whole way along the line at right angles to its origin, e.g. A still 

survives at H, B at Be, and so on. In order to save complication, the 

lines to show the gro^^i:h Bb, Be, &c. are not shown. 

are formed will increase. Each genus will begin with one species, 
and after a time will form more, so that the few older genera of 
the family will contain the greatest numbers of species. The result 
will be (cf. 66, p. 185) the gradual formation of the familiar 
hollow curve already described, with a few large genera of dif- 
ferent sizes at the top, and many monospecific genera at the 
bottom, the numbers increasing from top to bottom at an 
accelerating rate. As there will rarely, upon this theory, be any 
appreciable adaptational difference between species or even 
genera, there will be little or no reason why the older ones should 
be killed out (as there is under natural selection), and so the 
increase in numbers will lead inevitablv to the hollow curve. 


Up to the present, this theory is the only one which can make 
any pretence of explaining the hollow curve. The latter is so 
universal that it is evidentlv a general law which must be ex- 
plained. But it is, of course, in direct contradiction to the theory 
of natural selection. With the latter theorv one can make no 
predictions as to what may be found in the arrangement and 
characters of families, genera, or species. With differentiation 
one can make a beginning in this direction, and this alone makes 
a strong claim in its favour. 

If differentiation be the rule, it is clear that the ultimate result 
of the growth of a family from one original genus ^4 to a fair 
number of genera should in general be the formation of groups 
within groups, like the cat group or the dog group within the 
larger group of Mammals. By the principles of differentiation 
and of divergence of variation, each genus thrown will tend to be 
markedly different from the parent that throws it. If it were 
thrown very far back in the history of the famil}^ it will have 
had time to throw more (^enera in its turn. These mav, but so far 
as one can see, not necessarily must, display the character or 
characters that made their parental genus, B for example, dif- 
ferent from its own parent A upon the main line of the family. 
When these genera upon the second line B had become more or 
less numerous, or in any case if the characters of their parent had 
included two or more of the characters w^hich we usually rank as 
"family" characters, they would form a group Bh, Be, Bd, etc., 
well marked off from the first group which was being formed by 
the genera upon the main line. A, B, C, D, etc., and to these two 
groups we should probably give the rank of sub-families, or 
tribes, according to our conception of the value of their characters. 
One of these groups would most probably be larger and perhaps 
more widely dispersed than the other, and both would continue 
to grow and to spread. Supposing that the family escapes with- 
out very great damage all the various accidents that may befall 
it, and that all its genera behave fairly closely in the same way, 
as would be the case under differentiation, the original parent A 
will have the largest number of species (theoretically) and the 
largest area of occupation, while the other genera, B, C, etc., 
will be successively smaller in these respects, as we have seen 
in the ^Monimiaceae for example. The difficulty in defining what 
is or is not a sub-family or a tribe is the same as that of defining 
a genus or a species. We have no standard to work by in defining 
the value of a certain character, other than the way in which it 


appears in the group under consideration. Ruminate endosperm 
being characteristic of all Annonaceae, and of none of the allied 
Magnoliaceae, becomes very important in regard to these two 
families, while in the palms, etc., it may characterise some only 
of the species of a genus. Upon the theory of differentiation this, 
of course, simply means that in the one case the ancestor that 
showed it was the ancestor of a whole family, in the other only 
of a few species. Any of those characters which we usually con- 
sider as especially "family" characters may appear at any stage 
from family down to species, but on the whole are more common 
as one goes upwards in a family from the species. 

One thing that is always brought up as an argument against 
those who object to the explanation of evolution by natural selec- 
tion is that the fossil records show many extinct genera, of 
families still existing. The theory of natural selection, based upon 
adaptation, with its prompt killing out of less-adapted ancestors, 
accounts easily for this, while differentiation, which supposes the 
ancestors to live on together with their descendants, cannot do so. 
But one is apt to forget that the explanations of the facts of 
palaeobotany have for many years been such as could be made to 
jfit with the all-powerful theory of selection. One is reminded of 
the defence of phrenology in The Professor at the Breakfast Table. 
There are a number of things that must be taken into considera- 
tion before one can fully explain the fossil records. 

In the first place, it seems not impossible, as Small has shown 
(43), that there may be a definite limit to the life of species and 
genera. In his summary he says: "From this the important de- 
duction can be made that species die a normal death, presumably 
from the senescent sterility of old age, with, perhaps, a minor 
part being played by the progressive restriction of survival condi- 
tions for a senescent species . . . the species number in a genus is 
shown to follow the series 


This gives 24 million years as the normal lifetime of an 
ordinary genus." 

This is supported by such facts as those brought out by Miss 
Chandler (3), who found in different recent horizons a whole 
series of fossil species of Stratiotes, differing structurally from one 
another, but with nothing to which one could possibly attribute 
any adaptational value. The loss of smell by musk (p. 66) shows 
that a whole species can undergo a simultaneous change ; a larger 


mutation than this might have changed the whole of it to another 
species. Then again, if a geological catastrophe come along, it 
may easily destroy a whole species, or even genus, that has not 
yet been able to spread far enough to get beyond its range. Unless 
a fossil is found to cover such an area that it is unlikely that such 
a fate may have overtaken its living representatives, it seems to 
the writer in the highest degree unsafe to look upon it as an 
ancestral form of existing species. It is more likely to be a lateral 
mutation thrown off from the main line, and exterminated as a 
genus by some happening. 

Lastly, there should be mentioned the all but complete absence 
of transition stages in the fossils, a fact which violently disagrees 
with the supposition that evolution was gradual and continuous. 



1 T has long been known, though it has excited but little interest^ 
that there is a great tendency in variation to be divergent. As 
Guppy says (66, p. 104) Hooker, in his lecture upon Insular 
Floras, "shadowed out a general notion of Centrifugal Variation 
operating through countless ages'. It appears almost as a sug- 
gestion, but the idea had been evidently floating half-formed in 
his mind ever since he wrote his essay on the Tasmanian flora in 
the late 'fifties. It was the nucleus of a theory of Divergence or 
Differentiation that acquired more definite outlines as time went 
on, since it reappears in the intensely interesting account of a talk 
with Darwin which is given in a letter to Huxley in 1888 (19, 
n, p. 306). 

" We can perhaps understand the long intervals of time now. 
For the confirmation that such a theorv would have derived 
from a line of research instituted on Darwin's lines was denied 
to him. The two proved to be incompatible. For no inductive 
process based on Darwin's lines could have found its goal in 
a theory of centrifugal variation. 'I well remember', Hooker 
describes in a letter to Huxlev in 1888, 'the worrv which that 
tendency to divergence caused him (Darwin). I believe I first 
pointed the defect out to him, at least I insisted from the first 
on his entertaining a crude idea which held that variation was 
a centrifugal force, whether it resulted in species or not.' Huxley 
was in the same case. For he held views of the general differen- 
tiation of types, and his road that would lead to the discovery 
of the causes of evolution started from the Darwinian position. 
That road was barred to him." 

There can be no doubt, when one looks at the various characters 
that are used in taxonomic distinction between one form and 
another, that the bulk of them are divergent, and that the more 
so the higher one goes in the tables of characters, upwards from 
species to families. Take for example the list of "family" 
characters given in Appendix I, and note the great proportion of 
distinctions in which there cannot even be an intermediate, by 
reason of the marked divergence, and where, in any case, there 
can be no functional difference between the intermediate and the 


two extremes. For instance, among the characters will be found 
the following: 

Root tap or adventitious 
Stem monopodia! or sympodial 
Leaves alternate or opposite 
simple or compound 
palmate or pinnate 
parallel or net veined 
Inflorescence racemose or cymose 
Flower spiral or cyclic 

mon- or di-oecious 
iso- or hetero-merous 
regular or zygomorphic 
Receptacle above or below calyx 
Parts of flower in 2s, 3s, 4s, 5s, etc. 
Calyx in one or two whorls 
Odd sepal anterior or posterior 
Corolla free or united 

imbricate, valvate, or convolute 
alternate with, or superposed to, sepals 
Stamens in one, two, or more whorls 

diplostemonous or obdiplostemonous 
free or united 
Anther versatile or not 

opening by slits, pores, valves, etc. 
Pollen in various patterns of cell wall 
Carpels free or united 

1 to 00 

transverse or anterojDOsterior 
Placentation parietal, axile, etc. 
Raphe ventral or dorsal 
Micropyle up or down 
Style basal or terminal 
Stigma capitate or lobed 

Fruit achene, follicle, capsule, drupe, berry, etc. 
Seed with or without endosperm 

one, few, or many 
Embryo straight, curved, twisted, etc. 

and many more equally divergent, whilst in the few cases where 
intermediates are possible, no functional value or disadvantage 
can be read, either into them or into one of the extreme diver- 
gents. In no case, in these family characters, has any functional 
value been shown, in a definite and unmistakable manner, 
though suggestions have been made in one or two cases. 

If now one go on to the characters used in the keys which 
determine the genus and species of a plant belonging to one of 


these families, one finds the same kind of divergences, more and 
more marked on the whole in approaching the top of the list (the 
first divisions in the keys), and least marked in the characters 
that distinguish one species from another. This fact of increasing 
divergence as one gets nearer to the top of the list has always 
been a great difficulty in the path of the supporters of natural 
selection, and has been left discreetly unmentioned by them. 

Opening a volume of Engler, the family displayed is the Cyclan- 
thaceae, composed of six genera only. The first and most obvious 
division, into Carludoviceae with male flowers in fours, and 
Cyclantheae with male and female flowers in alternating rings or 
spirals, picks out the two most important genera, one in each of 
the groups, though the first group, with five genera and forty-five 
species, is much larger than the second, with one and four. 
IncidentaUy, how did selection, or gradual adaptation, produce 
these two very distinct types of inflorescence, and what was 
intermediate between them? Taking first the Carludoviceae, the 
genus Ludovia, with two species in Guiana and Amazonas, is 
first cut off*, having only a rudimentary perianth in the male 
flower (why, on the theory of selection, did it spoil its attractive- 
ness to insects?). The four genera left are divided into Carlu- 
dovica, which has forty species covering the whole range of the 
family in tropical America (north and south) and the West 
Indies, and which has a short perianth in the female flower, 
against a long one in the other three (again, attractiveness 
apparently spoiled), and an inferior ovary against a superior. 
Carludovica is by far the largest genus in the family, far out- 
numbering all the rest put together, and has a distribution 
covering that of the whole family, just as we have seen to be a 
general rule (p. 64). Does it owe its "success" to its inferior 
ovary, and if so, wherein does the advantage lie, for the flowers 
are so crowded that one cannot tell from the outside that the 
ovary is inferior? And if there is an advantage there, what about 
the reduced perianth? 

Evodianthus, next, is distinguished from the two other genera 
by having the stamens inserted in the tube of the perianth, while 
the others have them on the disk ; and finally Stelestylis has the 
stalk of the male perianth flat and hollow, and a pyramidal style, 
while Sarcinanthus has the male perianth forming six-sided 
pyramids, and no style. All three are small and little dispersed 
genera with two species in Costa Rica and the West Indies, one 
in eastern Brazil, and one in Costa Rica, respectively. 


Cyclantheae has only one genus, Cyclanthus, with four species 
in tropical South America from Peru northwards, and in the 
West Indies. It is thus the second genus of the family both in 
number of species and in dispersal, but as it is so much smaller 
than Carludovica, we must suppose that it was only cut off from 
that genus rather late. Its dispersal is much smaller than that of 

There is no reason for supposing the small genera to be relics; 
it is far simpler to imagine them all split off by large mutations 
from Carludovica in its gradual dispersal over the whole area of 
the family. The first split probably gave Cyclanthus, which is the 
second largest genus, and has a division to itself in the family, 
whilst it would seem extremely probable that the mutation that 
gave rise to it was an extra "large'" one, for the difference is so 
great between it and the rest. The other four genera, smaller, and 
with less distribution, count in the same group with Carludovica, 
from which they are not so markedly different. The general im- 
pression that one gains here, as in almost all cases, is that after 
the big mutation which first gave rise to the family, there follow^ed 
others which gradually became less and less marked, and which 
kept more or less closely wathin the boundaries that were indi- 
cated by the first mutation that occurred after the formation of 
the family. 

The first impulse of many will be to say that Cyclanthaceae 
form an exceptional famil}^ and perhaps also to say that the keys 
are artificial things. But the exceptional families, and the diver- 
gences that are shown in the keys, have both to be explained by 
natural selection, or by any other theory of evolution, just as 
much as have the ordinary families and the smallest divergences. 
Natural selection would be very hardly pressed to find any ex- 
planation of the very remarkable differences between Carludovica 
and Cyclanthus, especially as it is all but impossible even to 
imagine that there can be any intermediate stages, and no use- 
value can be put to either of the extremes or to any conceivable 

This supposition, that the first mutation, in a family newly 
formed by a large change from some ancestral form, may be in 
turn large, is well supported by an examination of the keys to the 
various families that are given in any general text-book of 
systematic botany. In the list in Appendix II, I have extracted 
from the keys in my Dictionary, 6th ed. (which are mostly taken 
from the Natiirlichen Pflanzenfamilien), the first dichotomy in 


each case, omitting a few keys where the first break is into three 
or more. These sixty famihes of course were selected for the 
Dictionary as being the larger or more important, and we shall 
go on to deal with the smaller ones below. 

It will be seen at once that these are characters the bulk of 
which are of the same rank as the "family" characters given in 
Appendix I. To take a few examples, one finds among them such 
character-pairs as these, which can all be matched in the family 
characters : 

1. Leaves opposite — alternate Gentianaceae 

2. Leaves in two ranks — not Musaceae 

3. Inflorescence racemose — cymose Verbenaceae 

4. Flower naked — with perianth Betulaceae 

5. Perianth actinomorphic — zygomorphic Campanulaceae 

6. Calyx polysepalous — gamosepalous Caryophyllaceae 

7. Calyx valvate — imbricate Mimoseae (Legum.) 

8. Stamens free — in tube Meliaceae 

9. Stamens two — one Orchidaceae 

10. Carpels free — united Annonaceae 

11. Carpels six to fifteen — three to five Hydrocharitaceae 

12. Ovule one per loculus — two Euphorbiaceae 

13. Fruit a berry — loculicidal capsule — 

septicidal capsule Ericaceae 

14. Fruit many-seeded — one-seeded Myrsinaceae 

15. Fruit achene — follicle Ranunculaceae 

Incidentally, how does natural selection account for, or explain, 
the difi'erences shown in 2, 3, 6, 7, 9, 11, 12, 13, 14, 15, to say 
nothing of the others? 

If one go on to the second dichotomy in a key to a big family, 
one finds that there are on the whole fewer, though still some, of 
the "family" differences shown, but these become less frequent 
in proportion to the total, as one goes down the list. 

It might be thought, perhaps, that small families would show 
a diff'erence from the larger ones, possibly in having smaller 
divergences in their classification into genera. If they were really 
relics, as they are often supposed to be, this might be the case, 
but in actual fact it is not found, as a glance at Appendix III will 
show. This contains the distinguishing characters of the genera in 
the families that contain two only. Here again one finds such 
distinctions as: 

Leaves opposite — alternate Caryocaraceae 



Perianth five — four Achatocarpaceae 

Flower 5-nierous — 3-merous Limnanthaceae 

K and C alternate — superposed Caricaceae 

Corolla valvate — convolute Quiinaceae 

Corolla free — united Xyridaceae 

Stamens few — oo Salicaceae 

Carpels two — three Balanopsidaceae 

Capsule — berry Balsaminaceae 


It is clear that in these small families the first split, which is 
only into two genera, shows just as important divergences as does 
the first split in the large families, which is into two sub-families, 
and the two genera of the small family are just as well separated 
as are the two (average) largest genera of the big family, which 
head its two chief sub-groups. The importance of this fact we shall 
better appreciate when we return to its discussion in the Test 
Cases (below, p. 112). If small families really consisted of relics, 
one would not expect that their genera should be divided by 
divergences of any special size, and certainly not that the diver- 
gences would be of the size and forin that one expects to find 
between the sub-families of large families, or even between the 
large families themselves. 

If one take a number of monotypic families, or families of one 
genus, from the first edition of Engler, and look at the distinc- 
tions there given for dividing the species of each of the genera 
into two chief groups, one finds these characters to be of some 
systematic importance, and often to be characters that are not, or 
hardly, capable of having intermediates. It is very hard to see 
how characters of such divergence should be those supposed to 
be left in the genera that survive of what is supposed to be a 
dying family. Here are a few examples : 

Monocotyledons . 

Typhaceae. Fruit with longitudinal groove, and open- 

ing in water; seed not united to fruit 
Fruit without groove, not opening in water; 
seed united to fruit wall. 

Sparganiaceae. Inflorescence branched. 

Inflorescence not branched. 

Naiadaceae. Dioecious. Stem and back of leaf spiny. 

Testa of manv lavers of cells. 
Monoecious. Stem and back of leaf not 
spiny. Three layers. 


Cannaceae. Three outer staminodes separate. 

Two outer united, third free. 

Casuarinaceae. Twigs whorled, rarely 4-angled, and then 

hairy in fork. 
Twigs not whorled, or 4-angled with whorls 
of four leaves. 

Myricaceae. Female flower with two to four or more 

bracteoles, not accrescent to fruit. 
Female flower wdth two lateral bracteoles, 
accrescent to fruit, making two wings. 

Myzodendraceae. Male flower with two stamens. 

Male flower with three stamens. 

Grubbiaceae. Flowers in threes in axils of foliage leaves. 

Fruit hairy. 
Flowers in threes in axils of opposite bracts. 
Fruit not hairv. 

Ceratophyllaceae. Fruit without spines or wings. 

Fruit with spines or wrings. 

Moringaceae. Seed without wings. 

Seed with wings. 

Nepenthaceae. Seeds egg-shaped with no appendages. 

Seeds with long hairlike coat. 

Myrothamnaceae. Two bracteoles. Stamens free. 

No bracteoles. Stamens in column. 

Platanaceae. Leaves usually 5-nerved. 

Leaves usually 3-nerved. 

Both in the monotype and the ditype families it will be seen at 
once that the characters that distinguish the species in the one 
and the genera in the other, are of the " family " type rather than 
of the specific or generic type found in large families. And most 
often they allow of no intermediates. Nothing but divergent 
mutation will explain such things. 

It is fairly clear that the larger genera tend to head sub- 
families, or groups of whatever rank may be considered appro- 
priate in the family concerned. It will therefore be of interest to 
study one or two families in greater detail, and the first that 
comes up in a random choice is the Ranunculaceae. We shall 
expect, upon the theory of diff'erentiation or divergent mutation 
which we have been discussing, that the chief division in the key 
will usually lead to the two chief groups into which the family is 
divided, and that each of these will be headed by one of the two 


or three largest genera in the family. Of course, since we cannot 
be sure of what is the largest divergence, nor be sure that that 
divergence necessarily came first in the mutations, we shall not 
expect every family to show such a result with any certainty, 
though one may expect it to show more often than not. The im- 
portant point is that each sub-group should be headed by a com- 
paratively large genus. If the group be small in proportion to the 
family, the genus may be small in proportion to some of the 
largest genera of the family ; if large, one will expect its leading 
genus to be larger. 

We shall further expect to find the smaller genera practically 
all included in the key that is marked out by the first divergent 
mutation. That is to say, that we shall in general expect them to 
be grouped as satellites round the big genera, not. as one might 
expect if they were relics, in small and comparatively isolated 
groups, which need not necessarily be closely related to the big 
groups of the present day. We shall, therefore, expect the charac- 
ters of these small genera to be less and less marked the smaller 
(by the number of species in them) that they are, and to be, so to 
speak, squeezed in between the well-marked characters of the 
large genera. Real relics, on the other hand, would be more likely 
to be distinguished fairly clearly from their relatives of the same 
familv, bv characters that might even be as marked as those that 
show in the first or second dichotomy of the key. 

The Ranunculaceae, a family of medium size, not very much 
larger than the average size for all families, have seven genera 
that (in comparison with the rest of the family) we may call 
large, each one containing at least seventy-five species. There are 
nine of intermediate size with ten or more, but none exceeding 
twenty (figures some years old), and ten small with nine or less. 
This gap between the large and the intermediate genera is not an 
uncommon occurrence, especially in families of small and medium 
size, and should be well worth further investigation. 

The big genera are : 



to group 



N. temp. 








N. temp. 








N. temp. 








N. hemisphere 


Total 1180 or 87 per cent of the family 



The intermediate genera are : 



N. temp. 




N. temp. Old World 




N. temp, and Arctic 


C alt ha 






Eur., Medit. region 




N. temp. 




Eur., Medit. region 




Eur., Asia, W.N. Amer. 




N. temp, and Arctic 


Total 133 or 10 per cent of the family 

The small genera are: 







Mts. of Eur., C. Asia 


Er ant his 


N. temp. Old World 




Japan, China 

A 1 



Antarctic Amer. 




C. Asia 








N. temp. Asia and Amer. 




Japan, N. Amer. 




Atl. N. Amer. 


Total 43 or 3 per cent of the family 
Grand total 1356 spp. in 26 genera, average 


The classification used here is that of Engler and Prantl, in 
their first edition — Paeonieae (A 1) and Helleboreae (A 2) being 
marked off" from Anemoneae (B); Paeonieae have only two 
genera. Of the large genera given above, three belonging to 
group A 2 have an average of 133 species per genus, and are only 
North temperate in distribution, while four belong to group B, 
average 195, and are cosmopolitan in distribution in three cases, 
the fourth being only North hemisphere. On the face of it, by the 
greater size and greater distribution, B would appear to be an 
older group than A. The intermediate genera are intermediate 
both in size and in distribution, and the small genera are evidently 
the lowest in both respects. 

Now the very old and large genera, upon the theory of dif- 
ferentiation, must owe their origin to the earliest generic muta- 
tions in the family, and upon the principle of divergence of 
variation, we shall expect these variations to be, on the whole, the 
most divergent that occur in the family. In other words, the 
larger genera of a family should be separated by well-marked 
divergences, while the smaller will be less so. This is exactly what 


we do find. If we draw up a key to the Ranunculaceae, dealing 
only with the seven big genera given in the list above, it will be 
found to be just such a divergent key, so that to place a species 
in its proper genus is a very simple matter. Here is the whole 

A. Ovules on both sides of ventral nerve of carpel: follicle — 

Flower with 2 or (2) honey-leaves: 
Honey-leaves sessile, odd leaf of 

perianth spurred, projecting. Delphinium 

Honey-leaves stalked, odd leaf 

helmet-shaped, erect. Aconitum 

Flower with 5 honey-leaves. Aquilegia 

B. Ovule solitary at base of ventral nerve: achene — 

Ovule with one integument. 
Ovule pendulous: 

Leaves opposite. Clematis 

Leaves alternate (exc. involucre). Anemone 

Ovule erect. Ranunculus 

Ovule with two integuments. Thalictrum 

The key is a very simple affair, with widely divergent charac- 
ters at every stage, so that there can be no difficulty whatever in 
placing any species in its genus, were these the only genera in 
the family. It is only when the smaller genera are included that 
anv difficultv is found. With each new one that is added, the 
characters that have to be used become more numerous and more 
complicated. These seven large genera cover practically the whole 
range of variation that is found in the family, to say nothing of 
including 87 per cent of the whole, and the rest of the genera 
come within, or very close to, the range thus indicated. If one 
add to the seven large genera the rest of the family, which con- 
sists of small genera not exceeding twenty species, one finds that 
the steps which in the above key lead only to Ranunculus lead 
also to Myosurus, Oxygraj^his, Trautvetteria, and Hamadryas. 
A whole series of new steps in identification is now required, but 
the important and interesting point is that all the new additions 
come within the original key, or very nearly so. The new additions 
that have to be made to the lists of characters are all at the 
generic end of the key or close to it, with few exceptions. Instead 
of finding that '"ovule erect" leads straight to Ranunculus, we 
have to have a supplementary key like the following: 



(Ovule erect) 

Flower hermaphrodite. 

Fruit with no hard layer in wall. 

Ovule ultimately pendulous ; perianth 

leaves spurred. Myosurus 

Ovule always erect; perianth leaves 
not spurred: 
With honey-leaves. Oxygraphis 

Without honev-leaves. Trautvetteria 

Fruit with hard layer in wall. Ranunculus 

Flower dioecious. Hamadryas 

While almost all of the new and smaller (younger, according to 
age and area) genera that have to be added to the key that we 
obtained from the large (old) genera are added simply in such a 
way that they cluster around some of the big genera, like those 
just given cluster around Ranunculus, one finds every now and 
then one or more genera (usually clustered) which do not so 
obviously represent satellites of the big genera, but have a focal 
point of their own. Thus among the intermediate genera in 
Ranunculaceae there appears Paeonia, whose characters require 
a splitting of the early character of distinction given above and 
marked A. Instead of leading directly to Aquilegia, Delphinium, 
and Aconitum, as at present, A has now to include Paeonia, which 
cannot be easily split off, as was Ranunculus, by extension of the 
generic end of the key, but has to be split off as follows : 

A: Follicle, etc. 

Outer integument of ovule longer than inner; Paeonia 

no honev-leaves; ovarv wall fleshv. 
Outer integument not longer, sometimes one Aquilegia, etc., 

integument only; honey-leaves or not; as before 

ovary wall rarely fleshy. 

Passing yet further down the scale of genus-size, Paeonia 
becomes accompanied by Glaucidium, with two species in the 
mountains of Japan and China (a much smaller distribution than 
that of Paeonia, as one would expect upon age and area). As 
the separation of Paeonia was so comparatively high up in the 
scale, this small group of two genera is evidently of somewhat 
different rank from that which surrounds Ranunculus, and is 
often regarded as a sub-family; but it is important to notice that 
it is hardly of the rank of the other two sub-families. As a key 
to the three sub-families, we have 


A. Ovules on both sides of ventral nerve; follicle — 

(1) Outer integument of ovule Sub-fam. I. Paeonieae 


(2) Outer integument of ovule Sub-fam. II. Helleboreae 

not longer. 

B. Ovule solitary at base ventral Sub-fam. III. Anemoneae 

nerve; achene. 

As Paeonia is comparatively small, it is extremely probable that 
it is much vouno-er than the Helleboreae, which include three of 
the first seven very large genera; and this is confirmed by its 
small distribution as compared with them. 

It is clear that if we suppose the big genera of a family to be 
the first formed, and that by the most divergent variation that 
(on the whole) occurs in the family, whilst the intermediate and 
smaller genera are younger, we can get a satisfactory picture of 
what seems to have gone on. The big genera, formed by early and 
divergent variation, mark out the outer limits (or nearly so) of 
the familv, the intermediate and small ones, which are on the 
whole the younger, coming later and filling in the outline thus 
made. In the later stages of the family, the divergences tend to 
become smaller and smaller, especially as the possibilities of large 
divergences have become somewhat used up. At each stage the 
divergence is probably limited by what has already occurred, and 
with comparatively few exceptions keeps within the limits thus 
marked out. If, as in Annonaceae, the commencing mutation, 
which gave rise to the family, includes a berry fruit, then this may 
be a family character; if, as in Myrtaceae, it is produced in the 
second mutation, the berry may characterise the sub-family 
resulting from that. It may even be produced in later and later 
mutations, and be the mark only of a tribe, a sub-tribe, a group 
of genera, a single genus, or it may even mark only some of the 
species in a genus. 

The key to a family, if well constructed, in all likelihood gives 
a clue to the mutations by which that family evolved into its 
present condition. But one must remember that while a group of 
the largest genera will doubtless be older than a similar group of 
smaller ones in the same family, those that are actually largest, 
or those that are the most widely distributed, need not necessarily 
be the oldest, for there are so many accidents that may befall 
plants in the shape of geological and other changes. Once a genus 
becomes so large and important that it has many species and 


covers great areas, the chances of its complete disappearance, 
unless mere age, or further (probably universal) mutation can do 
it, are small. The intermediate genera, on the other hand, may 
often have suffered complete extinction, and still more the 
smallest genera. 

What has been said is also strongly supported by the facts of 
distribution. There can be no doubt that in any given family, the 
distribution of the genera goes on the whole with their size, as 
has been shown in Age and Area, chap, xii, p. 113 (Size and 
Space). Age, size of genus, and area occupied by it, all go 

It is clear that this analysis of the Ranunculaceae fully sup- 
ports the theory of differentiation as against that of natural 
selection, upon which no prediction can possibly be made as to 
the size or composition of a family. 

As another example, let us take the sub-family Silenoideae in 
the Caryophyllaceae. It contains eighteen genera, whose numbers 
of species, from the latest monograph (35), where the numbers in 
the large genera are evidently rounded off, are 

400, 300, 90, 80, 30, 30, 25, 10, 8, 7, 5, 5, 4, 4, 4, 1, 1, 1. 

The first two genera, Silene (400) and Dianthus (300), which 
contain 700 out of the total number of 1005 species in the sub- 
family, are instantly picked out (supposing these to be the only 
genera in the group) by the very first dichotomy that is given in 
the key, which splits the Silenoideae into two tribes. All the 
Lychnideae, headed by Silene, show a calyx with commissural 
ribs; the Diantheae, headed by Dianthus, not so. The other 
Lychnideae contain 80, 10, 8, 7, 5, 5, 4, 1, 1 species, and the other 
Diantheae show 90, 30, 30, 25, 4, 4, 1, adding up, the one to 121 
species, the other to 184, or in both cases much fewer than in the 
big genus at the head of the group (400-121 and 300-184). Each 
tribe is headed by a big genus, and the one tribe adds up to 521, 
the other to 484, showing a difference just as indicated in Test 
Case II, p. 94. The figures seem to indicate that in the Diantheae 
there were more genera produced of intermediate size, so that 
perhaps the stimulus of genus formation came earlier, and 
resulted in the greater number of species shown by the smaller 
Diantheae than by the smaller Lychnideae. 

As the divergence just considered includes all the Silenoideae 
on one side or the other, it is not unlikely that it was the first 
mutation to appear after the first formation of the group by the 


mutation that produced Silene itself. All later mutations come 
within it, in the sense that the effects of this first mutation are 
shown in them all. If we now follow only the tribe Lvchnideae, 
Pax's key next splits off, by triple (or more probably by two 
separate) divergences two genera, Ciicubalus, with one species in 
Eurasia, and with berry fruit, and Drypis, with one species in 
south-east Europe, and with capsule with lid; but as these are 
small and rather local genera, and could evidently be split off 
from any genus with a capsule, it is unlikely that they were 
formed at this early stage. The next division in the key is more 
probably that which split off Melandrium with eighty species in 
the northern hemisphere. South Africa, and South America, 
which differs from Silene by its fully unilocular capsule as against 
a capsule multilocular at the base. In view of the great dispersal 
of Melandrium, it is by no means improbable that it may have 
been formed even earlier than Dianthns, and having met with 
greater vicissitudes, such as the separation of Old and New 
Worlds, has lost many more species than either Silene or Dian- 
thus. In both Melandrium and Silene the capsule has two teeth 
to a carpel, and each has a closely related genus with one tooth 
per carpel, which was probably split off later {Viscaria near 
Silene, Lychnis near Melandrium). Further mutations might give 
the two genera Uebelinia and Agrostemma near to Melandrium, 
by changing the relative position of carpels and calyx segments, 
which are opposite in Melandrium and alternate in the two small 
genera — a change which could only come by some mutation. They 
might also give Heliosperma as a mutation from Melandrium, it 
having only two rows of papillae on the seed, instead of having 
them all over, and Petrocoptis as a mutation from Lychnis, the 
latter having the teeth of the carpel twice as many as the styles, 
the former once. It will be noticed that this phenomenon appears 
(in Silenoideae-Lychnideae) in two places, and must have 
appeared independently in these two, though the morphology 
or the structural features are the same in each case. 




JL T is now almost unquestioned that existing plants and animals 
have been produced by an evolution that, on the whole, has gone 
forward, producing organisms of increasing complexity such as 
man and the higher animals and plants. But many of the " lower " 
things, the seaweeds, the lichens, the smaller ferns, the insects, 
etc., have not been killed out, but have also increased very 
greatly in number. This has always been difficult to explain upon 
the current theory, but is perhaps more easy of explanation if we 
consider that evolution was not altogether a matter of con- 
tinuous improvement in adaptation, at any rate as indicated in 
external characters, which are almost the only things to show us 
that there has been any great evolution at all. 

We have seen that a good case can be made out for differen- 
tiation, in so far as it implies that a family most probably began 
(at one step) as one genus with one species, of family rank, giving 
rise later to other genera and species carrying the family characters 
(but often with modifications in various directions), and making 
in this way a family whose numbers would steadily increase, 
inasmuch as there was no necessary reason why any of them should 
die out, as there was under natural selection, which killed out the 
less well-adapted ancestors. The loss of this first species and 
genus would of course exterminate the family, but as it grew in 
size, the loss of one genus with one species would matter less and 
less, the rank of the genus with reference to the family becoming 
continually less, the smaller the genus in proportion to the size of 
the family. 

The adoption of the theory of differentiation of course turns 
the working of the mechanism of evolution the other way round, 
and in the opinion of the writer puts events in their proper 
sequence. It therefore seems clear that the first thing to be done 
is to decide which of the two views is the more correct one to 
take. Did evolution go in the direction from variety and species 
towards higher forms (Darwinism), or in the reverse way (Dif- 
ferentiation)? Did the family begin as a species of family rank, 
or was it gradually formed by the destruction of intermediates? 


We are still far from any understanding of the actual mechanism 
of evolution, but if we can feel sure of the direction in which it 
worked, we shall have made one step in advance which may open 
a way to profitable lines of research. 

For example, take the case of economic botany, with its back- 
ground of applied organic chemistry. So long as we imagine a 
plant A, producing a valuable substance a;, to be descended from 
some ancestor unknown, and quite probably unknowable, we are 
heavily handicapped in tracing the origin and chemistry of x. 
But if the descent, as differentiation would have it, were the 
other wav, and the actual ancestors of A mav still be alive, so 
that their chemistry may be studied, the work is greatly sim- 
plified. Instead of remaining a vast mass of facts with little or 
no co-ordination, economic botany may become a definitely 
scientific subject, producing knowledge, not merely supplying it 
in a dictionarv form, and we shall be able to look to valuable 
results as yet quite unforeseen. 

Endemic or local plants, again, if they be regarded as usually 
the youngest in their own circles of affinity, and therefore as 
"the latest thing" in breeding, in chemistry, etc., may become of 
great importance, instead of being regarded as practically 
negligible relics, as at present. 

The writer hopes that the work here described may aid in 
putting workers upon the right path towards a discovery of the 
actual mechanism of evolution, and it seems to him that it may 
be to cytology that we should look for the next step in advance. 
As yet, the mutations that have appeared seem usually to be 
lethal, recessive, or non-viable, but this is no proof that viable 
or dominant mutations cannot appear also. If the result of 
such a mutation were to be found growing anywhere, people 
would at present say that it was another relic, and leave it at 
that. Guppy has pointed out that many of the species that 
have been found once only, and have never been seen again in 
spite of search, are quite probably the result of such mutations, 
which were in the early stages of establishing themselves, and 
were perhaps exterminated by collecting specimens, or were not 
viable (cf. 66, p. 151). 

As the two theories of the direction of evolution are diametri- 
cally opposed, it seemed to the writer possible to devise some 
crucial tests between them. A number of these have been thought 
out from the principles laid down in Age and Area-, these sug- 
gested others, which have led to more. This simple fact, that these 
principles can be so extensively used for prediction, goes to show 

90 TEST CASES [ch. x 

their general correctness, for the rival theory of natural selection 
cannot be used to make predictions at all. All the evidence ob- 
tained seems to point in the same direction, and seems to show 
that evolution is moving as an ordered whole, upon lines that 
have an arithmetical or mathematical basis. The general mathe- 
matical propositions that underlie the theory that is here being 
put forward have been worked out fully by Mr G. Udny Yule, 
whose paper (75) contains a very readable and simple general 
introduction and summarv that should be read bv all who take 
any interest in the subject under discussion. 

The actual evolution of new genera and new species seems 
largely determined by a simple following, differing in speed in 
each individual case, of the law of continual doubling, as was 
shown by Yule and the author in 1922 (76). Sir James Jeans has 
said that "All the pictures which Science now draws of nature, 
and which alone seem capable of according with observational 
fact, are mathematical pictures." In this he was referring more 
especially to the physico-chemical sciences, but the work de- 
scribed here, and in Age and Area, gives the impression that 
biology will have to be added to them, though not in such a 
clearlv-cut condition. 

In this and the following chapters, some test cases are de- 
scribed, all giving evidence which seems not infrequently conclu- 
sive that the theory of differentiation, or divergent mutation, 
is a more probable explanation of evolution than is that of 
natural selection. The number of cases described may seem 
excessive to some, but the writer, w^ho is now growing old, has 
tried to make his position as secure as possible, and has therefore 
chosen a number of tests from various parts of the subject. 


It is admitted that as time has gone on, plants have increased 
vastly in number. But how did natural selection, working through 
gradual adaptation, produce such an increase? The very name 
selection would seem to imply the picking out of some from among 
many. One would expect the ultimate result to be a few "super- 
plants ", not a vast and increasing number with no evidence to 
show that any one was superior to its immediate relatives. 

On the theory of natural selection new variations, to have any 
chance of persistence, must have been produced so that acci- 
dentally or otherwise they suited the conditions, or more com- 


monly, some difference in the conditions, better than did their 
immediate ancestor, which must have been suited to the condi- 
tions to survive and reproduce. This would most probably mean 
some difference in the physical conditions, especially of climate 
or of soil, or in physical differences due to the presence of other 
organisms, such as greater shade, greater demand for some 
chemical constituent of the soil, or other thing. But ivhy should 
a change in soil, or in climate, or in biological surroundings, un- 
less perhaps it were very strongly marked, involve any morpho- 
logical change? It is very difficult to see any connection between 
these things. 

Unless by some accidental happening, or in the rare case of a 
"pure stand" — a solitary species occupying a large area — the 
surroundings made by other plants would be continually variable. 
Weather also is changeable, and unless a species were suited 
from its birth to this fact, it would have a very poor chance of 
survival in any case. Soil varies from one spot to another, and 
so on. Unless variation in the conditions went continuously 
in the same direction, as for example in a change of climate (not 
of weather), it is very difficult to see why variations in the 
morphological characters of the plant should go always in the 
same direction, as is required if they are to be added up to 
make specific differences. And it is difficult to see why, for 
example, there should be any need for change at all in a species 
that occurs, as do most species, principally in one association of 

But to get increasing numbers of species, one species must (at 
any rate very often) give rise to two or more, not simply to one 
new one, unless, as on the theory of differentiation, the parent 
survive as well as the offspring. But upon the theory of gradual 
adaptation, to get two or more species from one without losing 
them by intercrossing in the early stages, one must have dif- 
ferent conditions in different parts of the range of the same 
parent species. In other words, it must occupy a fairly large 
area to get into such variety, and this is the basis of the explana- 
tion of the local species as relics, though they far outnumber the 
widely distributed ones, even in the most "successful" genera. 

But if all the local species are failures, where does the increase 
in number come from? Even in his own diagram (6, p. 90) 
Darwin begins with eleven species, which at the next stage 
become reduced to seven, the rest disappearing. At an indefi- 
nitely later stage, shown in faint lines, they have increased to 

92 TEST CASES [ch. x 

fourteen. The relative proportions of widely and of narrowly 
distributed species were not well known at that time, nor the 
relative proportions of the genera in a family, both shown in the 
hollow curves. Nor was it realised that no boundary could be 
fixed dividing endemic species or genera from non-endemic. A 
mere glance at the hollow curves will show this, or at a contour 
map (chap, xiii, case 27). Even the big genera consist largely or 
even principally of local or endemic species. 

As an actual case, we may take the Monimiaceae, already de- 
scribed upon p. 33. There are two large genera and thirty small. 
What is selection going to do with these latter, which contain 
30, 25, 15, 15, 11, 7, 6, 5, 4, 4, 4, 3, 3, 3, 2, 2, 2, 2, 1, 1, 1, 1, 1, 
1, 1, 1, 1, 1, 1, 1, species respectively? The ones will presumably 
disappear first on the whole, and the family should logically be 
reduced ultimately to the two large genera of 107 and 75 species, 
most of which again are relics in the sense that they only occupy 
small areas. It is clear that natural selection, working upon the 
lines usuallv laid down for it, would result in a tremendous dimi- 
nution. And not only do the numbers of species in the genera 
follow the law of Age and Area — the hollow curves — but so do 
the areas that they occupy. The diameters of areas occupied by 
genera of one or two species average about 560 miles, with three 
to five species about 830, with six to eleven 1766, with fifteen to 
thirty about 2310, and the two large genera about 5500 miles. 
One can draw no lines of distinction. If the ultimate end of 
natural selection is to be a small number, why begin with so large 
a one? Whence did thev all come, and whv were thev evolved at 
all? Under differentiation expansion is the rule, for each one may 
ultimately give two, and there is no necessary reason for the 
older ones to die out as they must under natural selection. Once 
established in a small way, if there is no necessary difference in 
adaptational value between one morphological form and another 
nearly allied to it from which it may even have arisen, a species 
may go on indefinitely, though by reason of the presence of 
barriers to spread — physical, climatic, ecological, etc. — it may 
never be able to expand over very large areas of country. 

The same results as are shown by the Monimiaceae are shown 
by any other family that one may take, especially if it be of fairly 
reasonable size. The Cruciferae, with 350 genera, begin higher up 
(with larger genera than the Monimiaceae) and end with 56 twos 
and 145 ones. The Compositae end with 148 twos and 446 ones 
(old figures). 


It is difficult to understand, upon the theory of natural selec- 
tion, how the long tails of genera that contain only one or very 
few species, and that occur in all but the very smallest families 
(and are often indicated there), ever came to be evolved at all. 
Natural selection looks upon them as the failures, and upon the 
large genera with many species as the successes; the latter are 
also widely distributed about the world in practically all cases. 
But ivhy should a genus with many species occupy a large area? 
There must, upon the adaptation theory, have been in it a mar- 
vellous generic adaptation. If we take the first hundred genera in 
my Dictionary (5th ed.) with fifty or more species, half of them 
show a distribution right round the world, and at least half the 
remainder cover immense areas. The smallest ranges are those of 
Acantholimon (Eastern Mediterranean) and Agathosnia and Aloe 
(South Africa). But, with ranges like this, these large genera 
must be very old, to have reached so many continents before 
communications were broken, and how did thev come to find, in 
those early times, so great a variety of conditions as to lead to so 
many sjDecies, at a time when conditions are usually supposed to 
have been much more uniform than now? 

If the small genera of one or a very few species are to be looked 
upon as relics, why are there so many of them, and wh}^ do their 
numbers increase tow^ards the bottom? It was shown (in 66, 
p. 185) that out of 12,571 genera of flowering plants, 4853, or 
38-6 per cent, had only one species each, 12-9 per cent had two 
species, and 7-4 per cent had three. The numbers diminish up- 
wards, following the regular hollow curve, shown not only by the 
grand total, but by each individual family down to quite small 
ones. The larger the family, the more accurately does it show the 
hollow curve, a fact which does not favour the view that the tail 
of small genera is composed of relics. Why should a "successful" 
family have so many? One cannot draw a line through such a 
curve, and say that all on one side of it are to be looked upon as 
failures, on the other side as successes. To explain the curves, the 
selectionists are thus obliged to admit that natural selection 
shows its results in a continual and decreasing diminution of 
numbers, as indeed one would to some extent expect from its 
name. But if so, why did nature produce so many at first, only 
to cut them down later, and where does the increase in number 
come from, that is undoubtedly shown by the vegetable king- 
dom? Was there no selection in ancient times? Differentiation, 
on the other hand, as Yule has shown (75), necessarily results in 

94 TEST CASES [ch. x 

the production of genera in such a way that the result must be a 
hollow curve. 

The result of this first test is thus clearly in favour of dif- 


On the theory of natural selection, the parent of a new species 
will tend to become a relic, ultimately disappearing, but on that 
of differentiation, there is no necessary reason why this should 
happen. The parent may survive, probably does, long after the 
throwing of offspring that may be specifically or even generically 
distinct. As time goes on, the mutations in any one line seem to 
tend to become perhaps less marked, so that generic mutations 
perhaps become less frequent in proportion. It is possible that at 
first, when considerable divergence is more easy, all or most of the 
divergences may be what we should consider as generic. But on 
the whole, it is evident that in any case the earlier members of a 
family should be larger than the later ones — in numbers of 
species if genera, in area occupied if species. They started first, 
and on the average they should keep in front, so long as one con- 
siders only related forms growing in similar conditions, as already 
fully explained in Age and Area. The oldest genus in a family, 
therefore, should in general tend to be the largest genus in it, and 
the older and larger the family, the larger should its largest genus 
be. But we have no absolute test of age, and must not try to 
make comparisons of age, except between close relatives in 
similar conditions. To say that the largest genus in a quickly 
reproducing, mainly herbaceous family like the Compositae is older 
than, or even as old as, the (far smaller) largest genus in the slowly 
growing and reproducing giant trees of the Dipterocarpaceae, is 
to make a statement which has nothing whatever to back it. The 
latter, though only 5 per cent of the size of the first, may even be 
very much the older genus. All kinds of accidents also interfere 
with arithmetical regularity in these matters, so that it is really 
very astonishing to see how regular the figures are, in spite of all 
the geological or climatic changes, or other outside interferences. 
None the less, as has already been shown in Age and Area, 
p. 188, the supposition that the size of the largest genus goes with 
the size of the family (a fact which could not be predicted by the 
aid of natural selection) is borne out when one takes averages. 


The table given there shows this clearly, and some later figures 
show it equally well: 

ize of family in 




of the largest 

(not in species) 

genera in each (species) 



















The requirement of differentiation, that the size of the largest 
genus of the family shall go up with that of the family itself, is 
fully borne out, while no theory of natural selection or of gradual 
adaptation can offer any explanation of the facts. 


We may now consider the relative sizes of the genera in a family 
or other group. Upon the theory that they were formed by 
gradual adaptation one cannot say more about their probable 
relative sizes than that some (the ''successful" ones) will pro- 
bably be large, and some (the "failures'" or "relics'") small. Nor 
can one give even an indication of what their relative numbers 
will be. Further, one will also be inclined to expect to find some 
kind of distinction shown between the successes and the failures. 
But if differentiation be the more correct view to take, evolution 
is no longer of necessity a direct expression of continually im- 
proving adaptation, nor is the geographical distribution of plants. 
It is clear that if that be so, there would be little reason for one 
plant to spread, on the average, faster than its near relatives. 
All in a related group would tend to spread at a more or less 
uniform speed. But the speed of spread would depend upon 
many factors, and to average these out, as already explained in 
Age and Area, plants should only be taken in groups of say ten 
allied forms, which should only be compared with other tens 
allied to the first. Plants of systematic affinities that were widely 
different might spread at completely different speeds, or plants 
that differed in habit, like trees and herbs, or in speed of repro- 
duction or other things. But on averages, with groups of allies 
growing in fairly similar conditions, the oldest genus of a family 
should be the largest, whilst the others should show a continually 

96 TEST CASES [ch. x 

decreasing size, but increasing numbers, with decreasing age. The 
result would be to give one of the hollow curves which we have 
described above. A little thought will soon show that the diminu- 
tion in size will not be proportionate to that in age, for the older 
that a genus is the more rapidly will it tend to gain upon those 
younger than itself (66, p. 34), 

As a genus or species (they are the same at the start) increases 
in number of individuals and in area occupied, it w411 begin to 
"throw" offspring differing from itself, by mutations occurring 
at infrequent intervals, sometimes of generic rank, but more often 
of specific. The average size of a genus is about fourteen to fifteen 
species, but this does not mean, as one is tempted to suppose, that 
a generic mutation may occur once in fourteen to fifteen times. 
Rather it means that the average age of a genus may be more 
or less represented by the average age of those which possess 
fourteen to fifteen species. Some of the throws will be undoubted 
species, some undoubted genera, some again of doubtful rank. 

Supposing, which seems the most probable, that a new species 
or genus begins upon a small area, it will probably be a very long 
time before it occupies a more considerable space with more 
individual representatives. But while it may wait a very long 
time for the first throw, it would seem probable that the frequency 
of the throws will on the whole increase w4th the number of the 
individuals in the species, which in turn will tend to increase more 
and more rapidly as time goes on (cf. Age and Area, pp. 33-4). 
The first line of descent, that from the original genus (and species, 
of course) of the family, will always have the start of the second, 
which arises from the first generic throw of the original genus. 
But as time goes on, there will be a continually increasing number 
of lines of descent with the continual formation of more and more 
genera to head them, so that at last we shall get the familiar curve 
shown by any table of numbers of species in the genera of any 
particular family of reasonable size. Thus a recent enumeration 
of the Caryophyllacea^ (35) gives the following figures (bigger 
genera obviously rounded to nearest ten or more) : 

400, 300, 160, 100, 100, 90, 70, 40, 40, 30, 30, 30, 25, 23, 20, 
20, 20, 20, 20, 18, 16, 15, 12, 10, 10, 10, 8, 7, 6, 6, 6, 5, 5, 5, 
5, 4, 4, 4, 4, 4, 3, 3, 2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1. 

If, then, genera are formed upon this principle — and that this 
is quite a probable approximation to what really happens is 


shown by the universality of the hollow curve — we shall expect 
to find that there will be a gap between the numbers of species in 
the two largest genera of the family. This gap will obviously be 
due to the fact that the two first genera of a family will usually 
have been formed the one a good while before the other. During 
that interval of time the first one will probably be able upon the 
average to throw one or more species before the second genus 
appears. It will thus get the start of the latter, and will con- 
tinually gain upon it. It follows from this that the larger the 
original genus now is, the greater, on the average, should be the 
gap between it and the second genus. As we have just seen, 
the third genus of a family will, upon the average, be separated 
from the second by less time than is the second from the first, and 
the time-separations will become less and less as we go downward 
to the smaller genera. We shall, therefore, expect the gaps in 
numbers of species also to lessen. 

Turning to the facts, this is exactly what we do find. Out of 
all the families given in my Dictionary — about 240 with two or 
more genera — only eleven, mostly very small, show no difference 
between first and second genus. The two larger families are 
Bignoniaceae and Sapotaceae, where the four top genera are all 
given as having 100 species. But on the average of all the families, 
the first difference is ninetj-nine, while the second gap is only 
thirty-two, the third eleven, the fourth eleven, the fifth six. 

The result of this test case, therefore, is in favour of differentia- 
tion. In fact, one cannot, with progressive arithmetical links 
like these between the genera, consider natural selection or gradual 
adaptation as having had much to do with the evolution. 


If natural selection of gradual adaptation be the moving power 
of evolution, and the small genera and local species be the relics 
of what must be regarded as the failures, then one would certainly 
expect that these ought to be more numerous in proportion in the 
small and local families, which are also regarded as relics. If, on 
the other hand, differentiation has been the mechanism, one will 
expect that the larger a family grows, the more rapid will be its 
proportionate production of small genera, for each genus, whether 
small or large, may be able to throw new ones, so that the small 
genera will be increasing (in number, not in size) more rapidly 
than the large, the family following the hollow curve. . pV A m 

WED .J\5^ ll J^ / 

98 TEST CASES [ch. x 

If we test these suppositions upon the facts, we soon find that 
the large and "successful" families have many more "relics" in 
them than have the small and "unsuccessful". In the Compo- 
sitae, the largest of all, the monotypic or one-specied genera form 
37-8 per cent of the total, while in the 151 small families containing 
not more than ten genera each they are only 29 per cent (figures 
twenty years old). The families with eleven to fifty genera have 
33 per cent of monotypes, those with fifty-one to one hundred 
have 36 per cent and those above have 39 per cent, a result which 
agrees well with the theory of differentiation, but not with that 
of natural selection. Even with the ditypic genera, their per- 
centage in families up to 200 is 12-25, and 12-75 above. 

If the small genera of one or two species are to be looked upon 
as relics of former floras, why are they so numerous? About 
38 per cent of all genera are monotypic, and over 12 per cent 
ditypic, so that these groups alone make up half the total number. 
Over 80 per cent of all genera have ten or fewer species. The hollow 
curve, as we have seen, goes so smoothly and uniformly that 
there is no possibility of drawing a line between successes and 
failures. The only explanation of these curves upon the theory of 
natural selection would seem to be that selection, as indeed one 
might expect from its name, is continually picking out fewer and 
fewer, so that its effect will be ultimately shown (when the relics 
have died completely out) in a vast di7ninutio7i of the numbers of 
species and genera. In other words, it is on its way to pick out a 
few "super-plants" from among a mass of inferiors. But if so, 
why did nature begin with so many? Their evolution cannot be 
explained by natural selection. The whole attempt to explain 
things upon this theory leads to so many absurdities that it 
becomes untenable. The simplest explanation is evidently that 
by using the theory of gradual adaptation in structural characters 
one is trying to work backwards. 

Every formation of a genus of two species (perhaps one may 
be enough) increases the number of genera that may be looked 
upon as capable of giving new genera of one, and as the larger 
genera also may be looked upon as similarly capable, the rate of 
production of monospecific genera will increase with the 
size of the family. As already explained, the ones, as newcomers, 
will be particularly slow at first in establishing themselves, so 
that there will always be a time lag between them and the twos. 

This test also fully favours the theory of differentiation. 



Many years ago it was shown that this curve, which is described 
in Age and Area, p. 195, and in Chap, iv above, is a universal 
feature of distribution in plants and in animals, both in regard to 
the areas occupied, and to the sizes of the genera in families by 
number of species contained. When plotted logarithmically, in 
the latter case, they give close approximations to straight lines, 
showing that they have the same mathematical form, and must 
be due to the operation of the same law. The production of such 
curves seems to the writer to place an almost insuperable ob- 
stacle in the path of those who would explain evolution and 
distribution in terms of gradual adaptation by means of natural 
selection. Yule has shown (75) that the curve would result from 
the continual doubling of the species and genera concerned, 
when one supposes the parent to survive as well as the offspring, 
as is the case according to the theory of differentiation. The curve 
then becomes a normal and necessary feature of the evolution 
that is going on, whereas under the theory of natural selection it 
is totally inexplicable. Opponents have tried to belittle it by 
showing that one can get similar curves from the names in the 
telephone book, and such like conglomerations of inanimate 
things. I have lately shown that the distribution of family 
surnames of farmers in Canton Vaud (69) is just like the distribu- 
tion of species, and therefore must follow the same laws, as it 
gives the same curve. Natural selection could not determine it, 
therefore it cannot be the determinant in the general distribution 
of plants. 

Nothing but a uniform pressure would ensure that results 
could be expressed in hollow curves. Family by family, and 
genus by genus, whether in numbers or in areas, all alike obey 
the same law. Natural selection could not produce results like 
this, and the only cause yet suggested is age, which represents 
the resultant of all the forces acting. If they produce an average 
result of <r in a long time 1, they will produce 2x in time 2. Age 
thus forms a measure of distribution, but one cannot compare 
unrelated forms, and must always work in tens of allied species, 
to average out the differences that there may be between them. 

It is clear that this test gives an unqualified verdict in favour 
of differentiation. 


100 TEST CASES [ch. x 


The hypothesis of Size and Space is more fully described in Age 
and Area, p. 113 ; it follows from that hypothesis. " On the whole, 
keeping to the same circle of affinity, the larger families and 
genera will be the older, and will therefore occupy the most 
space." If adaptational improvement ceases to be the prime (or 
even perhaps an important) factor in evolution, there is no special 
reason why one species should spread more rapidly, or over a 
greater area, than other species closely related to it. As an illustra- 
tion the case of distribution of species in Britain was taken, and it 
was shown that it increased with the size of the genus. 

"A good proof for the general correctness of Size and Space is 
that . . . the further out we go among the islands, the larger on the 
average do the genera become (in the number of species that they 
contain in the world). Whilst the world average for a genus is 
12-13 species, the non-endemic genera found in India contain on 
the average about 50 species in the world, in New Zealand 
about 75, and in the Hawaiian Islands about 100. 

"The smaller families usually occupy smaller areas than the 
larger, and the question arises whether they should be con- 
sidered of equal rank to the latter. Guppy has suggested a 
grouping of families into classes based upon these principles, for 
which he has suggested the title Rank and Range, and it is clear 
that in all future systematic work, the question of area must 
occupy some attention" (66). 

It is clear that the facts shown under Size and Space cannot 
be explained by aid of the hypothesis of natural selection or of 
gradual adaptation, and can at present only be easily explained 
by that of differentiation. 




To give details would simply be to repeat the paper of Mr G. 
Udny Yule and the author, in Nature, vol. cix, 9 February 1922, 
p. 177, and it will suffice to call attention to it. The general con- 
clusion was that: "Inasmuch as all families, both of plants and 
animals, show the same type of curve, whether graphic or loga- 
rithmic, it would appear that in general the manner in which 
evolution has unfolded itself has been relatively little affected by 
the various vital and other factors, these only causing deviations 
this way and that from the dominant plan." It follows that 
evolution must have been by mutation, and that this must, at 
times anyway, have been large, as demanded by the theory of 

CH. x] A. NUMERICAL 101 


We have seen (p. 96) that, in general, there is one genus in 
each family which on the average has at the present time nearly 
a hundred species more than the second genus ; the difference is 
only on the average thirty-two between the latter and the third 
genus, and so on. Only when one comes down into the smaller 
genera does coincidence in number happen at all seriously, and 
it happens more and more the nearer one comes to the bottom 
of the list, so that at last, if of any size, the family ends with a 
streamer of monotypic genera, or genera of one species each. This 
hollow curve, which is always formed, is what is to be expected 
upon the theory of differentiation, and natural selection is 
helpless to explain it. 

The hollow curve is due to the continual doubling of each genus 
in turn by the throwing of a new genus so that, as time goes on, 
the total number of genera undergoes an increase, which is con- 
tinually more and more rapid, as the numbers grow. And as time 
goes on, the genera already formed are supposed to increase their 
number of species in the same way. We have supposed, as the 
simplest solution of the problem for the meanwhile, that each 
genus will on the average throw a new genus rather than a new 
species once in every so many throws. In the counting that is 
being used for this particular paragraph, ^ the total number of 
families with more than one genus is 235. Taking the number of 
species in each genus of a family, and arranging the genera in 
descending order, the total number of species has been counted 
for each family, and halved, and a dividing line drawn immediately 
to the right of the genera required to make up the full half. This 
of course means that the genera on the left may contain the 
exact half (this is rare) or slightly or even considerably more ; but 
the numbers on the right-hand side of the line never exceed, and 
very rarely equal, those on the left. For example, three families 
are given : 

Aristolochiaceae 300 

Basellaceae 14 

Elatinaceae 19 

60 10 8 1 
3 111 


All of these have the dividing line after the first genus, and this 
proves to be the rule when the family is small, but not when it is 
large. Out of the 235 families, no fewer than ninety-eight, or 
41-7 per cent, have the dividing line after the first genus, as shown 

1 The numbers are continually being revised for my Dictionary, 

102 TEST CASES [ch. x 

above. Fifty of them have two, three, or four genera, the actual 
figures for the whole number being 22/2 (twenty-two of two 
genera), 21/3, 7/4, 9/5, 8/6, 6/7, 2/8, 5/9, 2/10, 2/11, 1/12, 1/13, 
2/15, 2/17, 1/19, 2/21, and one each of 24, 26, 28, 78 (Moraceae) 
and ninety-nine genera (Solanaceae). Arranging these ninety- 
eight families in order of size of the largest genus in each, one 
finds that though the average size of the families in each group of 
ten goes down with the average size of the largest genus, there 
are nevertheless, in the first ten, four families with less than ten 
genera each, but each headed by a very large genus {Begonia, 
Oxalis, Piper, Impatiens). 

The next lot of families is composed of those where the dividing 
line comes after the second genus, as in Primulaceae: 250, 120, 90, 
and so on to ten ones, total 651. While the average size of the 
ninety-eight families with dividing line after the first genus was 
7-9 genera with 201 species, the average size of those with the line 
after the second genus is 14-9 genera with 249 species. Going on 
in the same way through the whole number, we get the following 
table : Average 






Dividing line after the 

First genus 
























Seventh to tenth 








Figures in italics break the regularity of the table of averages. 

The larger, on the average, that the family becomes, the more 
is the dividing line pushed to the right, until in the Compositae, 
the largest family of all, it only appears after the thirtieth genus. 

It is clear that there is some arithmetical reason behind all this, 
and the simplest explanation is that it is due to the continual 
increase of species in genera other than the original one, when 
the latter divides off new genera (which again divide) at average 
intervals. In any case, the facts do not agree with any hypothesis 
of gradual adaptation working from below upwards. 

These numerical tests, to which others might be added, are 
thus all in favour of differentiation rather than of natural 
selection or of gradual adaptation. 




iN AT URAL selection, being a conmion phenomenon of everyday 
experience, has exercised such a fascination that it has to a 
notable extent inhibited people from trying properly to think 
out how a principle, whose essence is competition with partial 
escapes into usually temporary success every now and then by 
improved adaptation, can produce the ordered arrangement, 
taxonomy, and morphological or structural uniformity with which 
we are familiar. Herschel the astronomer, in an early criticism of 
the Origin of Species, is said to have called it the "law of 
higgledy-piggledy", and when one tries to imagine what mor- 
phology would be, under its unrestricted operation, it is difficult 
to meet this criticism. Why should natural selection produce such 
comparative uniformity in morphological structure? Why should 
there be such morphological likeness between the members of 
whole families, tribes, genera, or even divisions like the Mono- 
cotyledons? Why should the morphology remain the same, and 
not improve in later evolutions? Why should the larger (older) 
families appear in almost every kind of ecological conditions, 
though the members of any one of these families show greater 
structural resemblance among themselves than do the plants of 
the association that inhabits any given spot? A grass is an un- 
mistakable grass, whether in the tropics or in the arctic zone, in 
a dry or in a wet climate, in a bog or on a moor. To say that this 
is the case because it is a grass, and must retain the morphology 
of a grass, is no explanation, but only throws the task of explana- 
tion a little further back. Why and how were the grasses, or the 
crucifers, or the composites, evolved at all? Why is there nothing 
in common, in structural features, between say a grass and a 
crucifer growing in the same kind of conditions, and side by side, 
on a moor or in a pasture? One would expect natural selection, 
working by gradual adaptation to similar conditions, and deter- 
mining the structural features (as it must do if it is to be an 
explanation of evolution) to produce something of similarity. In 

104 TEST CASES [ch. xi 

actual fact, however, there is rarely much or any structural like- 
ness among the members of a given association of plants, unless 
they happen to belong to the extremes of the principal ecological 
divisions like xerophytes on the one side and hydrophytes on the 
other, or to special ecological groups like climbers or parasites, 
which do not, incidentally, grow in any special conditions, or in 
associations. Even in these cases, the ecological characters that 
mark them are rarely such as have great importance in classi- 

Were it not for the great structural differences that exist, we 
could not tell that evolution had gone on to so great and complex 
a degree. There might be herbs, shrubs, and trees, water-plants, 
epiphytes, climbers, plants of dry climates, bulbs, tubers, and so 
on, with other more or less adaptive forms, but there seems no 
a priori reason to suppose that we should find such things pro- 
duced by an adaptive evolution as the structural differences that 
mark whole families like the grasses or crucifers, and distinguish 
them from one another. As Went has said (50), we see the mor- 
phological differences, and assume that they must have some 
physiological explanation. But there is nothing to show that 
there is any physiological need for them. What connection can 
be shown between the great bulk of the structural features of 
plants and their physiological necessities? Man is adapted, region 
by region, to almost every kind of conditions that can be found 
upon the surface of the earth, yet he is all undoubtedly of one 
species, and does not show any great structural differences. And 
there are numerous similar cases with plants, though these are 
slower in movement, and have not covered so much ground. 
Some cover a very large area with no serious structural dif- 
ferences, like Hydrocotyle asiatica, Sanicula europea or Hippuris 
vulgaris, while in other places where the conditions are very much 
alike throughout, a genus may show a number of species. One 
can rarely infer from the external features of a plant, e.g. in a 
herbarium specimen, or even in a living one, from what kind of 
conditions it came. In the vast majority of cases, the most 
minute morphological description will convey nothing as to the 
habitat or the physiology, unless the plant happens to belong to 
one of the great ecological groups like water-plants or climbers. 
Can anyone read the characters in the most minutely descriptive 
flora, and locate the probable types of habitat of the plants? 

Taking genera with more than one species in the British flora, 
the first, Thalictrum, the meadow-rue, has three. T. alpimim, 


with a bi-ternate leaf, grows in alpine bogs, T. minus, with a 
tri-pinnate leaf, in chalky pastures, and T. flavum, with a bi- 
pinnate leaf, on river banks. In the next genus, Anemone, A. 
Pulsatilla, with a bi-pinnate leaf, grows in chalky places, and A. 
nemorosa, with a ternate leaf, in woods. Yet these two genera are 
closelv related, and surelv. if the structural forms of the leaves 
had anything to do with the conditions, the two with the bi- 
pinnate leaves would occupy places not very dissimilar. The usual 
reply of the selectionists to questions like this, that at some time 
there must have been such conditional differences that a dif- 
ference like that between these various types of leaf had a 
physiological significance, is simply an appeal to ignorance, for 
which there is not the slightest evidence. 

If one takes the matter the other way round, one gets a good 
argument against this contention of theirs. Why does one find 
pinnate leaves, to take just a few examples from the British flora, 
in Clematis, climbing in hedges, in Nasturtium in wet places, in 
Cardamine in meadows, Anthyllis in dry pastures, Vicia climbing 
in waste places, Sjnraea on downs, Potentilla by the roadside, 
Rosa in hedges, Myriophyllum in water, and so on; and why in 
Geum urbanum are the pinnate leaves only the lower, radical, 
leaves of the plant? The argument of the selectionists is clearly 
an admission of the point for which I am contending, that adapta- 
tion is mainly an internal, physiological, or functional process, 
without any necessary influence upon the outer, structural 
features of the plants concerned. 

The Englishman is successful enough in the conditions that 
obtain in England, but if taken directly to India, and asked to 
make good in the conditions to which the natives of that country 
are subject, he would fail, primarily on account of the very 
different climate. But he might succeed, if he were adapted by 
nature's method of extremely slow change, say in a quarter or 
half a million years. But by quick change he would be like the 
potato and the dahlia, which have not yet become acclimatised 
to Europe. Time is the needful thing in acclimatisation and 
adaptation, and nature has plenty of it available. But it is of 
course by no means unlikely that so great a change would be 
beyond the limits of the Englishman's possible adaptation; there 
are many cases in plants which seem to point to the existence of 
such a limit. From what we know of man, it is not to be expected 
that in the course of this adaptation the Englishman would suffer 
great morphological changes, though he might acquire a darker 

106 TEST CASES [ch. xi 

skin, as apparently have other northern tribes that migrated into 
India. The principal change that he would undergo would be a 
gradual physiological adaptation to warmer climates. 

Many, if not most or even all, of the characters of distinction 
that mark families, sub-families, and even smaller groups, are 
such that they can have no serious value upon the physiological 
side, which is the only one that matters from the point of view of 
natural selection or gradual adaptation. Only upon things with 
functional value or disadvantage can natural selection operate, 
and, as has frequently been pointed out by the writer and others, 
its important work seems to be the killing out, probably rapidly, 
of any variation definitely disadvantageous, though even here, as 
the struggle for life is mainly among seedlings, disadvantageous 
characters that only appear late in life may quite well survive. 
There is no doubt that natural selection would encourage the 
success of a new and improved form that had just arisen, but 
there is no evidence that it can continue to call up small variations 
or mutations always in the right direction, or that it can pass the 
rough and ready line of distinction that exists between species, 
that of mutual sterility, unless some mutation should happen 
that will do so. But work of this kind will not ensure progress 
such as seems to be the mark of evolution in general. Suppose a 
whole family to possess a septicidal capsule, or diplostemonous 
stamens. There is no evidence to show that there is any physio- 
logical value attaching to this possession, which in any case only 
appears in later life. One cannot imagine natural selection killing 
out a member of the family that had adopted (or was varying — 
if it could so vary — in the direction to adopt) a loculicidal capsule, 
or obdiplostemonous stamens, or was even going so far as a septi- 
fragal capsule. The family constancy of the capsule or the stamens 
must be due to inheritance from a common ancestor. But how, 
under selection, did the ancestor of one family obtain one kind of 
capsule or stamens, of another family another? With the recent 
revival of natural selection, there has been a recrudescence of the 
idea that characters that are of no physiological value tend to be 
very variable, but if so, why are family characters less variable 
than generic and specific, though they are admittedly of less 
physiological value? 

Plants, animals, and man alike tend to produce so many off- 
spring that, in a short time, but for various unfavourable condi- 
tions, there would not be room for them upon the surface of the 
earth. The illustration taken from the rapid multiplication of the 


green-fly is well known (42, p. 188) and even in the Podoste- 
maceae, annuals starting again every year, one plant might in 
four years cover about 100,000 square miles. The fiercest struggle 
for existence comes to a plant at birth, and any that is not suited 
to the conditions as they are at that moynent will be killed out by 
natural selection by reason of unsuitability, though of course mere 
chance will have a large influence in the matter. But this is an 
individual struggle, and we have no right therefore to assume that 
species struggle as units. Nothing can come into permanent 
existence without the permission of natural selection, but once 
the newcomer has become established in a few places reasonably 
far apart, the chance of its being completely killed out will 
steadily diminish, and in course of time may be reduced to 
vanishing point. Natural selection simply determines in each 
individual case whether or not a given plant shall be allowed to 
survive and reproduce. 

Very few indeed of the morphological features that distinguish 
one organism from another that is related to it have any physio- 
logical significance at all, especially in those features that 
separate the higher groups of plants from one another. Even the 
bulk of the generic and specific characters come into the same 
category. One cannot imagine any adaptational reason why 
Ranunculus should have over 300 species, and world-wide distri- 
bution, while its closest allies, like Myosurus or Oxygraphis, have 
few species, are comparatively localised, and differ largely in the 
fact that the wall of the fruit is not so hard. Still less can one 
imagine adaptational reasons taking part in the separation of the 
family Ranunculaceae into a group with achenes and another 
with follicles, or one with alternate leaves and one with opposite. 
Nor can one suggest adaptational reasons for the existence of 
200 species of Clematis, and still less for that of a couple of 
thousand Senecios or Astragali. If natural selection is to be held 
responsible for the vast dispersal of, and numbers of species in 
these genera, they must have some very great adaptational ad- 
vantage over their close allies. And the adaptation which was so 
successful must have been generic, for most of the species have 
but small areas. There is no species in these very large and wide- 
spread genera whose range covers that of the genus, though in 
smaller and less widely dispersed genera this is very commonly the 

It has frequently been shown, e.g. by de Vries (66, p. 224) and 
by J. T. Cunningham and others, that adaptation shows chiefly 

108 TEST CASES [ch. xi 

in generic and family groups, rather than in specific, so that any 
theory that tries to explain it on the basis of a commencement 
with the species, as does the Darwinian, must fail in its explana- 
tion. What adaptation there is, is rather handed down by 

The things that are usually considered to be gradual adapta- 
tions are steadily diminishing in number (cf. p. 116), and 
though it may come as a shock to some, one must add such 
things as climbers, parasites, saprophytes, lichens, fungi, herbs, 
trees and so on, for in most of these cases no intermediates are 
possible, or at any rate probable, and so much correlation (p. 129) 
is also required, which could not be effected by gradual adapta- 
tion. Trees, for example, are usually supposed to be older than 
herbs, but can any one imagine them being gradually selected 
down to herbs, especially when one remembers that both forms 
may not infrequently appear in the same genus, so that it is 
evidently, as in so many other cases, quite a simple matter to 
pass from one to the other? 

One might ask similar questions for the whole list of characters 
of family rank (Appendix I). Is there any adaptational difference 
between a superior and an inferior ovary, any between parietal 
and axile placentation, trimerous and pentamerous flowers, a 
dorsal raphe and a ventral, one cotyledon and two, or the various 
kinds of zygomorphism? Incidentally, median zygomorphism is 
looked upon as an adaptation to the visits of insects, but if so, 
why do transverse and oblique zygomorphism exist also? Why 
do the highly zygomorphic flowers of the Podostemaceae stand 
stiffly erect, whilst they are wind-pollinated also? 

Or, to go to generic characters, and taking a small family like 
Styracaceae, is there any adaptational difference between a 
flower with ten stamens and one with five? Between an ovary 
3-locular below and unilocular above, and an ovary 3-locular 
throughout? A flower with connate petals and one with free? Or, 
in the Caryophyllaceae, between a glabrous and a hairy stigma, 
a petal claw with and without wings, a capsule with teeth as 
many as carpels and one with teeth twice as many? We may even 
go on to species and still fail to find adaptational characters. It is 
impossible to read into the distinguishing characters any adapta- 
tional meaning which would be of any advantage in the struggle 
for existence, especially when we remember that the great 
struggle comes before the great bulk of these characters appear 
at all. It is an axiom in taxonomy that the less that any character 


has to do with the life of the plant, the more important is it from 
a taxonomic point of view. The higher one goes from species to 
family, the less connection have the characters with the life, and 
if one tries to think out how a mechanism like natural selection, 
depending upon improved adaptation, could thus have less and 
less to do with adaptation, the more it separated into larger 
groups the organisms with which it was concerned, one will 
speedily arrive at a deadlock. 

Two species usually differ in more than one character, even 
when closely related, and among the supporters of natural selec- 
tion it is, or has been, very often an implied assumption that a 
species A shall change fully to B before it goes on to become C. 
But one can see no reason whv this should be so : a variation in 
the direction of C would probably be just as useful in a plant that 
was only on the way to B. Natural selection can do nothing till 
the right variation is offered to it. Let us suppose that A is 
offered a variation in the direction of B and has started to adopt 
it, and that then a new variation is offered in the direction of C, 
obviously better, but in a different direction. What will happen 
then? Will it go on towards B and ignore the later offer, will it 
form C with a shade of B about it, or will it try to go back, and 
get rid of the traces of B, with the risk that it may not get another 
offer of C? There seems almost nothing for it but to demand that 
variations shall not interfere with one another, but that the one 
"in possession" shall be allowed to finish what it began, before 
another one is allowed to start. But this will greatly slow down 
the process of evolution, unless the variations are largely corre- 
lated. But why under natural selection should there be so much 
correlation? It is hard enough to find adaptational reasons for 
one variation, let alone half a dozen correlated ones. It would 
seem more probable and reasonable that in general the morpho- 
logical characters have no necessary physiological value, and are 
therefore not the result of any adaptational selection. If a new 
structural character appears that has an adaptational value, it is 
at once seized upon and perpetuated, unless in case of evil 
chance. But to regard structural characters as necessarily 
showing individual adaptational value — for example, that there 
is some necessary value in a pinnate rather than a palmate leaf, 
or vice versa — is to stretch the theory of gradual adaptation 
too far. 

It is a very remarkable thing that we do not find plants with 
a superposition of variations, one complete, the other incomplete. 

110 TEST CASES [ch. xi 

The only reply the selectionist can make is to say that the consti- 
tution of the plant does not allow of the mixture of characters, 
or, in other words, that structural considerations override 
adaptational. And as this reply comes in, in nearly all cases, it 
does not leave much room, if any, for gradual adaptation. 

The whole subject has suffered from the lack of proper thinking 
out. Everyone can see the struggle for existence going on before 
him at any moment. The individual who is in any way handi- 
capped, be it by some physical disability, by poor health, by low 
intelligence, by parental poverty (resulting in cheap schooling, 
underfeeding, etc.), or by other difficulties, is on the whole the 
one to be defeated. In the early days of the theories of Malthus 
and of Darwin (which was based upon Malthus) the tendency was 
to legislate (or rather not to legislate) in such a way as to leave 
the struggle for existence uncurbed, the idea being that in this 
way the best was brought to the top and the inferior left at the 
bottom, if not killed out. The theory of "nature red in tooth and 
claw" had, and still has, a great vogue. It was not realised that 
the winners in the struggle for existence owed their success only 
too often to some adventitious advantage which was not neces- 
sarily part of their own equipment. Money, for example, pro- 
viding the best food and education, was a great help. One has 
only to examine the trend of modern social legislation to see how 
we are drifting away from the old philosophy of the unrestricted 
struggle for existence. Everything possible is now being done to 
remove the handicaps that formerly were fatal to some of the 
best men, and to give to everyone the best possible chance, and 
there is reason to hope that in a few generations the results of this 
work will show a great social advance. 

Man is all of one species, and it is worthy of note that in his 
struggle for existence against members of other species, he has 
owed his success not to the slight morphological differences that 
distinguish his different varieties, but to internal adaptation of 
brain, etc., leading to greater skill in handling the difficulties 
that beset him. 


This test will be rendered more intelligible by aid of the figure (8), 
in which A represents a family of two genera only, B a family of 
intermediate size, and C a large family, both B and C being 
imagined a good deal larger than here shown. All are supposed 
accepted by the same systematists, to make their rank fairly 


equal. The diagram will serve for the growth of the families under 
differentiation, in which progress is supposed to work downwards 
from the original species and genus that began the family, A, B, 
or C, both species and genus of course being the same plant. As 
the family grows, it will form new species and genera, and all will 
on the average survive, so that the now existing family is in each 
case represented by all the dots under A, B, or C Whether the 
whole family, if seriously old, survive like this, will depend upon 

Level 1 

C. Cc. Cbb Cb 

CbChbCc C 

Fig. 8. Diagrammatic origin of small, medium and large families under 
differentiation, to show relative rank of genera in each, which goes more 
or less with the line 1, 2, 3 etc. upon which they happen to stand. 

what geological or other catastrophes it has met with, and whether 
any general change may occur in a genus, causing its death, or 
transforming it, or more probably one of its species, into another 
genus. The well-known fact that the smell was lost at the same 
time by all known examples of the common musk, once universal 
in cottage windows by reason of its sweet scent, shows that 
though a species may be represented by innumerable individuals, 
something may happen simultaneously in the internal make-up 
of all of them. And there is nothing to show that larger mutations 
than this are not possible. The way in which the successive fossil 
species of Stratiotes appear in different geological horizons, each 
specifically different from the preceding one, shows the kind of 

112 TEST CASES [ch. xi 

thing that may possibly happen, and again we have no reason 
why the change should not sometimes be generic as well as 
specific (3). 

Under the theory of natural selection, the existing plants will 
only be the lowest row in each family, for evolution, as we have 
already explained, is at present supposed to work by the forma- 
tion of slight varieties, which gradually increase to larger, to 
species, and so on, by the killing out of the less well adapted 
ancestors, while the ultimate survivors in the way of genera tend 
to be those that show the greater divergences. And the smaller 
the family, the greater are the divergences between its genera. 

To return to the diagram, under the supposition of evolution 
by natural selection, the various genera that occupy the bottom 
row in each family, whether in line 3, 4 or 5, will simply be genera, 
or generic stages in the evolution that is continually going on. 
Under this supposition, there is no reason why the genera in the 
lowest line, 3, of family A should in any particular way be any 
different from those in line 4, of family B, or these from those in 
line 5, of family C. Nor does natural selection offer any test by 
whose application we may gain any idea as to the relative degree 
of divergence that there may be between the genera of A, B, 
and C But upon the theory of differentiation or divergent muta- 
tion we shall expect that the divergence between the two genera in 
family A will he about equal to the first divergence in the families B 
and C, i.e. equal to the divergence between their tribes or subfamilies. 
At the same level in the diagram, in other words, there will be 
more or less equal divergences. It has long been known as an 
axiom in taxonomy that genera in a small family are much better 
separated than genera in a large one, and here is a simple expla- 
nation of this. As the family grows in size, new mutations will 
come in at more and more frequent intervals, but within, or close 
to, the original divergent mutation. In other words, all the 
family, sprung from the original genus and its first mutation, 
will show some at least of the characters shown by these first two 
genera, which by the hypothesis of divergent mutation will tend 
to be very divergent. The original family characters will show 
best in the largest genera, which will be the oldest in the families, 
and carry the most of the earliest characters. The genera sprung 
from later mutations will not have, so well marked, many of the 
characters of the earlier mutations. The generic characters will 
necessarily become on the whole closer and closer together as the 
mutations to which they are due are less and less far back in their 


ancestry. It would also seem as if there were a tendency in each 
family for mutation to become less pronounced as time goes on, 
so that the appearance of what we usually call family characters 
(list in Appendix I) becomes less frequent in proportion to the 
total of characters that appear. On the whole, there is more room 
for wider divergences the nearer one is to the starting-point of 
the family, i.e. to the original genus which gave rise to it, upon 
the theory of differentiation. Upon that of natural selection, it 
has always been a great difficulty to explain why the divergences 
became greater the higher one went in the key from species up- 
wards. Why should natural selection cause the disappearance of 
just those forms necessary to make the divergence increase? This 
is inexplicable by natural selection, working upwards from small 
differences, but simple to differentiation, working the other way. 

This being the expectation, we have only to look at Appen- 
dix III which gives the distinguishing characters of the two genera 
in those families that contain two only, to see that the facts 
agree with what was expected. The divergences are obviously of 
the same rank as those given in Appendix I as being "family" 
characters. If, on the other hand, one compare the generic 
characters in larger and larger families, one finds that as one goes 
up the scale, the genera, as one will expect under the theory of 
divergent mutation, get closer and closer together as new ones are 
"squeezed in" among the old. In a really big family, like the 
Umbelliferae, Compositae, or Gramineae, it is a familiar ex- 
perience that it is as difficult to make out the genus, as in a small 
family to make out the species. 

It is clear that we have not properly taken into consideration 
the relative rank of genera and other groups. In a very large 
family, where the genera have become closer and closer together 
by the continual appearance of new ones, the generic rank is 
evidently lower than it is in a normal small family. The ranks of 
all divisions in the classification, whether tribes, families, or 
genera, depend to a very great extent upon their relative sizes in 
their circles of relationship. This conception of relative rank has 
gone neglected during the reign of natural selection, to which a 
genus is simply a generic stage upon the upward road. 

If, on the other hand, the small family is to be regarded as a 
relic, as is done by the supporters of selection, it becomes neces- 
sary for them to explain why the divergences of the two or three 
genera that are left is so great, and equal to the divergence of the 
sub-families in a large family. Often one hears people say that 

WED 8 

114 TEST CASES [ch. xi 

the sharpness of definition in a small family is due to the fact 
that the family is small, with few genera. But this does not 
explain the fact that those genera have ahiiost without exception 
the rank of sub-families in a large family. 

The result of this test case is thus very strongly indeed in favour 
of the theory of differentiation as against that of natural selection 
with gradual adaptation. 


The fact, which seems to have been completely ignored, that 
structural characters are practically alwaj's shown both by 
animals and by plants in their perfect condition, is one which is 
simply incapable of explanation upon the ground of gradual 
acquirement, but simple if it be the result of a sudden mutation. 
The astonishing thing in the latter case would be to see an im- 
perfect acquisition. The perfect condition is best shown by the 
very widely divergent characters, like opposite or alternate leaves 
and many others that have no intermediates, in fact most of the 
characters shown in Appendix I. How can the divergence, under 
natural selection, have become not only larger but more perfectly 
marked? Supposing for the moment that an intermediate were 
possible between alternate and opposite leaves, and that there 
was such an adaptational urge that a plant began to progress in 
the direction of the latter. It is clear that once the leaves began 
to be nearly opposite, the urge would rapidly fall off, till at say 
95 per cent of perfection it would be quite small, and almost 
infinitesimal at 99 per cent. How comes it then that opposite 
leaves are exactly opposite? How comes it that a drupe or a berry, 
a capsule or a schizocarp, is always the same in structure (inci- 
dentally, why has evolution made no apparent attempt at im- 
proving them?), and always complete? In the same way, a 
disadvantageous character would be unlikely to be completely 
■got rid of. 

It is, I think, safe to say that natural selection could not dis- 
tinguish between 96 and 100 per cent of perfection, and that 
there must be some other principle that is responsible for the 
perfection that is always shown. By far the simplest explanation, 
and the only satisfying one at present, is that the perfection is 
due to a direct mutation. One can multiply examples to an 
almost unlimited extent. 


For that matter, how is it that all the leaves upon a plant 
match one another so closely as they do, or all the flowers? The 
only explanation that the supporters of natural selection can 
give is that morphological considerations are more important in 
evolution than is natural selection (cf. pp. 120, 121). But how did 
natural selection begin to develop different types of leaf, and 
to make them so constant in size and form, and to put different 
types upon closely allied species (cf. the Thalictrums on p. 104)? 
There is not the faintest reason to suppose that evolution worked 
by different rules at different stages in its history, but the selec- 
tionists seem to think that if by aid of assumptions and supple- 
mentary hypotheses they can produce some kind of explanation 
of the phenomena seen at the present day, the past can take care 
of itself. What we are contending for is that morphological and 
anatomical considerations are more important than natural selec- 
tion, and that the latter has not been, unless to some small extent 
or in some recondite way, responsible for the appearance of 
important structural characters. It acts upon what is given to it 
by the process of evolution, which goes on regardless of whether 
its products are acceptable or not. If they are killed out by 
natural selection, that is the end of that line, but others will 
appear. The simple and easy explanation of the phenomena of 
morphology is that they are due to mutations, which as a general 
rule probably produce a new form at one operation. To some 
extent at any rate, there is probably some definite factor in the 
parent, perhaps some arrangement or structure of the chromo- 
somes, that determines what will appear in the offspring (and 
here again perhaps only in certain conditions, as for example 
possibly under the influence of cosmic rays). But w^e are as yet 
too completely ignorant of the whole subject to be able to hazard 
any definite opinion. 

This test evidently gives very strong evidence in favour of the 
large mutations that are required by the theory of differentiation. 


One of the great difficulties that have always dogged the path of 
the supporter of natural selection as a cause of evolution, is to 
explain the beginnings of the various structural characters. This 
is a problem with which he has had little or no success. We have 
instanced many of the characters that divide species, genera, and 


« . 

116 TEST CASES [ch. xi 

families, and have shown that even when fully fledged it is im- 
possible to find any functional reason for their existence, and 
equally impossible to show why one should be preferred to the 
other, or to any (not commonly possible) intermediate, for any 
adaptational reason whatever. The adaptation to their surround- 
ings that is possessed by all living beings is primarily an internal 
affair. Descending from ancestors not too far away in distance, 
they presumably in most cases possessed an adaptation that was 
not very difl'erent from that of their parents — at any rate those 
that did not possess it would soon be destroyed by natural selec- 
tion. The adaptation might cover a greater or slightly different 
range of temperature or moisture, etc., that would enable them to 
reach places unattainable by the parents, thus ensuring ultimately 
a different distribution. 

All evidence goes to show that adaptation is rarely shown 
in structural characters, and it will be of interest to draw up a 
short list of some of those things that were considered as adapta- 
tions in the writer's early days; hundreds more might be added: 

Phyllodes in Acacia 
Thorny roots in Acanthorhiza 
Reversed leaves in Alstroeyneria 
Adventitious embryos 
Self-burying fruit in Arachis 
Hooked bracts in Arctium 
Clasping hooks in Artabotrys 
Cauliflory in Artocarpus 
Pollinia in Asclepiadaceae 
Thorns in Astragalus 

and many more in genera beginning with A. 

Red seeds in Paeonia 

Gutta-percha in Palaquium 

Horizontal fruit wing in Paliurus 

Scaly fleshy fruit in Palms 

Distribution by animals of stem joints in Panicum 

Distribution of Papaver seeds by pores in capsule 

Protogynous flowers in Paris 

Neuter flowers in Parkia 

Extrafloral nectaries in Passiflora 

Biennial life in Pastinaca 

and many more in genera beginning with P. 

It only requires that one should quote such cases as these, 
which are not selected, but simply taken in alphabetical order 
from my Dictionary, to show how the idea of universal adaptation, 


at one time held by almost everyone, has passed away, though 
natural selection, which is looked upon as depending upon 
structural adaptation, survives. 

But the great difficulty which has always hindered the selec- 
tionist is to explain how natural selection got a grip upon the 
early stages of any of these characters. If they were produced in 
one operation, as differentiation demands, everything is simple, 
but in that case it is clear that natural selection can have little 
or nothing to do with their appearance. One must drop out 
natural selection as a guiding cause in evolution ; it could get no 
grip upon the evolution of these structural features by gradual 
adaptation, and it could have nothing to do with it if they ap- 
peared fully-fledged. This test is in full favour of differentiation 
and what would seem the most probable order of things is that 
evolution, strictly so-called — the appearance of continually new 
structural forms — had little or nothing to do with adaptation of 
those forms to the conditions bv which thev were surrounded. 
They would inherit from the parents a reasonable probability of 
not being too unsuitable to survive at all, and it would then be 
"up to" natural selection gradually to fit them in minute detail 
for some particular combination of the conditions of life that 
existed near to the spot where they began, or to destroy them if this 
could not be done. Natural selection, in other words, strenuous 
though its action may be, has apparently nothing to do with the 
evolution of plants, though it has everything to do with the way 
in which they finally become best suited to some detail of com- 
bination of the conditions by which they are surrounded. Evolu- 
tion and natural selection, in other words, may be represented as 
working more or less closely at right angles to one another, and 
the evolution goes on by large steps, as required by the theory of 

The theory of gradual formation of the structural features of 
plants seems to be left with little or no support, and a much 
simpler explanation of everything is provided by that of sudden 
appearance. People say that we have no evidence of such an 
occurrence, but we have no evidence of gradual acquirement, and 
a mere glance at the table of family characters in Appendix I will 
show that a great number of them are so divergent that they 
allow of no intermediate, and if one therefore cannot derive them 
by stages, they must have come in one step. And this is especially 
true when one finds that gradual adaptation will not do as a cause 
for change. 

118 TEST CASES [ch. xi 


Here is a familiar pair of contrasting characters, occurring in so 
many different places in the flowering plants that it is clear that 
they must be very easily acquired, while sometimes one of the 
two may be shown by a whole family, as are alternate leaves in 
the grasses. We have already shown (74) that many or most 
large families show, somewhere in their make up, exceptions to 
most of the characters that usually mark the family. Thus in 
Rubiaceae,^ a very large family, one can find alternate, whorled, 
anisophyllous, pinnate, and gland-dotted leaves, leafy, and intra- 
petiolar stipules, dioecious, zygomorphic, and solitary axillary 
flowers, different male and female inflorescences, male and female 
flowers so different that at one time they were regarded as 
separate genera, flowers united in pairs, male flower 4-5-merous 
with female 8-merous, calyx convolute, imbricate, opening 
irregularly, with calyculus, with one large sepal, 5-merous in 
male and 2-merous in female; corolla aestivation descending; 
stamens united, unequal, 8-12, two only with a 5-merous 
corolla; anthers opening by pores, or by valves, multilocular, 
heterostyled, with poflinia; ovary superior, united in pairs, 
1- 3-5- 4- 6-10- or oo-locular; stigma 10 -lobed; capsule both 
septi- and loculicidal or circumscissile, berry, schizocarp; endo- 
sperm none, ruminate; embryo with curved radicle, or with no 

This is a very extensive list of exceptions, but most large 
families show something of the same kind, whilst even in the 
small ones divergence, usually just as pronounced as the diver- 
gences just given, is the common phenomenon, usually showing 
in them between the first two genera, or in the division into 
species if there be only one genus. 

It is clear that if one were to combine in a group of plants a 
number of the "abnormal" characters that have just been given 
for the Rubiaceae, say alternate leaves with intrapetiolar 
stipules, dioecism, zygomorphic flowers in male and female 
inflorescences different from one another, the male 5-merous and 
the female 8-merous; calyx imbricate with one large sepal, 
corolla with descending aestivation, united, unequal stamens, 

1 Usual characters decussate entire leaves with interpetiolar stipules; 
regular flowers in cymes or heads, 5-4-merous ; K usually open ; C valvate or 
convolute ; A 4-5, epipetalous ; G (2), 2-loc., each with 1- co ovules, style 1 ; fruit 
various; usually endosperm. 


anthers opening by valves, ovary superior with oo locuU ; fruit a 
schizocarp; embryo with no endosperm, no cotyledons, and 
curved radicle, a family would be produced that no one at any 
rate would imagine to have any relationship whatever to the 
Rubiaceae, and yet half-a-dozen to a dozen mutations might 
produce it. 

Divergence such as that shown by alternate and opposite 
leaves, or any of the divergences shown in the list of "abnormal" 
characters of the Rubiaceae is a matter of extraordinary difficulty 
to explain by aid of the hypothesis of natural selection. 
Neither of the divergent characters has any functional value to 
the plant that anyone has ever been able to prove, or even to 
suggest; nor as a rule is there any possible intermediate, nor 
could it have any value or the reverse. Yet the divergences show 
in so many different places among the flowering plants that they 
must be very easily acquired; they are even found quite com- 
monly between one genus and the next, or between some species 
and the next. But for such differences to be quickly acquired by 
natural selection, there would have to be some very pronounced 
advantage to be gained by their acquisition, and that is just 
what no one has ever been able to indicate. There is nothing to 
show that either opposite or alternate leaves have any advantage 
the one over the other, whilst an intermediate would still have 
alternate leaves, with a particular phyllotaxy. A point which is 
usually lost sight of, but is of great importance, is the difficulty 
of passing by aid of natural selection from say 95 to 100 per cent 
of perfection, already dealt with in Test case no. x. 

This question of the relative value or disadvantage of a 
character is another thing that has been completely ignored 
during the long reign of natural selection. The great struggle for 
existence is among the seedlings, and a character that is of im- 
portance one way or the other to a seedling has a far greater 
relative value than for example a character of the flower or fruit 
which only appears in later life, when the plant is more esta- 
blished and has greater reserves of food and vitality. Leaves, for 
example, are much more important, individually and even collec- 
tively, when the plant is young. Even if a character were defi- 
nitely disadvantageous it might still survive if it only appeared 
when the plant was old, whilst a disadvantageous character of 
any kind would probably be fatal to a seedling. 

The only reasonable explanation of alternate and opposite 
leaves would seem to be to suppose that they are determined by 

120 TEST CASES [ch. xi 

single mutations. The supporters of natural selection can only 
explain the exact nature of the oppositeness in the one case, or of 
the phyllotaxy in the other, by supposing that anatomical neces- 
sities are more potent than selection. Differentiation is much the 
most simple explanation, when one sees the well and exactly 
marked divergences that show so well, not only in leaves, but 
throughout the whole list of the characters that mark the dif- 
ferences in relationship of plants, and show that evolution has 
gone on. 


One may work through the whole list of family, or even of generic 
characters, and find similar phenomena in all, inexplicable by 
the theory of natural selection or of gradual adaptation, though 
simply explained by differentiating mutation. Why in so many 
families and other groups should a great and important dif- 
ference be that one has one whorl of stamens, while the other has 
two, or more? This dropping (or addition) of whole whorls of 
stamens cannot easily be exjDlained upon adaptational grounds. 
Fewer stamens are usually regarded as a mark of progress in 
evolution. But why, for example, in a family mostly provided 
with ten, like the Caryophyllaceae, should the "advanced" 
members (which in actual fact look less advanced) only have five, 
with no indication, fossil or other, that they have ever had ten? 
Why does one find no trace of plants with nine, eight, seven, or 
six? If it be of any advantage to reduce the number of stamens, 
surely nine would be an improvement upon ten, and so on. Why 
should the whole whorl be got rid of with no trace of intermediate 
stages? The supporters of selection, when confronted with a 
morphological problem like this, are obliged to defend themselves 
by bringing in another supplementary hypothesis, this time a 
"tendency", supposed to exist in plants, to vary the number of 
the stamens by whole whorls at a time, which of course is more 
in keeping with the general morphology of the flower, though it 
is a very remarkable thing that this tendency is so widespread in 
flowering plants, there being extremely few cases, so far as the 
writer can remember at the moment, of intermediate stages in 
regular flowers. In other words, the supporters of selection admit 
that morphological facts weigh more in evolution than does selection, 
and they also admit that large mutations can take place. And 
whence did this tendency come, if it was not handed down from 


the first ancestor of the whole family? Many of the families that 
now exist go back unchanged through the fossil records to more 
and more ancient times, or rather some of the larger and more 
widely distributed ones (the older, by age and area) do. There is 
no record of any preliminary stages in the development of a 
family, so that to imagine its characters as having been handed 
down from a first (single) ancestral form requires no stretch of 
the imagination, though it is not quite in keeping with the views 
derived from Darwinism. And as such large changes as the loss 
(or gain) of whole whorls of stamens are admitted, there seems 
no reason left why it should not be admitted that the family 
ancestor can appear by a single mutation. 

One more example must suffice — the opening of the anther by 
slits, by valves, or by pores. Here again, one of these characters 
may be found in a whole family, in part of one, in a few genera, in 
one, or even in some species only in one genus. But where does 
natural selection get any leverage upon the character? In what 
way can it possibly matter to a mature plant which of the methods 
of anther dehiscence is employed, or to a young plant how its 
anthers are going to open at a later period? And how can the 
differences arise except by direct mutations? Gradual stages are 
almost inconceivable. The only adaptational value ever suggested 
is that the valve or pore might localise the pollen better upon a 
visiting insect, but unless the stigma is also arranged so as to 
touch the part bearing the pollen, there will be no gain, but rather 
loss. And this brings up the question of correlated characters, 
about which something must presently be said. 

It is a matter of very great difficulty to account for morpho- 
logical uniformity unless it arise by direct mutation, and unless 
it be handed down from above, as differentiation demands. How 
did the widely distributed tap root come into existence in so 
many flowering plants ? How did the pore of an anther come to be 
like that of a fruit? How did leaves appear? Why have such a 
vast number of them much the same dorsiventral anatomy? 
Why are so many exactly opposite? Why are they in definite 
phyllotaxies ? Why are some simple and some compound, why 
are they entire or toothed, palmate or pinnate, and so on? How 
could all the Cruciferae, and they only, get tetradynamous 
stamens, which have incidentally no adaptational value, and 
have these together with the other well-marked characters of 
this family? Once more it must be admitted that morphology, or 
what the selectionists call tendencies, can override natural 

122 TEST CASES [ch. xi 

selection, and that natural selection can do nothing to explain 
staminal morphology. The phenomena shown can only, at 
present, be explained by the supposition of sudden mutation, 
causing, for example, the loss (or gain) of five stamens, or the 
formation of a new method of dehiscence, etc. 


The berry, as seen in the gooseberry or grape, is a well-marked 
and distinct type of fruit, the only hard part being the seeds, 
though there is a skin upon the outside. In the drupe, as seen in 
the cherry or the plum, the innermost layer of the fruit wall is 
hard, and the seed (kernel) inside this is usually soft. 

There are berries in about a third of existing families, and as 
these contain more than half the total of genera, they are upon 
the large (old) side. But only a portion of their genera have 
berries. Berries occur all through the flowering plants, including, 
for example, the Araceae, Bromeliaceae, Rafflesiaceae, Annona- 
ceae, Vitaceae, Myrtaceae, Ericaceae, Solanaceae, and Cam- 

The fleshy fruits have always been a standby of the supporters 
of selection, who of course had to find adaptational reasons for 
phenomena, and supposed these fruits to be adaptations for dis- 
persal of the seed. But if the seed be carried far, it will likely be 
dropped into another association of plants, where the competi- 
tion will be equally severe, and the conditions probably different, 
so that it will be, if anything, at a disadvantage. One rarely 
finds another plant growing in an association to which it is 

The berry and the capsule go together very much in related 
groups, but the capsule is much commoner, though it shows no 
adaptational advantage; the seed may be shaken out in a wind, 
but that is all. Some berried families, like Annonaceae, are com- 
mon and widespread, but so are capsular families like the 
Caryophyllaceae. There is no evidence to prove any adaptational 
value in a berr}^ An instance which was sometimes brought up 
was the family Taccaceae, where Tacca, with a berry, is wide- 
spread through the tropics, and Schizocapsa, with a capsule, the 
only other genus, is confined to Siam and South China. But in 
Dioscoreaceae, one berried genus, Tamus, is confined to Europe 
and the Mediterranean, and has only two species; the other, 
Peter mannia, with one species, occurs in New South Wales 


(incidentally, therefore, the berry fruit must have been acquired 
independently of that of Tamus) ; while Dioscorea, with 600 species 
and a capsular fruit, is in all warm countries. Such cases are 
common in many different instances of various fruits. There is no 
evidence to prove that advantage is gained by the possession of a 
berry. In fact, as was pointed out in Age and Area, p. 21, nothing 
in the distribution of plants would lead any one to suppose that 
the " mechanisms for dispersal " have produced for the plants that 
possess them any wider dispersal than usual. Tithonia, with no 
pappus, and with mainly vegetative reproduction, spread as 
widely as, and not much more slowly than, the bird-carried 
Lantana in Cevlon, to which both were introductions. 

The berry may occur in the whole or part of a family, in a few 
genera, in one, or in part of one. Considering the wide taxonomic 
separation of many of the berry families, it is clear that it is very 
improbable that all derived it from the same ancestor, unless the 
character could remain dormant for immense periods of time and 
change. It would rather seem to be one that is easily acquired, 
perhaps through some kind of kaleidoscopic change in the assort- 
ment of genes. 

To explain why the berry is more common than the drupe, 
which is equally well adapted to transport by birds or animals, 
the selectionists have to bring up one of their many supple- 
mentary hypotheses, this time a "tendency" to vary rather in 
the direction of berry than of drupe, or again an admission that 
morphological facts weigh more in evolution than does selection. 
Presumablv there is a still greater tendencv to varv in the 
direction of the capsule, the least "efficient" fruit of the three. 
And whence did the tendencv come, unless it were handed down 
from a common ancestor in each group, for whole families like 
Epacridaceae show a tendency towards the drupe, while their 
close relatives Ericaceae show a tendency chiefly towards the 
berry, but sometimes towards the drupe? Rhamnaceae have a 
dry fruit or a drupe, their close relatives the Vitaceae a berry. In 
the genus Chironia (Gentianaceae), mainly African, a small 
group of species in South Africa and Madagascar have a berry, 
the rest capsules. Why are there no berries in most of the generic 
area? This geographical localisation of structural features is 
common ; e.g. in Styrax, the first genus to come to hand, most of 
the species have sixteen to twenty-four ovules, but there are 
some with three to five in Cuba and in Peru. It is a matter of 
great difficulty, if not impossibility, to explain such cases by 

124 TEST CASES [ch. xi 

means of selection, but quite simple by mutational differentia- 

In the Caryophyllaceae, all otherwise dry-fruited (usually 
capsules), Cucuhalus alone, with one species in Europe and Asia, 
has a berry. In Ranunculaceae, admittedly a very old and widely 
dispersed family, Actaea has a berry, while in Annonaceae all have 
berries but Anaxagorea. 

In Myrtaceae, half the family, the Leptospermoideae, have a 
dry fruit, the other half, the Myrtoideae, a berry. How did 
natural selection, working upon the ancestors, ensure that all 
those with the berry should be more closely related to each other 
than to those with the dry fruit? Again "tendencies" have to be 
called in, but the differentiation answer is simple; an early 
mutation split off a genus with a berry from one with a dry fruit, 
and the descendants have inherited one or the other. An excep- 
tion like Cucuhalus is explained by a later mutation which in- 
volved a change of the chief fruit character of the family. 

A great difficulty is to explain why the berry is always the 
same in its general structure, though it must have been picked 
out upon so many separate occasions. Why is it usually associated 
with the capsule, while the drupe is usually associated with the 
achene or the nut? In some families both may be found, but each 
keeps strictly to its own morphology, though under selection one 
would have expected more variety. How did capsules and other 
kinds of dry fruits that occur in close relatives all manage to 
change to berries of the same morphological construction? No 
intermediate forms occur, with few and slight exceptions. It is 
clear that the phenomena of berries are better explained by 


Here again are types of fruit found all through the classification 
of the flowering plants. Alismaceae have achenes, while their 
near relatives the Butomaceae have follicles. Half of the Ranun- 
culaceae have one, half the other. Two of the three groups of 
Spiraeoideae have one, one the other. How were all these groups 
produced by natural selection with gradual adaptation? The 
question has hardly been properly thought out. How did the one 
fruit obtain, by this method, a completely closed wall, the other 
(when ripe) a completely open one? The value of selection would 
become less and less marked as the fruit approached perfection 


in either of these respects. Yet both the follicle and the achene 
show perfection — the one in its complete closure, the other in 
opening from one extreme to the other of the wall, and only on 
one side. Why, again, did selection cause only one side of the 
follicle to open, and that exactly, while the pod opens with equal 
accuracy upon both sides? No ada^^tational difference between 
them can be shown to exist. 

Ovules, again, cannot be developed in stages, from nothing to a 
complete ovule, though the reverse process is possible, but 
usually leaves some rudiments, which are not found in an achene. 
Nor can one imagine any transition — direct or through some 
intermediate form — from a multi-ovulate dehiscent fruit to a 
one-ovulate indehiscent. Nothing but mutation, and that con- 
siderable, could effect such a change, and as there is no adapta- 
tional reason behind it that one can conceive, a single mutation is 
more probable than a series of mutations. And again the morpho- 
logical question comes up — why are all follicles structurally 
alike, and why were they produced in preference to pods or to 
achenes? In the author's opinion, nothing but a complete muta- 
tion of considerable size can have produced the difference, and 
nothing but inheritance from a common parent can have caused 
it to be shown by whole groups of species, genera, families, etc. 
In other words, differentiation is the most probable explanation, 
and natural selection in any direct form is out of the question. 

Other types of fruit lend themselves to similar explanations, 
in which adaptation has but little if any part. It is, when one 
comes to think about it, a matter of extraordinary difficulty to 
show that the different fruits have any real adaptational value. 
What is the value to a tree like a Dipterocarp, which grows in 
dense practically windless forest, and often in a forest of one 
species only (pure stand), of its characteristic winged fruit? How 
could it, under the circumstances, have been developed by 
natural selection? Under gradual variation, all the sepals would 
vary alike, so that it must have begun with a mutation. And 
why should this be small, and not complete? In any case the 
calyx does not appear till the tree is perhaps thirty years old, and 
can anyone pretend that the struggle for existence between trees 
of this age and size is so severe that natural selection can get a 
leverage upon so slight a difference as the fact that two or three 
of the sepals are slightly longer? If anything, as the elongation 
will use more material, the longer sepals are more likely to be 
disadvantageous. If one say that the winged fruit gives the 

126 TEST CASES [ch. xi 

advantage of dispersal to some little distance — an almost certain 
advantage if not pressed too far — how were the non-winged 
parents killed out, unless the winged offspring were also superior 
to them in some functional character that enabled them to kill 
out the parents upon ground which they already occupied, and 
where they had the great advantage given by the fact that they 
were already established there, and that transport of seeds in 
windless forest was a very difficult thing? 


Another troublesome problem for the selectionist is to explain 
how the method of selection gave rise to large genera. Upon what 
grounds of adaptation did Senecio come to have about 3000 
species, and other genera also have enormous numbers, com- 
bining with the numbers a vast distribution over the earth's 
surface? If they owe their wide dispersal ("success") to adapta- 
tion, that adaptation can only have been generic. There are no 
characters in the individual species that one can point to as 
adaptive, and how could an adaptive and generic feature be 
produced in a genus formed from below upwards by the dying 
out of intermediates between it and its near relatives? If one of 
the species that were going to form Senecio had a really fine 
adaptation, one would expect it to go ahead and rather form a 
genus of its owti than simply join the rest. The bulk of the species 
in these big genera are local in distribution, and it is far simpler 
to explain the whole matter by differentiation and by age, which 
simply says that on the average the wider-dispersed species are 
the older. 

Other remarks on "generic" adaptation will be found on 
pp. 18, 59. 



Even in the comparatively few cases where a plant shows some 
structural feature that may be looked upon as a definite physio- 
logical advantage, like the tentacles of the Droseraceae, natural 
selection is hard put to it to explain how they could be formed by 
gradual adaptation. How, for example, did it produce the mar- 
vellously sensitive tentacles of Drosera itself, when the first steps 


in their formation would be absolutely useless, and when their 
movement would be of no value until it was perfected? Why did 
it also evolve Drosophyllum, with no movement, and with two 
kinds of tentacles ? And how did it place the tentacles in straight 
rows, and make them all alike? Again the reply has to be that 
morphological considerations inherent in the plant override the 
effects of natural selection. And why so, when they must them- 
selves have been derived in the same way? Further, how did 
natural selection evolve, in the same small family, Aldrovanda 
and Dionaea, with leaves that close up like a book? One does not 
expect to find, in so small a family, such marked differences; it 
reminds one of the Podostemaceae. The differences are much more 
marked than in a whole large family like the Compositae or the 

There is almost no end to the inexplicable difficulties in 
structure that can be brought up for the selectionist to try to 
explain. Here, for example, are a few picked out in hastily 
running through the list of family distinctions given at the end of 
my Dictionary: 

The windows in the leaves of Aponogetonaceae. 
The complex inflorescence of Zostera. 
The three-ranked leaves in Cyperaceae. 
The spiral or disc-like flowers of Cyclanthus. 
The pitcher of leaves in many Bromeliaceae. 
The resupinated flowers of Orchidaceae. 
The Equisetum-like stems of Casuarina. 

The explosive stamens of Urticaceae, etc. 
The integumentless ovule of Opiliaceae. 
The tetradynamous stamens of Cruciferae. 
The pod of Leguminosae (why not a follicle?). 
The obdiplostemonous stamens of Oxalidaceae. 
The cyathium of Euphorbia. 
The explosive capsule of Impatiens. 
The stinging hairs of Loasaceae. 
The asymmetrical leaf of Begonia, etc. 
The one-sided flowers of Lecythidaceae. 
The vivipary of Rhizophora. 
The free-central placenta of Primulaceae. 
The corona of Asclepiadaceae. 
The scorpioid cyme of Boraginaceae. 
The didynamous stamens of Labiatae, etc. (why 
do they match in several different families?). 
The four nutlet fruit of Labiatae. 
The pappus of Compositae. 

128 TEST CASES [ch. xi 

Nothing but common descent will explain most of these, and, 
if so, the family must have been very ancient, and why are there 
no fossil traces of any family formation, which must have gone on 
for an immense period of time if they were made by the method of 
dropping intermediates involved in the explanation by natural 
selection? Not only so, but the bulk of the characters described 
in the list above, to which hundreds more might be added, are 
such that they must have arisen at one step; either no inter- 
mediates are possible or they would have been completely useless, 
and therefore incapable of being chosen by selection. 


If the small genera are to be regarded as failures and relics, it is 
somewhat remarkable the way in which they are closely grouped 
round the large ones, usually regarded as the successes. If one 
take the two largest genera in a family^ — the two which upon the 
theory of differentiation represent, upon the average, the result of 
the first throwing of a new genus by the original genus which was 
the first parent of the family — one commonly finds them marked 
by a large divergence. But this same divergence is shown 
(cf. p. 84) by the groups of "satellite" genera round them, and 
these include the bulk of those which are classed as relics. Their 
characters are the chief characters of Ra^iunculus, for example. 
Upon the theory that Ranunculus owes its success to some of its 
visible characters, we should expect these to be the characters. 
Why then are the satellite genera so "unsuccessful"? Very few 
small genera are known which are not classed in the sub-families 
which are usually marked each by a fairly important genus at the 
head. And why should this be, unless the satellites were derived 
from the large genera? If this happened in the earlier days of the 
big genera, it is somewhat remarkable that one so rarely finds any 
fossil traces of the little ones, and if in the later days, w^hy should 
the big genera throw off, at such a late period, genera that were 
only to be relics or failures? It seems much more probable that 
the small genera were thrown off at a late period in the life of the 
large ones, by some larger change than would give rise merely to 
new species, but a change that could not have been the result of 
the work of natural selection. The test favours differentiation 
much more than it favours natural selection. 

<^"-^i] B. MORPHOLOGICAL 129 


The difficulty of imagining that evolution worked in the direction 
Irom species towards genus is vastly increased when we come to 
deal with the correlations that exist in the characters of the 
various flowering plants. Though there is usually no conceivable 
adaptational reason behind them, the characters of whole families, 
for example, usually go together in groups, for whose connection 
we can see no reason at all, unless it be simplv that the common 
ancestor happened to possess this combination. In the grasses 
there go together alternate leaves, in two ranks, a split sheath, a 
ligule, jointed stems, a spikelet inflorescence with glumes and 
paleae, and so on. How did natural selection pick out all these 
characters to go together, even if by any stretch of the imagina- 
tion one could imagine it picking out a split sheath in a grass, 
and a closed one in the allied sedges, or in fact any of the other 
characters? They must have been derived from a common an- 
cestor, and if so, where did selection and adaptation come in? If 
all the structural characters of a family, those characters in fact 
that mark it out as a family, are hereditarv characters, there is 
comparatively little room left for any adaptive characters at all 
and once again it is clear that morphological characters override 
selection. Even if there be no specially adaptive characters in 
the grasses or the sedges, there must have been some disadvan- 
tageous ones in the plants that were suppressed in the struggle for 
existence which made the wide gap that now separates these two 
allied families. But is it conceivable that a series of intermediate 
forms with, for example, a sheath partiallv split should have been 
so inferior that they were killed out? Still more difficult is it to 
imagine intermediates which showed intermediate characters 
m all the characters of diff^erence, if one suppose for an instant 
that such a thing were possible; there can be no intermediates 
between 2-ranked and 3-ranked leaves, or between the two types 
of inflorescence, etc. Direct mutation must have occurred in 
many cases; and gradual adaptation is hardly conceivable, 
especially when so many characters have to go together, and each 
has to be brought to the point of perfection (cf. p. 114). 

The larger the family, the greater on the average is the variety 
of conditions that it occupies, as may be seen in the grasses. Yet 
natural selection is supposed to form a family by gradual adapta- 
tion, and it is therefore clear that, as indeed the^ geological record 
shows, families must have come verij early in evolution, and the 


130 TEST CASES [ch. xi 

great variety of conditions in which the large families now live 
must have been due to subsequent adaptation. But this leads to 
the somewhat surprising conclusion that adaptation must have 
been very strongly in evidence in early days, with a corresponding 
amount of destruction to separate the families, for which we have 
no evidence. 

Or why were one-fifth of the flowering plants picked out to 
have only one seed-leaf instead of two, to have the parts of the 
flower in threes instead of in fives, to have leaves with parallel 
veins instead of netted, and to have so different an internal 
anatomy, with no simple process of growth in thickness? And 
still more difficult is it to explain, on the theory of gradual 
selection, why all these characters should go together, when they 
have no adaptational meaning, either singly or in combination. 
One can conceive that the anatomy of the Monocotyledons was 
definitelv disadvantao^eous, which mav explain whv there are 
comparatively few trees among them; yet the palms seem 
successful enough, or the bamboos. But the important fact 
remains unexplained, and not to be explained upon the theory of 
gradual selection, that, as already pointed out, the Monocoty- 
ledons maintain their proportion of one in five in all important 
parts of the world. 

An interesting case of correlation incidentally showing the 
totally useless nature of many, or nearly all, of the generic and 
specific characters may be seen in the genus Pyrenacantha in 
Icacinaceae, which has a drupe with the inner side of the shell 
thorny; correlated with this are definite holes right through the 
endosperm to leave room for the spines. Here is a case that it 
would puzzle the selectionist to explain, and there are many more. 
And it is somewhat difficult to imagine intermediate stages. 

To try to explain these correlations in terms of gradual adapta- 
tion is a practical impossibility, and if they were formed at one 
step, how does adaptation come in? Take, for example, the case 
of climbing plants, already considered (p. 57). Or take parasites, 
which must also have been a later development than non- 
parasitic plants. Until the sucker has actually penetrated the 
host, the habit will be of no value, so how did it begin under the 
operations of natural selection with gradual adaptation? And 
incidentally, such parasites as the fungi live almost entirely 
within the host, where the conditions must be more or less the 
same for all, so how did they come to develop such numbers of 
species with definite structural diff'erences? How did the ordinary 


leaf come to develop stomata, intercellular spaces, palisade and 
spongy tissue, and the fine network of veins, and how did it 
develop these last in so many patterns of netting, parallelism, etc.? 

Correlation, if large, implies that most characters have no 
bearing upon natural selection, and do not interfere with the 
results gained by the first character. And as differences in one 
character only do not usually cause mutual sterility, one wonders 
how that comes to be so common a mark of specific difference. 

One must look with great suspicion upon such easy interpreta- 
tions of things as calling them direct adaptations. If they were 
formed as such, the work was too complicated for natural selec- 
tion. It is more probable that they were formed at one step, and 
not being harmful, were allowed by natural selection to survive. 





JL HESE cases might equally well go under morphology, for 
taxonomy or systematic relationship is founded upon that sub- 
ject. The separation is simply used to prevent the morphological 
chapter from growing too large. 

It is of interest to note how easily the axioms of taxonomy 
that are given by Darwin in the Origin of Species are explained 
by the theory of differentiation. The first one, for example, 

Wide-ranging, much diffused and common species vary most 

fits in admirablv with much that has been said above, and with 
what the writer hopes to bring out in another book. It should 
also be compared with Guppy's remarks about the wide-ranging 
species that so often accompany endemics, and with what is to be 
said about the wide-ranging species that so often do the same 
thing in India (p. 158). One may also refer to what will be said 
about contour maps (p. 149). 

The current view is that the large and widely distributed 
genera and species are the "successful" ones, and that they are 
breaking up into new species by the formation of what as yet are 
only small varieties. On the view taken by the adherents of 
Darwinism, the Linnean species of the taxonomist is an abstrac- 
tion, consisting of an agglomeration of smaller forms that really 
breed true, and that may be more or less well assembled into a 
Linnean species which can be reasonably well marked off from 
others that are closely related to it. But upon the theory of dif- 
ferentiation the case is turned the other way round. There is little 
or no doubt that many of the very local endemic species, which 
are often supposed to be relics, but which upon the theory of age 
and area are regarded as young beginners, are well and clearly 
marked Linnean species. Take, for example, the Coleus elongatus 
(p. 24), or the Indian local species described on p. 159. The whole 
species, in cases like the Coleus, is made up of so few individuals 
that it is impossible that there should be a great range of varia- 
tion, for mere lack of numbers. It is after the formation of the 



species, when it begins to move into a greater range of conditions 
and climates, that it begins to show a range of smaller forms, 
which to the writer represent later stages in the continually 
diminishing mutation that began with the formation of the 
family, the genus, and this particular species. It is to be noted 
also that the great range of form only shows as a rule in species of 
the larger (or older) genera. When it does occur in species of 
small genera, the genus usually has a wide range, showing that 
it is probabl}^ old in its own circle of affinity. 

It is verv difficult to see whv on the Darwinian scheme the 
only genera of a very small family ("relics ") should be separated 
by as large distinctions as those that separate the sub-genera of a 
large family (p. 112), and why those distinctions should be so 
often such as are incapable of having intermediates, like many of 
those given in Appendix I. And it is equally difficult to see why 
the species of a single genus making up a family by itself should 
be grouped by such wide divisions as are instanced upon p. 79, 
again distinctions that do not often admit of intermediates. 

From the differentiation standpoint, the puzzle presented by 
these little "Jordanian" species, such as were described in 
Draba, for example (22), and which no stretch of imagination can 
show to be the commencement of new species derived by gradual 
adaptation upon the Darwinian plan, becomes quite simple. They 
are simply the last wavelets of the great disturbance that was 
made when the parent of the Cruciferae was formed from some- 
thing else by a "large" mutation that gave it tetradynamous 
stamens and the rest of the outfit of the Cruciferae. 

The second axiom is 

2. Sjjecies of the larger genera in each country vary more frequently 
than the species of smaller genera. 

Here again the variation w^as put down to the "success" of the 
larger genera, which were going on to develop new species, but, 
as explained above, it is much simpler to put it down simply to 
the age of the genera and size or area of the species, the larger 
being older, and having had more time to develop smaller muta- 
tions than that which gave the ordinary species. 

3. Many of the sjjecies included within the larger genera resemble 
varieties in being very closely but unequally related to each other, 
and in having restricted ranges. 

This is exactly what shows in the hollow curves. In the large 
genera there is a great proportion of species of small area, far 

134 TEST CASES [ch. xii 

more than of medium or large (cf. p. 98). In places where there 
are many of them close together, as with the big genera Eugenia 
or Memecylon in Ceylon, they are all more or less closely related, 
though many of them are quite good Linnean species. Attention 
may also be drawn to the "Jordanian" species in big genera like 
Draba or Hieracium. 

4. The varying species are relatively most numerous in those 
classes, orders, and genera which are the simplest in structure. 

5. As with species, so with genera and families. . .upon the 
whole those are the best limited which consist of plants of complex 
floral structure. 

6. Those classes and families which are the least complex in 
organisation are the most widely distributed, that is to say that they 
contain a larger proportion of widely dispersed sjjecies. 

7. This tendency of the least complex species to be most widely 
diffused is most marked in Acotyledons (Cryptogams) and least so 
in Dicotyledons. 

8. The ynost widely distributed and commonest species are the 
least modified. 

All these latter axioms go together, and obviously fit exactly 
with what would be expected under the law of age and area, 
which makes the older (and therefore on the whole the simpler) 
forms to occupy more area than the younger and more complex. 
The fact that all these dicta are axiomatic does not say much for 
the supposed continual improvement in adaptation under the 
operations of natural selection, especially as this theory also tries 
to explain greater range by the same improved adaptation. The 
whole of the axioms are rather against the Darwinian theory of 
progress, and are in much better accord with that of differen- 



On the theory of natural selection, one can make no prediction 
whatever as to the position in the classification of a family of 
the largest genera in it. There seems no reason whatever in any- 
thing that we know about them which should show that they 
should be near together, or that they should be far apart. But 
upon the theories of diff'erentiation and age and area, the largest 
genera should on the whole be the most widely separated, in- 


asmuch as they will have inherited their characters from the 
point that is the farthest back that is possible — the earliest 
mutational divisions that took place in the family concerned. 

In deciding this point we must, of course, work with the keys 
with which the taxonomists have provided us, but the latter 
have, of course, taken the greatest possible pains to find the most 
widely different characters that mark the different groups. In 
their keys they usually begin with very divergent characters, 
inasmuch as they have learnt by experience that these mark the 
largest divisions in the great majority of cases, separating the 
genera first of all into tw^o large groups. These groups again are 
separated by the most different characters that can be found, but 
which do not mark the whole, but only a part of the first group. 
And so on, breaking up the family into allied groups within 
allied groups — the general principle of all classification. 

One will, therefore, expect that the first one, two, or at most 
perhaps three separations that are given in any ordinary good 
key will separate not only the chief sub-families or tribes, but 
also the largest genera, and one will expect these to be separated 
by such distinct and divergent characters that there will be little 
or no difficulty in picking them out from one another. When such 
difficulty occurs, it should be in genera that have become so large 
that their outlying species, which will have been liable to more 
change than the earlier and more "genus-like" ones, have in one 
or two cases reached almost to the overlapping point. We should 
expect, but have not had sufficient time to test the matter, that 
these difficult species would prove in general to be comparatively 
local, that is to say, on the whole, the youngest species in their 
genera, which will have gone through the greatest number of 
mutations since the first throwing of the genus. 

As a test of this case, we may take the family Ranunculaceae, 
which is already described from this point of view in the chapter 
upon Differentiation. The first division of the family in most keys 
throws the largest genera on both sides. Here, for example, 
Aconitu77i, Aquilegia and Delphinium have follicles, and Anemone, 
Clematis, Ranunculus and Thalictrum have achenes. But as the 
two actually largest genera are Clematis and Ranunculus, 
separated by the very divergent character of opposite or alter- 
nate leaves, it is possible that this was the very first mutation, 
and that Clematis mutated off no other genera with opposite 
leaves. Or yet again, we must always bear in mind the possi- 
bilities of such complex mutations as are indicated in Hayata's 

136 TEST CASES [ch. xii 

work (16). All that we are at present contending for is that 
species and genera were formed each at one mutation, and that 
the change went downwards to the species, not upwards from it, 
as required by natural selection (of course a genus cannot exist 
without one species. 

In the same chapter (ix) we have also described the sub-family 
Silenoideae of Caryophyllaceae, and shown that the first split in 
the key throws Silene with 400 species to one side, Dianthus with 
300 to the other. 

This phenomenon, which is so common that it must have a 
reason behind it, occurs in a great number of cases. Picking up a 
few copies of the Pflanzenreich as they come, the first is Maran- 
taceae, where Calathea and Maranta, the two largest genera, are 
separated by the first split. In Myrsinaceae, Ardisia goes one 
side and Rapanea the other. In Amarantaceae, Alternanthera 
goes one side, Ptilotus the other. In Cyperaceae Cyperus and 
Carexdo the same; in Eriocaulaceae£'Wocat//on and Paepala?7thus. 
In Hydrophyllaceae, Phacelia and Nama go one side, and Hy- 
drolea, with only nineteen species but very wide distribution, the 
other. In Monimiaceae (p. 33) Siparuna goes one side and 
Mollinedia the other. And so on indefinitely. 

It is thus clear that as the position of the largest genera, and 
their sharp distinction in the great majority of cases, agrees with 
what is required by the diff'erentiation theory, while that of 
natural selection can give no idea where they will be found 
in a family, the evidence of this test is in favour of the former. 
Inasmuch as the classification of animals is equally possible, with 
equally good results, when conducted upon the same lines as that 
of plants, and as it shows the same hollow curves, it would seem 
highly probable that the same general principles have guided the 
evolution that has gone on in them also. 


We may even carr}^ the supposition outlined in the last test a 
stage farther, and apply it to families, saying that the very large 
ones will be very widely separated. We are still so undecided 
about the proper classification of the larger groups of plants that 
it will not do to push this very far, but one may note that the 
three largest families of all, from the latest figures in my posses- 
sion, are Compositae (18,039 species), Leguminosae (12,754) and 


Orchidaceae (10,088). Here, incidentally, is a case for the provisos 
with which I hedged age and area, that one must never com- 
pare anything but close relatives as regards age. To say that the 
Compositae are older than the Leguminosae is obviously a state- 
ment with nothing to back it. But the fact is there, that one 
could not easily find greater divergence than is shown by these 
three families, which incidentally contain nine out of twenty-nine 
of the genera containing over 500 species each. If we go over the 
first ten families in point of size, we find the fourth, Rubiaceae, 
to have one of these genera, the fifth, Gramineae, one, the sixth, 
Euphorbiaceae, three, the seventh, Melastomaceae, two, the 
eighth, Labiatae, one genus, while there are none in the other 
two. But these eight families contain seventeen out of the 
twenty-nine of these big genera, and most of the rest are in large 
families, though there are a few small ones which contain very 
large genera, like Begoniaceae. 

The twenty-seven large families with over 1500 species are 
Acanthaceae, Apocynaceae, Araceae, Asclepiadaceae, Bora- 
ginaceae, Bromeliaceae, Caryophyllaceae, Compositae, Cruci- 
ferae, Cyperaceae, Ericaceae, Euphorbiaceae, Gesneraceae, 
Gramineae, Labiatae, Leguminosae, Liliaceae, Melastomaceae, 
Myrtaceae, Orchidaceae, Palmaceae, Rosaceae, Rubiaceae, 
Rutaceae, Scrophulariaceae, Solanaceae, Umbelliferae. It will 
be seen at once how wide a range they cover in the classification, 
in fact touching all important parts of it. 

The evidence of both these test cases is strongly in favour of 
divergent mutation, forming the whole family or genus at one 



In making keys to families or genera, by whose aid one may 
determine the relationships and position of the plants with which 
one is dealing, the taxonomist is concerned with providing the 
easiest and most certain method of so doing. And it is a very 
remarkable fact, that has hardly been sufficiently recognised, 
that it is usually possible, without any very great difficulty, to 
make a dichotomous key (sometimes trichotomous at certain 
points), beginning at the top with characters that will separate 
one sub-family from another, and working right down through 
tribe, genus, and species, to variety, in the same way. This fact, 
which upon the theory of differentiation must occur, does not 

138 TEST CASES [ch. xii 

agree very well with the theory of natural selection, nor with 
that of gradual adaptation. There is no doubt that as one proceeds 
up the scale from variety, the divergence of the characters be- 
comes greater and greater, and upon these latter theories it is a 
matter of extraordinary difficulty to explain why the destruction 
of the intermediate forms should proceed in such a way as to 
leave groups that present divergences that are more and more 
marked the higher that one goes in the scale, while at the same 
time they are quite simple divergences, such as ovary uni- or 
multi-locular, anther opening by slits or by pores, leaves opposite 
or alternate, and the rest. Nothing but differentiation can at 
present explain such phenomena* 


It is a very noteworthy thing, which the selectionists have found 
so difficult of explanation, that they have had to fly to their 
usual refuges, that plants that show great divergences from the 
characters usual in their families occur, not in the small families 
(relics or failures) but almost only in the large ("successful") 
ones. We have given an instance from the Rubiaceae on p. 118 
and the matter is discussed in detail in (74, p. 621). In the large 
families one would be inclined to expect constancy, for if it were 
settled by the early ancestors of Papaveraceae, for example, that 
a hypogynous flower was the best, why did Eschscholtzia adopt 
a perigynous one? Solanum, by far the largest genus in its family, 
opens its anthers by pores, while most of the rest open by slits. 
Is this the generic adaptation that caused Solanum to become so 
"successful"? One could go on bringing up cases like these, and 
there is no escape from the conclusion, so far as our present 
knowledge goes, that characters of all kinds, however important 
in classification, may be acquired by single genera at any stage, 
so that their acquisition is evidently easy, and must almost 
certainlv be due to direct mutation. Like all the other tests this 
speaks in favour of differentiation. 


A puzzling case, which the natural selection theory can in no way 
explain, except by the favourite suggestion of "tendencies", is 
the parallel variation that so often may be seen. A good instance 
is afforded by the related families of Eriocaulaceae, Centro- 


lepidaceae, and Restionaceae. Each family makes its first divi- 
sion (in some classifications) into Haplanthereae and Diplan- 
thereae, or groups with monothecous and with dithecous anthers, 
a well divergent and clearly marked division. In the Erio- 
caulaceae the Diplanthereae contain half the genera of the 
family, including Eriocaulon and PaejJalanthns, which are by far 
the largest genera, while the Haplanthereae include only very 
small genera, whose species make only about 2 J per cent of those 
in the other group. And whilst the Diplanthereae cover the 
warmer parts of the world, the Haplanthereae are found only in 
warm America. In the Centrolepidaceae and Restionaceae, on 
the other hand, the larger group is the Haplanthereae. In the 
former, they include five genera and thirty-five species, against 
one and two in the Diplanthereae ; and in each case the distri- 
bution is much more extensive. 

There is no conceivable reason why dithecous anthers should 
suit America better, and monothecous the Old World, and yet 
the former are more common in the one, the latter in the other. 
It is clear that we must be dealing here with a divergent muta- 
tion, and that one family began with dithecous anthers, the other 
two with monothecous, and that probably each one subsequently 
split off the other division. The Eriocaulaceae, for example, 
beginning dithecous, spread over the world, but split ofP the 
monothecous group in America. Perhaps the splitting off was too 
late for the plants to cross to the Old World in any case, or it may 
have been that as we have elsewhere explained the early growth 
and dispersal of the new forms was too slow for them to be in time 
to cross. 

Cases of the same kind, showing exact parallelism, are very 
numerous indeed. To take a few examples, the Marantaceae 
divide into a group with 3-locular ovary, and a group with 
1-locular, and each of these divides into a group with two lateral 
staminodes, and a group with one. In Amaryllidaceae both the 
groups Amaryllideae and Narcisseae divide into groups with 
many ovules and with few, whilst this is the first division in the 
related Haemodoraceae. In Araceae, most of the principal groups 
divide into groups with endosperm and without. In the Palma- 
ceae, several widely separated groups have fan leaves, others 
feathers. And so on, in hundreds of cases. 

This phenomenon has always been a great difficulty to explain 
upon the theory of selection, for it makes it obvious that none 
of these characters — for example, those of climbing plants, else- 

140 TEST CASES [ch. xii 

where described (p. 57) — can be difficult of acquisition. In 
many cases differences of this kind can be seen between closely 
related species. The only reasonable explanation is that their 
appearance has nothing directly to do with adaptation, and is the 
result of simple mutation, which is so very commonly divergent. 
In other words, this phenomenon, which is so very common 
throughout the vegetable kingdom, and which is not unknown in 
the animal, is an expression of the operations of differentiation, 
not of those of natural selection, while at the same time it 
suggests complications in evolution, perhaps like those suggested 
by Hayata (16). 


That the higher groups of organisms, for example the flowering 
plants, are more localised in distribution than the lower groups, 
such as the ferns, has long been an accepted axiom, and has often 
been put down, as for example by Darwin and by the author, 
largely to the greater antiquity of the lower groups. But if we 
carry this principle into greater detail, it is clear that if in any 
family or group of families some forms are more widely distri- 
buted than others, those forms should on the whole be the older 
— the principle for which the author contended in the hypothesis 
of age and area. But the explanation of geographical distribu- 
tion that is given by natural selection, or gradual structural 
adaptation, involves the assumption that the forms that have 
spread the most widely will be those that are the best adapted, 
though to what they are adapted is left vague. Upon this view of 
evolution, one cannot regard genera like Carex, Draba, Eryngium, 
Eugenia, Eujjhorbia or Senecio as being poorly adapted when 
compared with the vastly more numerous smaller and more 
localised genera. But when one asks why such families as Cepha- 
lotaceae, Hydnoraceae, Nepenthaceae, Orobanchaceae, or Sar- 
raceniaceae have not spread widely, with such "adaptations" 
as they show, one is told that their adaptation is too special to 
have allowed them to do so. But why should Nepenthes, for 
example, be well suited to the variety of conditions with which it 
meets in Malaya, Ceylon and Madagascar, and yet not capable of 
withstanding those of tropical Africa, America, Polynesia or 
Australia? The Sarraceniaceae, with not dissimilar adaptations, 
can do so, and do not occur in the Old World. It is not even as if 
there were only one species in each of the genera ; there are scores 


of Nepenthes^ for example, so that the adaptation which enabled 
the genus to spread must have been generic, perhaps principally 
the pitcher. But if so, why could not some species have been able 
to live in America, or some Sarracenias in Europe? No feature 
can be pointed out in the pitcher or any other character of 
Nepenthes, which should limit it to its present distribution. 
Sarracenia, as pointed out on p. 56, is naturalised in a bog near 
Montreux. Nothing but an explanation based upon age and 
area will answer the innumerable questions like this w^hich come 
up in a study of distribution. 

This feature, that the enormous distribution of large genera 
like Carex or Senecio can only be explained by generic adapta- 
tion, if one is to accept the "explanation" given by natural 
selection, is a very fatal objection to the theory. The six genera 
above mentioned average a thousand species each, and it is a 
very astonishing thing that the original adaptations should have 
been such that they remain in their progeny after all this degree 
of change. 

As in general we are not alwavs verv sure of what we mean 
when we say that one genus is more complex than another, and 
as opposite views are frequently expressed in any particular 
case, it is fortunate that in the Podostemaceae and Tristicha- 
ceae we have families where it is almost impossible to be in 
doubt, for the obvious change that has gone on is from a slight 
to a great dorsiventrality. The comparatively primitive forms 
are widely dispersed, the more modified are local. 

It is fortunate that we have this evidence, for usually it is not 
easy to draw conclusions from the morphology. It is often said, 
for example, that reduction in number of stamens and carpels is 
evidence of progress, yet we can find the widely dispersed species 
in some families showing the one thing, the narrowly dispersed 
in others. For example, with leaves alternate/opposite, the 
Erythroxylaceae go one way, the Caryocaraceae the other; with 
flow^ers regular/irregular, Aristolochiaceae and Commelinaceae 
go one way, Dichapetalaceae the other. With corolla valvate/con- 
volute, Quiinaceae go one way, Cistaceae the other, with stamens 
cX)/few we have Loasaceae and Papaveraceae/Quiinaceae and 
Velloziaceae. With carpels oo/few, Papaveraceae/Portulacaceae, 
and so on indefinitelv. 




X HIS group of test cases is placed last, as the author is at 
present writing a book upon geographical distribution, and many 
tests that could be given would require such long quotations 
from that work that they are not suitable to the present one. 

Geographical distribution, properly so called, unlike ecology, 
is so bound up with the question of the origin of the species with 
which it deals, that it must be based upon some theory of that 
origin, and this theory must be able to explain all or most of the 
well-known facts of distribution without serious difficulty. To 
take one case only, special creation could not explain the 
relationship of species in one country, say Britain, to those in 
another far removed, like New Zealand. It was succeeded by 
natural selection, which, however, did its great work rather in 
establishing evolution, and thus opening out a great field for 
research, than in explaining geographical distribution. Not only 
did it show that resemblances were mainly due to relationship, 
but it also seemed to show that wide dispersal, or successful 
spread, as it now began to be called, must be due to unusually 
good "adaptation". This latter, however, has never been proved. 
The struggle for existence was undoubtedly in full operation 
among individuals, but even there, chance had probably a much 
greater effect, for the great struggle was amongst the young, and 
better water supply, better light, better soil, earlier arrival or 
germination, etc., etc., would have greater effect than any slight 
advantage that the young plant could carry in itself. 

Natural selection had to explain geographical distribution, and 
there seemed no other way to explain it than by transferring the 
hypothesis from individual to species; but as yet we have no 
evidence in favour of this great assumption. We do not know that 
species or varieties can come into direct competition with one 
another as units in a war a Voutraiice, especially as in general 
they will occupy more or less different areas, and one would 
hardly expect that species B would follow its defeated rival A 
into all its habitats, and kill it out there. If this was the way in 


which one species won at the expense of another in the struggle 
for existence, one ought to find many cases of this internecine 
struggle going on in many places, but one does not. One only 
finds a struggle between individuals, in one place a member of 
species A being successful, in another a member of B. 

The supporters of selection say that the intermediates, which 
also came into the competition, have been killed out, and that the 
two survivors are now adapted to slightly different conditions. 
This is of course possible, but it is a very remarkable thing, 
when one thinks of all these processes going on gradually, as must 
be the case under the old theory, that one does not find inter- 
mediates in the fossil deposits. What are sometimes called inter- 
mediates are really a very different thing, usually plants with 
some of the characters of one, some of another, really a very good 
argument for differentiation. And further, why does one not 
find intermediates at the present date? Is the competition now 
finished? One would expect to find some cases in which it was 
still going on. We have already seen that in a great number of 
cases, especially in those high in the scheme of classification, inter- 
mediates between the characters are actually impossible, and 
how mutation, crossing the whole gap between the two at one 
operation, is the only probable explanation. It is no argument in 
favour of this supposition, that species can act as units, to say 
that masses of men of (to some extent) the same race, like the 
Fijians or the Hawaiians, can act together as units. Man has 
sufficient intelligence to be able to combine to some slight extent, 
though it is a somewhat ironical commentary upon that intelli- 
gence that his chief and most efficient combination is for the 
purpose of making war, whose results are more against natural 
selection than for it. 

The new and better adapted form was supposed to kill out the 
less well-adapted parent. But as they would usually meet only at 
the edges of their respective territories (p. 13), where they 
would tend to cross, and to lose their identity, it would require 
a vast amount of time for the new one to invade the territory of 
the unimproved parent, and to kill it out entirely. Almost cer- 
tainly examples of the old species would be left in many different 
spots, where they had been overlooked, a feature which in actual 
fact is very rarely seen. 

Incidentally, the new species would have to kill out all the 
hybrids at the meeting place of the new and the old, and if it 
had not crossed the "sterility line" it would continue to make 

144 TEST CASES [ch. xiii 

more hybrids, so that the only result of an incipient species 
trying to gain territory at the expense of its parent would be the 
continual formation of hybrids. Only when the sterility line had 
been crossed would the new species really be able to conquer the 
old, and to supplant it. But it is very hard indeed to see how this 
line can be crossed in any case without a large mutation that will 
create a new species at one step; one cannot easily imagine a 
species gradually crossing the line of sterility, nor even a series of 
small mutations doing it. 

There is evidence to show that on the whole the parent will 
continue to gain in dispersal upon the offspring (66, p. 34), and 
if this be so, it could not be altogether killed out, unless the 
assumption that the offspring, by becoming better adapted to 
place A, became thereby better adapted to B, the home of the 
parent, were correct. There is little or no evidence that a species, 
and still less a variety, fights as a whole, and an organisation that 
is based upon such a contention, as so much political organisation 
is at present based (the operation of the dead hand, so well 
described in Woolf's Aftei' the Deluge, chap, i), has no strong 
scientific backing. 

To carry out evolution by natural selection involves a vast 
amount of destruction, for which we have no evidence in fossil 
botany or elsewhere, whilst such destruction is not involved in 
the theory of differentiation. To try to explain the phenomena of 
geographical distribution upon the supposition that one species 
has conquered and destroyed another is to build upon a somewhat 
insecure foundation. It has hitherto been assumed that a widelv 
dispersed species owes its dispersal to the fact of its superior 
adaptation. But to ivhat is it adapted, and how in country A did 
it become adapted to the conditions of country B ? If its range be 
large, it must come into greater variety of conditions than if its 
range be small, and that must mean that as it moved about it 
became functionally adapted to all these conditions in turn, but 
that is no proof that in becoming adapted to B it retained the 
adaptation to A. But in any case much time must be allowed, 
i.e. that wide-ranging species are usually old, a supposition that 
agrees with age and area. The more local species, which do not 
occur in such variety of conditions, are the younger. It would, 
therefore, form a much more probable explanation to say that 
the widely dispersed species were the old ones, dispersed before 
the land was broken up into its present divisions, and before the 
climates showed so much differentiation as they do at the present 


time. These old forms, being simpler, would show less adaptation 
to any particular conditions, but would probably show greater 
adaptability. This conception agrees much better with the facts, 
which go to show, as was pointed out by Darwin, that the organi- 
sation of the widely dispersed species is definitely simple rather 
than complex, when allies only are considered, as must always 
be the case in general comparisons with regard to age (cf. p. 29) or 

All the facts that are known go to show that in the majority of 
cases an individual plant arises in a place at no great distance 
from that where its parent is to be found. If it survive, and grow 
to the reproductive stage, one may conclude not only that chance 
has favoured it, but also that it has probably passed through the 
sieve of natural selection, and may be said to be more or less 
suited to that locality. If the seed, however, be carried to a 
greater distance than usual, say to more than 250 or 500 metres, 
whether it prove so suited to its new locality as to survive and 
reproduce there will depend upon a number of things. It may 
find a good deal of difference in the soil, though not perhaps in 
the climate, and if it has been carried beyond the range of the 
particular association of plants in which it has been growing, 
there may be considerable biological differences, which again may 
be accompanied by soil changes and the like. It will then be a 
matter of chance whether it prove suited to the new locality — to 
talk of adaptation in a seed only newly arrived, though it may 
prove suited to the place, would be going too far. If it survive to 
the reproductive stage, it will probably have begun by that time 
to adapt itself to its new surroundings. In each successive genera- 
tion this adaptation will continue, until, after a time which is 
probably different in each case, it has again become fully adapted 
to local conditions. This process may continue until, after a very 
long period, the species may cover, as does Hydrocotyle asiatica 
(p. 58), a very large area of the surface of the globe. If we 
abandon the notion that adaptation is shown by the structural 
characters of plants, but that it is much more the physiological or 
functional adaptation that must go on in any plant that moves 
about and comes continually into new conditions, the supposi- 
tion that we have just given explains, with the aid of age and 
area, why species are arranged over the world in "wheels within 
wheels", why the largest numbers are found upon the smallest 
areas, and those that occupy larger areas decrease in a "hollow 



146 TEST CASES [ch. xiii 

If the conditions begin to change in any place, the new ones 
may encourage some plants, and discourage others, so that 
natural selection may in time effect a change of the local flora, 
some plants coming in from other near-by regions where condi- 
tions are more or less like those which now obtain in the locality 
under consideration, and some of the local ones perhaps dying 
out in that region. Possibty, even, under the stimulus of changed 
conditions, new endemics may appear. But while plants that are 
really very local may be completely killed out by a serious change 
of climate or other conditions, it is very unlikely that this will 
happen with plants that are already widely dispersed into a 
considerable variety of conditions. To imagine that a species that 
has become well adapted to certain conditions that occur in one 
country has become thereby adapted to those that may occur in 
some country widely separated from the first, is to press the idea 
of adaptation altogether beyond possibility. 


There is no need to add much to the description already given 
in chap. iii. One of its striking features is the proof that it gives 
that the distribution of a plant within a country, such as Ceylon 
or New Zealand, goes on the average with its total distribution 
outside that country. When one considers the differences in con- 
ditions that must exist, this goes to show that natural selection, 
in the sense of gradual structural adaptation, can have had little 
or nothing to do with the distribution. What kind of an "adapta- 
tion" can a species have acquired that enables it to go so far 
afield, into so great a variety of conditions? And still more diffi- 
cult is it to explain why the species that are endemic in any given 
country are usually closely related to these species of large and 
widely ranging genera. 

In Ceylon, for example, and the same can be said of other 
places, the species that are most widely dispersed locally, on the 
average, are those that range beyond the South Indian peninsula, 
i.e. beyond a line drawn from Bombay to Calcutta. The next most 
widely dispersed occur in Ceylon and in the peninsula only, 
while the least dispersed are the local or endemic species that do 
not occur outside Ceylon. All, of course, as pointed out in Age 
and Area, must be taken in averages, as an endemic in an old 
genus (in Ceylon) might be much older, and occupy more ground, 
than a newly arrived "wide", even if the latter also ranged to 


tropical Africa or America. But on averages there are very great 
differences between the species of the three groups, and the 
statement above made as to relative distribution is fully borne 
out in all cases that have been investigated. Between the widely 
distributed species and the local endemics in New Zealand, there 
is a great difference in range (average length for wides 742 miles, 
for endemics 414). 

On the theory of natural selection, it is quite impossible to 
make any prediction about what is likely to be found in studying 
the distribution of plants in such a place as Ceylon. The sup- 
porters of that theory tried to answer the author's attack by 
calling in two supplementary hypotheses, which as already 
shown (p. 24) are mutually contradictory. The Ceylon local 
species were supposed in the first to be local adaptations to the 
Ceylon conditions. But this did not get over the difficulty of the 
intermediate distribution of the species that also occurred in 
South India. Were they suited to the conditions that occurred in 
both countries, and if so what were those conditions, and how did 
natural selection adapt plants in such a way that some Ceylon 
things were confined to Ceylon, some reached as far as say 
Cochin in South India, while some got as far as Goa and some to 
Bombay? This overlapping of areas, which shows in all parts of 
the world, is a fatal objection to the theory of local adaptation as 
a general rule for the explanation of endemics, without something 
else to explain the varying distribution that they show. But in 
any case, it was a very remarkable thing that if they were really 
local adaptations to local conditions, they should be the rarest 
plants in those very conditions. Their general distribution was 
simply a reproduction on a smaller scale of the kind of distribu- 
tion that might be seen in any big genus or family, or in the 
flora of any big country — all gave the same "hollow" curves. 
There was nothing peculiar about local endemism to distinguish 
it from any other type of distribution. 

The rival supplementary hypothesis, which contradicts the 
first, and is the popular explanation at the present time, is that 
the endemics of a country are the relics of a previous vegetation. 
The tenacity with which this opinion is held, in spite of all 
evidence to the contrary, is really noteworthy, though a weakening 
is to be seen in the tendency to expand the idea of a relic. Such 
things as Ceanothus in North America may perhaps be brought 
into this category, though the genus has about forty species, 
which puts it very definitely into the large genera, but it does. 


148 TEST CASES [ch. xiii 

however, seem to belong to the vegetation that was largely 
destroyed there by the ice. But things like Artocarpus, with 
over sixty species, common in warm Asia, are now being called 
relics, because they have fossils in places not now occupied by 
them. But if these plants are to be counted relics, one might as 
well say that all widely distributed things, but probably not the 
local or endemic, are relics, for there are few widely distributed 
things that have not the possibility of fossils somewhere, for 
example the whole British flora that anywhere reaches the coast. 
There are rarely any fossils of the small and local genera that are 
usually called relics. 

But the hypothesis of relicdom is no better than that of local 
adaptation in explaining the intermediate position of the 
Ceylon-South Indian things in the distribution. Are they half 
relics? No hypothesis other than that which we have termed age 
and area can explain the "hollow curve" into which all kinds of 
distribution fit. No theory involving natural selection or gradual 
adaptation can explain why 38 per cent of the genera of the 
world have only one species, 13 per cent two, and only 7 per cent 
three, and why the proportions are very much the same wherever 
one may go. There is no escape from these facts, and to say that 
they are accidental is simply to admit that the distribution of 
plants is largely accidental, and to ignore the rule under which 
they have probably come into being, the simple doubling of 
every species at intervals as time has gone on (cf. Yule, 75). The 
author has lately shown that the distribution of family sur- 
names in the mountainous regions of Switzerland follows exactly 
the same rules as does the distribution of plants. No invocation 
of natural selection can explain why Rochat, which is a common 
name in its place of origin (the valley of Joux), should have spread 
more widely in the canton of Vaud than Capt, which is less 
common, or why the surnames should be arranged in "wheels 
within wheels" just like the species of the Ceylon or other floras. 
Nor can one invoke gradual adaptation to explain why in the far 
north-east of its range, Rochat is replaced by Rojard, which is 
much more easily explained by the general illiteracy of former 
days, and largely matches the way in which plant varieties occur. 
It wfll perhaps be well to quote part of the original note, by kind 
permission of the Linnean Society (and cf. fig. 6, p. 40). 


Surname-distribution of farmers 
in Canton Vaud {Switzerland) 

As a sequel to Guppy's study of surname-distribution of 
farmers (who move about less than usual) in Britain, which 
showed a good "hollow curve" by counties, the author has 
studied Canton Vaud, which is about as large as Gloucestershire, 
but much broken up into more or less isolated valleys by moun- 
tains larger and smaller. Its nineteen "districts" average 64 
square miles each, and they show as good a curve as, or even 
better than, that of the English counties. A. very great number 
of the villages, especially in the more rugged districts, contain 
endemic names found nowhere else in the Canton. Not infre- 
quently these occur on more than one farm, and then they 
usually show a curve just like that of plants, with the greatest 
number upon the smallest area (here one farm). The spread of 
a name may be due to various causes that can hardly be regarded 
as other than chance, as for example the chance that a farm may 
fall into the possession of a woman of family X. If she marry 
a man of family A, that family will rise in status by one farm, 
and X may even be extinguished. The same process happens 
with plants, and the plant (or the surname) that increases its 
numbers increases its chance of spreading. The bulk of the 
villages in the Canton have one or more names exceeding the 
rest in number, and in general these names show greater dis- 
persal in the Canton (just as the commoner plants in Ceylon, 
for example, show greater dispersal outside the island). Spread 
is alike in the two cases, so that it becomes very difficult to call 
in adaptation or natural selection as the chief causal agent in 
distribution. Rochat, for example, is the commonest name in the 
valley of Joux, and has spread the most widely of the Joux names 
in the Canton. But there is no adaptation, nor any handle for 
natural selection, in the possession of Rochat as a name. No 
shigle plant, and no single owner of a name, of course, can 
become established anywhere without passing through the sieve 
of natural selection, but that is its chief action. The effect of 
selection upon a name, or upon a species, will be the sum of 
its effects upon the individuals, and one must remember the 

Age and Area is very strongly indeed in favour of differentia- 


It will commonly be found, in studying the distribution of the 
species of a genus, especially if it be of small or moderate size, 
that they are more densely congregated towards the centre of the 
distribution of the genus, and fall off gradually towards the 

150 TEST CASES [ch. xiii 

edges, so that when one draws a Hne round the outermost locaUties 
of each species one obtains a picture not unlike that which is 
called a contour map by the geographers, such as may be seen in 
any good guide-book to hilly country. If the genus be small, 
there will probably be only one generic centre, whilst the larger 
that it becomes, the more broken will the central part be, with, 
more and more regions in which there is a concentration of 
species, like regions of the higher peaks in a geographical contour 
map. So long as a genus is of small or moderate size, the outer- 
most or boundary species seems usually to be one species only, 
but as it grows larger it becomes rarer for there to be one species 
occupying the whole generic area, and one begins to find local 
concentrations of species in widely separated parts of the world, 
like that which is shown here in the map of New Zealand, with 
the species of Ranunculus there found. Here one finds three 
"wides" (as I have called the species which have a dispersal 
outside the country in question) occupying the whole area of the 
islands of New Zealand, and also reaching eastwards to the 
Chatham Islands, 375 miles away. Their distribution is thus by 
far larger than that of any other buttercups in New Zealand 
(fig. 9). The fourth wide has a distribution not very much less 
than that of the most widely dispersed endemic. The total length 
of the islands is 1080 miles and the breadth does not vary very 
much from 100 miles, so that the longitudinal range may be taken 
as a reasonable measure of the dispersal of a species. The en- 
demics are evidently crowded together rather south of the middle 
of the South Island, whilst they fade out completely before the 
north end of the North Island is reached. Of the twenty-eight 
endemics, ten have a range not exceeding 60 miles of the length 
of New Zealand. If one take the ranges in differences of 200 miles 
— 200, 400, etc. — one finds that fourteen, seven, five, one, one 
species have these ranges, or, in other words, the figures form the 
usual hollow curve of distribution, and this is shown by any New 
Zealand concentration of the larger genera. The general impres- 
sion that one gains from a map like this is that the genus 
Ranunculus entered New Zealand probably from the south, and 
at some place in the southern half of the South Island, where the 
incoming species began giving rise to endemics, and on the average 
each species, wide or endemic, spread to the distance allowed by 
its age, and suitability to the conditions with which it met. 

The same type of contour distribution is shown by the genera 
of a family, as fig. 10 shows. Incidentally, these contour maps 


¥\g. 9. Diagram showing the areas occupied by species of Ranunculus in 
New Zealand. Wides dotted; extension East includes Chathams. 

(By courtesy of the Editor, Annals of Botany.) 

















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• *-H 






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r™ ^ 




{- bXj 
o C<J 





show the absurdity of trying to draw a definite line of distinction 
between endemic and non-endemic. 

Working upon the theories of Age and Area and of Differentia- 
tion, this distribution is exactly what one would expect to find, 
but it is extremely difficult to account for upon the theory of 
natural selection or of gradual adaptation. On that theory the 
widely dispersed things are supposed to be the best adapted. But 
to what? It is clear that if the distribution is very wide, each 
individual or group of individuals found in any small region can 
only be adapted to that region. Suitability to other regions that 
differed to some extent from the first could not be such an advan- 
tage to a species that it would help it to settle in the first region. 
Natural selection, picking out species suitable to A, would not at 
the same time pick out qualities that would suit the species 
to B ; it could not even know, to put it in a kind of personal way, 
that B existed, and that A would gain in area of distribution by 
being able to settle there without further adaptation. A species 
must become adapted in turn to every change of conditions with 
which it may meet, whether differing soil, temperature, moisture, 
or biological conditions, and so on, and when at last it meets with 
conditions that go beyond its possible range of adaptation, then 
it will have met one of the boundaries that limit distribution, 
already fully enough described in Age and Area. Probably there 
is some kind of limit to adaptation (or it may be only to speed of 
adaptation) in most or all species. Sooner or later they will come 
up against a barrier, most often probably climatic, which they 
cannot pass. But at the meeting place of such barriers, e.g. in 
Ceylon at the junction of the dry with the wet zones, one not 
infrequently finds different species of the same genus, some on 
one side, some on the other. This is apt to suggest that at some 
time and place, one or the other species was becoming adapted to 
one or the other zone, and that some kind of turn of the kaleido- 
scope took place which resulted in the formation of the second 
species, better adapted to the new conditions, though its morpho- 
logical differences probably had nothing to do with physiological 
problems, but were perhaps in some way a correlation. 

The general evidence of contour maps, of which a very good 
example {Beta) may be found in Nat. Pflanzenfamilien, 2nd ed. 
vol. XVI c, 1934, p. 461, is entirely in favour of differentiation and 
age and area. It is sometimes suggested that at the centre of a 
contour map the conditions are more varied, but very little 
thought is required to show the absurdity of this contention. The 

154 TEST CASES [ch. xiii 

conditions in Britain are perhaps more varied than in any part of 
Europe, yet no genus has the centre of its map there, and several 
hundred genera have the one marginal species in Britain, and that 
only. If this conception were correct, the variety of conditions 
would tend to increase away from the sea. If one take family 
contours such as those shown in the map of Menispermaceae on 
p. 152, the case is even better marked. Such families as Umbelli- 
ferae or Cruciferae have their centres of aggregation well marked 
in the Eastern Mediterranean and Central Asia. But not only do 
they show there the maximum of species in general, but also the 
maximum number of monotypic genera with one species only. 
These are usually set down as relics, and why should relics be 
most numerous at headquarters? In their anxiety to prove the 
validity of natural selection people have worked upon more or 
less independent lines, which often clash badly with one another. 
Workers with floras of islands or of mountain chains have urged 
the conception of endemic species and monotypic genera as relics, 
regardless of the fact that other workers have shown that these 
relics are most abundant at the "headquarters" of the family, 
and are regarded as showing the great suitability of the family to 
that particular region. 

A very difficult problem for supporters of the idea that condi- 
tions and their variety have anything to do with the contours is 
provided by their behaviour in New Zealand. The northern inva- 
sion of plants shows contours beginning in the north, with the 
last species of the genus somewhere in the south. The southern 
invasion begins in the south, and its contours fade away to the 
north, but each invasion passes over the centre of the other 
(where the conditions are supposed to be so varied) without 
taking the least notice of it. There cannot be conditions that only 
affect northern plants, or only southern, as the case may be. 


This case has already been published, and the following descrip- 
tion is largely quoted, by kind permission of the Linnean 
Society, from a paper in their Proceedings of 21 April 1938: 

Whilst when first published both these conceptions — Differen- 
tiation and Young Beginners^ — were much opposed to current 
beliefs, there is no doubt that the latter, at any rate, is gaining 

1 I.e. the conception that the bulk of the very local endemic species, 
especially in warmer countries, are young species starting life. 


ground, as may easily be seen by looking at various recent 
publications in systematic botany, where a great part of the 
endemic species are now admitted to be new. The first conception 
is also beginning to receive support. Systematists have in recent 
years made important additions to the evidence for mutational 
origin of species and genera, though themselves only trying to 
place these species and genera nearest to those which appear 
to be most closely related to them. 

If one take as illustrations some of the more recent mono- 
graphs in Engler's "Pflanzenreich", one notices at once the great 
geographical separations of closely allied species, genera, sub- 
families, families. In Cardamine, for example, species no. 70 
is in New Zealand and Polynesia, no. 71 in the Azores, no. 72 
in Chile. In Euphorbia one finds allied species in Venezuela and 
Cape Colony, in Persia and in Africa, in central Asia and in N. 
America, and so on. If in the Drabeae (of Cruciferae) one join 
the consecutive related genera by a line, one crosses the Atlantic 
five times and the Pacific once, and usually goes well into the 
continent also. In the Arabideae the crossings are seven and 
six respectively, and in the Lepideae the whole map is covered 
with a web of lines. 

Now with relationship like this, which is so much complicated 
by the great separations over the surface of the globe, to get 
an explanation by the method of accumulation of small differences 
is an extraordinarily difficult matter, and it is much simpler to 
call in the Unking genera that cover the enormous gaps than to 
suppose that the related genera, say in Chile and Siberia for 
example, once overlapped or nearly overlapped each other, and 
that then destruction took place upon an enormous scale, and 
through all varieties of conditions and climates. All three of 
these subfamilies have various genera that cover the whole or 
much of the range, and it is much simpler to regard these as 
connecting links — as in fact the ancestors, directly or at times 
indirectly through intermediate genera, of the small scattered 
(though so often closely related) genera. One may take any view 
one pleases as to how they were derived from these large and 
widely distributed linking genera, though personally I hold to 
the views expressed in 1907, when pointing out how all the 
existing Dilleniaceae might have been derived, directly or in- 
directly, from Tetracera, the most widespread and about the 
simplest of the family. The only necessary thing is to get rid of 
the idea that small genera and species of restricted area are 
necessarily relics, and we have seen that this conception is now 
definitely losing ground. 

If one suppose a genus to give off new species more or less 
in proportion to the area that it covers^ (which again will be 
more or less in proportion to its age among its peers), it is clear 

^ For the mathematical consideration of the question, cf. Yule in Phil. 
Trans. B, 213, 1924, p. 21. 

156 TEST CASES [ch. xiii 

that all the offspring will carry a large proportion of the cha- 
racters of the parent, and that therefore while offspring arising 
near together will be most likely closely to resemble one another, 
there is no reason why a close resemblance should not arise 
with a wide geographical separation. 

It is rare to find a genus going far outside the limits of the 
genus that may be looked upon as the linking genus (e.g. Draba 
in Drabeae). When it does, one may imagine that in its " make-up " 
there was included a greater suitability to conditions that may 
be a barrier to the parent — it may be capable of growing in 
warmer (or colder), wetter (or drier), or otherwise different 

The author is not attempting to set up this " parent and child " 
theory as a universal rule, nor at present attempting to apply 
it to zoology; but there is no doubt that it will apply very well 
to most of the small families of plants, to a great number of the 
larger families, to a great number of the subdivisions of families, 
and to a great number of genera whose species behave as do those 
genera that we have been dealing with. 

The theory of accumulation of small differences makes many 
of these and other phenomena very difficult to understand. To 
get two closely related genera or species so widely separated 
geographically by aid of the selection of small differences would 
be very difficult, for one would have to assume — if the differences 
be regarded as adaptational — that the conditions in the two 
places were very similar, though there is little evidence to that 
effect, or that the genera once touched one another in their 
distribution, and that there has been a vast amount of destruc- 
tion. Not only so, but this destruction must have gone on through 
every variety of conditions to which the genera must have been 
adapted. There is some change and variety to be passed through 
between Greece and California, for example, or between Persia 
and Cape Colony, to take a couple of examples from the Lepideae. 

It is probable that cytological study will throw some light 
upon this difficult problem and it is clear that what has been 
said here is fully in favour of the theory of differentiation, 
affording no support to that of natural selection. 


We have seen (p. 18) that the Podostemaceae and Tristichaceae, 
growing in the most uniform conditions that it is possible to 
imagine, yet show a very great variety of character and of 
structure. And not only so, but the characters are at times very 
definitely divergent, such things showing as bilocular and unilo- 
cular ovary, one stamen or two, many seeds or two to four, and 


so on. There are about forty well-separated genera, with well- 
marked characters of flower and fruit, as well as strongly marked 
structural characters of the vegetative body. It is impossible to 
suppose that such structural characters as a bi- or uni-locular 
ovary can matter in the struggle for existence to a family like 
this, whose life is passed under water, the flowers only appearing 
a few days before their final death. The flowers in Asia, and to a 
considerable extent elsewhere, are fertilised by wind, so that 
their structural features are even less important to them than 
usual, though they mostly show the extreme of zygomorphism 
and stand rigidly vertical. The fruits produce a vast mass of seed, 
among which perhaps one in ten thousand may produce a new 
plant. The seeds have no adaptation for clinging to the rock, so 
that the survivors must be determined by chance. 

A great many other families also show great variety in form 
though living in conditions that are comparatively uniform. 
Larger families are in general found to be living in a greater 
variety of conditions than small, but there are no general rules. 
But to co-ordinate the number and variety of the genera and 
species with the variety of the conditions was always an in- 
soluble problem until it was shown that mere age had a great 
deal to do with it. With few exceptions, the older a family was, 
the greater the variety of conditions that it occupied, but there 
was no arithmetical relation between the two. 

We may take a few examples of families and genera that show 
a considerable variety in themselves, without occupying a cor- 
responding variety of conditions. Pandanus, which is found 
almost entirely in the uniform conditions of seashores or marshes, 
has 180 species. The Naiadaceae (1 genus with 35 species) and the 
Aponogetonaceae (1/25) are water-plants of very uniform condi- 
tions. The Cyperaceae, mostly in swamps or in sandy places, both 
of which must be very uniform, show 85/2600. The Bromeliaceae, 
epiphytic or on rocks, and therefore in very uniform conditions, 
are 65/850, the Juncaceae, in damp and cold places, 8/300. The 
orchids, largely epiphytic, where the conditions must be very 
uniform, are 450/7500. The Salicaceae, mostly mesophytic trees, 
are 2/180, the Loranthaceae, woody semi-parasites, are 30/520. 
The Balanophoraceae, internal parasites, whose conditions must 
be very uniform, show 15/40, and Orobanche, a semi-parasite, has 
90 species. The halophytic Chenopodiaceae have 75/500, the 
xerophytic Aizoaceae 20/650, the water-inhabiting Nymphaea- 
ceae 8/50, the insectivorous marsh-loving Drosera has 90 species. 

158 TEST CASES [ch. xiii 

Nepenthes has 60, all living in very much the same conditions. 
Begonia, mostly in the undergrowth of damp forests, has 750, the 
xerophytic Crassulaceae 25/1500. Impatiens, mostly in the moun- 
tain flora of India and Ceylon, has 350 species. There are six 
species of Sonneratia, all mangroves, whose conditions of life 
must be the saine. And so on. From these one can work down- 
wards through smaller and smaller families, showing less and less 
variety, down to single species like Hipjyuris vulgaris of family 
rank. The smaller the family, on the average, the smaller is the 
area that it occupies (size and space, p. 113 of Age and Area). 

Perhaps the most striking example of a great number of species 
all occupying practically identical conditions is the existence of 
the great group of the Fungi, more especially those that are 
internal parasites, where the conditions must be exactly the 
same, except for the chemical differences in the sap of one host 
and of another, differences which must be discontinuous, as the 
different chemical substances that occur are discontinuous. The 
eight genera Clavaria, Fonies, Marasmius, Miicor, Penicillium, 
Peronospora, Puccinia and Saccharomyces, all living in extremely 
uniform conditions, have 2500 species among them. 

As in related forms the number of species goes up with the age 
and distribution of the genus or family, it is much simpler to 
look upon it as going simply with the age — the larger genus or 
family, with the larger distribution, is the older. If the conditions 
also become more varied with increasing age of the family, as they 
almost always do, this probably helps to increase the number of 
species by the stimulus that it gives. There is nothing to be 
extracted from the figures that will go to show that natural 
selection, or variety of conditions, is responsible for the numbers 
of forms that exist. Probably as time goes on, and at any rate if 
there is any stimulus, evolution has to go on. 



A proposition very difficult of explanation is put before the sup- 
porters of natural selection by what is a very common type of 
distribution, long ago pointed out by Dr Guppy in the islands of 
Polynesia, and by the writer in India, Ceylon, and elsewhere. 
This is the polymorphous widely ranging species, accompanied 
by few or many species confined each to one part only of its 
range, and endemic to the regions that they occupy. Guppy noted 
three stages in the development of local endemism. First, the 


island was occupied, so far as a given genus was concerned, by 
one or more widely ranging species, usually very variable, such for 
example as Metrosideros j^olymorpha. Then the wide-ranger was 
accompanied by one or more local endemics, allied to it, and 
finallv there were onlv the endemics. He thousrht that the wide- 
ranger had given rise to the endemics, and might, or even did, 
ultimately disappear (swamped, cf. 66, p. 95) (cf. 74, pp. 611- 

It is the general experience of systematists that it is only in 
numerous and widely ranging forms that this variability occurs 
(cf. p. 132 for axioms). Linnaeus (12th ed., ii, 324) gives a list of 
thirty such polymorphous genera, including willow and saxifrage 
in Europe, oak and Aster in North America, Cactus in South 
America, heather and everlastings at the Cape. 

Another way to bring out this point is to look at the synonyms 
in generic indices like the Index Kewensis. The first forty-five 
generic synonyms at the beginning of C are referred to genera of 
an average size of 94, the mean for all genera being 14-15. The 
first seventy in de Dalla Torre's Indea; are merged in genera with 
an average of 70, or in both cases definitely large genera. 

Let us begin with the Indian Anemones, which show 

A. rivularis All mountains of India and Ceylon 

rupicola Kashmir to Sikkim 

vitifolia Himalaya, Mishmi Hills 

Griffithii Sikkim, B ho tan, Mishmi 

Falconeri W. temperate Himalaya 

ohtusiloha Temp, and alpine, Kashmir to Sikkim 

rupestris Alpine, Kashmir to Sikkim 

trulUfolia Sikkim to Bhotan 

demissa Alpine, Sikkim 

polyanthes Kashmir to Sikkim 

tetrasepala Western Himalaya 

elongata Garhwal, Nepal, Khasias 

Or take Clematis, § Cheiropsis; C. montana is common all along 
the Himalaya, while C. napaulensis, C. barbellafa and C. acut- 
angula are confined to particular sections. These two genera are 
simply the first that occur in the flora, and almost any Himalayan 
genus will show the same thing, whilst it is also shown by the 
genera of lower levels, e.g. Portulaca: 

P. oleracea All India and Ceylon, and all warm countries 

quadrifida All India and Ceylon, and palaeotropical 

WighUafia Carnatic to Ceylon. Endemic 

tuherosa Behar to Ceylon. Endemic 

siijfruticosa W. Peninsula, Ceylon. Endemic 

160 TEST CASES [ch. xiii 

Other genera, e.g. Amoora, Celastrus, Hippocratea, Leea, Limacia, 
OIcLV, Salacia, Tinospora, Zizyphus, from the first volume of 
Hooker's Flora, show the same thing. Clarke (4) says that in 
the Himalaya closely allied species of Didymocarpus are confined 
to single districts, though there appears no reason in soil or 
climate why they should not spread to adjoining valleys. 

Now to explain such phenomena as these by aid of natural 
selection is very difficult. The range of the wide-ranging Anemone, 
for example, is put down to its "adaptation", though to what 
exactly it is adapted is not explained. If it suit (as it does, place 
by place) the very varied range of conditions in which it is found 
that must be due to functional or physiological adaptation as it 
moved from one region to another. We have no evidence that a 
seed from say Ceylon would at once suit a station in the north- 
west Himalaya, without first acquiring the necessary local adap- 
tation which it would have received as a matter of course had it 
been slowly transported from place to place by nature's method. 
But it would then, in all probability, cease to be fully suited to the 
Ceylon habitat. But why should it be accompanied by eleven 
local species? All these are endemic to their own regions. In 
their anxiety to disprove my contention that such local endemics 
are young species as compared with the wide-rangers, my 
opponents have gradually pinned their faith to relicdom. But 
why should A. rivularis leave eleven defeated relics in its range 
of distribution? It looks as if selection had been very strenuous, 
and was greatly diminishing the number of species, not increasing 
it (p. 90). There is absolutely nothing to prove that any of them 
are relics, and no feature in A. rivularis that gives even a faint 
suggestion that it may be adaptationally superior. It covers all 
the mountains of India and Cevlon, and whv are there no local 
relics in any of the southern mountains? None occur south of the 
Khasias. But there can be little doubt that Anemone advanced 
from north to south in the Indian region, reaching Ceylon last of 
all, so that it would be younger in the south than in the north. 
By the theory of age and area, its peculiarities are at once ex- 
plained. A. rivularis arrived first somewhere in the Himalaya, 
where only the local endemics are to be found, and it has not been 
long enough in the southern mountains to mutate off new en- 
demics there. The relic explanation is altogether too fanciful to be 
accepted, as is also that of local adaptation, which also will not 
explain the crowding together of the endemics in the north. 
Nothing hitherto proposed with the exception of age and area 


is capable of explaining problems like these, which occur in 
hundreds and all closely similar. Natural selection is completely 
incompetent to do so. What Anemone shows in the Indian region 
is a contour map, which we have already shown on p. 149 to be 
completely favourable to differentiation and to age and area. 


One cannot accept the large genera as the most successful in the 
light-hearted way in which this has been done under natural 
selection. They are not usually composed of numbers of widely 
distributed species — their successes are limited to comparatively 
very few. We have seen above how few of the numerous Siparunas 
or MolUnedias are widely distributed, and yet these are by far 
the largest genera in their family. And the same phenomenon is 
almost universal. If we take as another example the Styraceae, 
of which the monograph is lying beside me, we find a family of 
six genera, four with three species each, one with two, and Styrax 
itself with 100. Here surely is a family with one conspicuously 
successful genus. But when we look at the whole distribution, 
there are only four widely dispersed species in the whole family, 
one in Pterostyrax and three in Styrax. The distinction between 
these genera is mainly that one has a superior, the other an in- 
ferior, ovary. Upon the hypothesis of natural selection, therefore, 
the family consists of about four successful species and 110 relics. 
And not only so, but the Styrax that is by far the most widely 
dispersed has a very discontinuous distribution (W^. As., Eur.; 
W.N.Am.), a thing that does not occur with the small genera, 
usually looked upon as relics. It is much simpler to regard the 
widely distributed species as older, the local as younger, as differ- 
entiation requires. 



This is sometimes advanced as a corollary of the theory of 
natural selection, and indeed it seems almost necessarilv to 
follow. How much substance there is in the argument, however, 
may be judged from the fact that the most constant characters 
in plants are notoriously those that are the most important in the 
classification (for the obvious reason that they are the most 
constant). But the higher one goes in the classificatory characters, 
from those of species to those of families, the more constant do 


162 TEST CASES [ch. xiii 

the characters become, and the less functional value do they 
have, as is universally admitted. This test is entirely against 
natural selection, even if it do not specially favour differentiation. 



A feature in geographical distribution to which Hooker called 
attention in 1888, and Avhich was never explained until Age and 
Area gave the key to it, is described in the following quotation 
(18): "The conditions which have resulted in Monocotyledons 
retaining their numerical position of one to four or thereabouts of 
Dicotyledons in the globe and in all large areas thereof are, in the 
present state of science, inscrutable." The exactness of the rela- 
tion is remarkable. The latest figures in the writer's possession 
add up to 36,639 species of Monocotyledons and 145,718 of 
Dicotyledons, or almost exactly one to four. 

So long as one keep to large areas, and to the centre of the land 
masses, the relation keeps wonderfully steady, but when one 
comes to the edges of vegetation, especially to the north or to the 
south, one finds fluctuation beginning, as also in the tropical belt 
from Malaya (which has 26 per cent of Monocotyledons) through 
Ceylon (27 per cent). While the average proportion is just 20 per 
cent, and in the Kermadec Islands north of New Zealand is 21 per 
cent, it is 31 per cent in the Chatham Islands to the east of New 
Zealand, and 45 per cent in the Aucklands to the south, and again 
26 per cent in Juan Fernandez and 30 per cent in Tasmania, all 
these figures suggesting that the old southern continent was a 
great home of Monocotyledons. In Europe there is a belt of high 
proportion of Monocotyledons from Sardinia through France and 
Britain to Iceland. In the Canaries the proportion is only 15 per 

Now there is no " monocotyledonous " mode of life to which 
this group can have been adapted. Every kind of life is repre- 
sented, and there is nothing in common in mode of life between 
such things as orchids, grasses, lilies, aloes, bulrushes, water- 
soldiers, palms, aroids, duckweeds, rushes, Bromeliads, yams, 
bananas, gingers, etc. The steadiness of the proportion of Mono- 
cotyledons to Dicotyledons goes to show that in their dispersal 
adaptation played but a small part, and that it was primarily 
governed by the laws of age and area, as is demanded by the 
theory of differentiation. 



If the differentiation explanation of the origin of a family be the 
correct one, the first two genera of a family, the largest upon the 
whole, should overlap in their distribution, as one of them sprang 
from the other, but there is no reason why this should be so under 
natural selection. Geological or other changes may, of course, at 
times have rendered this impossible. Upon examination, we find 
that in the majority of families this overlap does occur, though 
there are a number of families like the Apocynaceae with a large 
genus in each of the continents, or in the Old and New Worlds. 
Exceptions are frequent among the families of the southern 
hemisphere, with their broken areas of distribution, but in the 
greater number of families the rule holds. Among the small 
genera in a large family, this is rarely the case, but in a small 
family it usually occurs. It is not impossible for a grouping like 
this to have been produced by natural selection, but there must 
have been something upon which it could get a grip, and one can 
scarcely ever find anything of this kind. 




X HE results to which this work leads being somewhat sub- 
versive of current opinions, it wiU be well, perhaps, briefly to 
restate parts of the argument in other words. Some of it appeared 
eighteen years ago in Age and Area, but the propositions there 
put forward were not accepted, though the arguments brought 
up against them appeared to the writer to be lacking in logical 
force, and he has remained faithful to his published opinions. 
Bateson alone among reviewers realised that the discovery of the 
"hollow curves" was one of importance, and the only thing that 
opponents have been able to bring up against them is that they 
are "accidental", just as the curve of names from the telephone 
book, or of the names in Canton Vaud (p. 35) is "accidental", 
which is exactly what the writer was out to prove. 

Until some eighty years ago, the appearance of the vast 
numbers of forms of life that people the world, and that are 
usually known as the species of animals or plants, was put down 
to a somewhat crude intervention of the Supreme Power, which 
was supposed to have created all the hundreds of thousands of 
them, each species in its existing form, and to have placed each 
in a more or less definite region, where it is still commonly to be 
found (p. 2). When studied in more detail, however, many 
difficulties cropped up, difficulties that became ever more insis- 
tent, and that at last resulted in the sweeping away of the old 
theory of special creation, then the background of biological 
work. One great difficulty, for example, was to explain the 
evident likenesses that one may see in the tiger, the leopard, and 
the cat, or the daisy and the sunflower, resemblances so great 
that they seemed to point to definite relationship, as indeed had 
been suspected since the days of Aristotle. 

In 1859, with the appearance of the Origin of Species, there 
began the long reign of " Darwinism ", lasting to the present time. 
Darwin's immortal service to science was to establish the theory 
of evolution — that every living species has been derived from 
some other by direct descent, accompanied by such modification 
that for example the tiger, the leopard, and the cat might all be 
derived from a common parent sufficiently far back. Unfortu- 
nately the name of Darwinism was popularly given rather to the 


mechanism by which these changes were to be effected, i.e. to the 
struggle for existence that was a famiUar everyday experience, 
allowing those gifted by nature or by parents, or by chance, to 
succeed, while the non-gifted usually failed. As every living 
being tends to produce more offspring than there is room for, 
some must obviously be picked out, and this selection, or 
"survival of the fittest", Darwin called natural selection. Being 
so familiar, it had a great psychological appeal, and was soon 
taken up in all directions. It was evidently an almost complete 
reversal of special creation ; instead of being created, beings were 
evolved, and instead of being discontinuous, the process was 

Picking out only variations that gave some advantage, natural 
selection worked by what we may call gradual adaptation 
(p. 4), which was an essential feature of the theory. But it is 
clear that a small improvement in adaptation would not be 
enough to create a new species, which is usually more or less 
sterile with its near relatives (a functional difference), and shows 
various structural differences as well. It had to be assumed, 
therefore, that the process would go on until the line of mutual 
sterility had been passed, and the differences had become great 
enough to mark it as a new species. It was the structural dif- 
ferences that showed that there had been any evolution at all, 
and so it had to be assumed also that they were adaptational, 
marking the adaptational advantages that had accrued to the 
organism. Functional adaptation was ignored, though the mor- 
phologists had long insisted that structure had little or nothing 
necessarily to do with function. 

The freedom of the position of natural selection was really lost 
very early in its history, when Darwin had to give way to the 
criticism of a well-known professor of engineering, Fleeming 
Jenkin, who pointed out that unless a great many individuals 
varied in the same direction over the whole of a considerable 
area, the improvement would promptly be lost by crossing. 
Darwin therefore stipulated for such a beginning, which seems 
only likely to happen under the action of some external force, and 
which practically excludes the action of biological factors, which 
are usually local. Improvement seemed unlikely in the fluctuating 
variation upon which Darwin usually relied, for some might go 
up when others went down, and crossing would level them. This 
criticism took much of the spring out of the action of natural 
selection, for instead of remaining a simple affair of individuals, 


as it was in daily life, it was assumed to be a competition of 
groups. Whatever may be the case with animals, there seems 
little or no reason to imagine that plants compete as groups. It 
is this assumption which has become so marked a feature in 
social and political life — that the best, and incidentally the most 
satisfactory, solution of a difficulty or of a competition lies in 
the conquest and dominance, or even in the extermination, of the 
opponent. Species, to begin with, are not structural units with 
all individuals just alike, any more than are language groups of 
mankind. The nearest approach to this condition is in such cases 
as Coleus elongatus (p. 24), a well-marked "Linnean" species 
where there are so few individuals — perhaps a dozen in this case 
— that they do not allow of a great range of variation. There is 
also less range in the small "Jordanian" species, but these, on 
the theory of differentiation, are later phases in evolution than 
are the Linnean species. As one of the latter increases in number, 
and in occupied area, from its first beginning, and thus probably 
comes into greater variety of conditions, and into more crossing 
with other individuals, the more variation does it show, on the 
whole (p. 159). 

The following quotation shows the point of view that is being 
taken up as the result of the work of agricultural geneticists; 
*' Studies of crop populations have shown that natural selection 
does not result in the survival of the fittest type, but of the fittest 
'population, and the fittest population is almost always a mixture 
of many types" (78). This agrees with the ordinary observation 
of everyday life, that natural selection is individual in its action. 

The plants (or group, occupying the whole of the locality) that 
did not show the useful improvement (or another as good) were 
killed out in the struggle for existence, that also killed out the 
parent, which was assumed not to become adapted. 

It is clear that there are many weak points in the Darwinian 
position, and to support them all kinds of assumptions and sup- 
plementary hypotheses have been brought up. But there has 
never been any good proof (1) that evolution proceeded essen- 
tially by improvement in adaptation, (2) that it was gradual and 
closely continuous, (3) that the phenomena of the structure of 
plants reflect the adaptation that has gone on in them, or (4) that 
groups of plants can compete as units. 

When one comes to look into the matter, one soon realises that 
the theory of natural selection rests upon a great many assump- 
tions, sometimes backed by more or less proof, sometimes not. 


Yet I have been assured by one of its most eminent supporters 
that it contains none, but rests upon proved facts. The following 
list gives the most important assumptions : 

1. That a small structural variation may be advantageous 
enough to call in the action of natural selection (pp. 4, 13). 

2. That a small advantageous variation may be inherited 
(p. 4). 

3. That it mav be added to, and become more and more 
marked in succeeding generations (pp. 4, 54, 106, 165). 

4. That the whole number of individuals upon a considerable 
area will show the same advantageous variation, i.e. probably. 

5. That the variations are controlled by external conditions 
(pp. 5, 165). 

6. That the whole number of individuals carrying a useful 
variation can, and does, fight as a unit (pp. 107, 142, 144, 166). 

7. That the parent form does not also become adapted 
(pp. 4, 13, 54). 

8. That adaptation is structural rather than functional 

(p. 4). 

9. That structural characters are the means of expression of 
adaptation (p. 14). 

10. That differences in structure mean differences in adapta- 
tion (pp. 52, 109). 

11. That the variety with the advantageous variation, slight 
though it would be at first, will defeat the parent in the struggle 
for existence (p. 4). 

12. That the new form produced by natural selection, and 
adapted to area B, became thereby also better adapted to A, the 
area occupied by the less well adapted parent species (p. 144). 

13. That all variations that survive must be useful, or must be 
correlated with variations that are useful or at least that are not 
harmful enough to be of serious disadvantage (pp. 57, 58). 

14. That the new form will invade the territory of the old, and 
kill it out there, without being lost in hybrids (p. 143). 

15. That the defeated species w411 gradually become relics, and 
ultimately disappear (pp. 4, 17, 91, 97-8). 

16. That fluctuating variation is irreversible. 

17. That fluctuating variation is qualitative as well as quanti- 

18. That fluctuating, or even small, variations can be added 
up so that they pass the sterility line that usually divides one 
species from the next. 


19. That the needful variations will appear at all (p. 55). 

20. That natural selection can act continuously upon them 
(p. 54). 

21. That most or all of the individuals that do not show the 
favourable variation will be killed out (p. 54). 

22. That conditions will continue to vary in the same direc- 
tion long enough to enable the sterility line to be passed (pp. 54, 55). 

23. That natural selection is so strenuous in its action that the 
sterility line will be passed (p. 55). 

24. That when a species has become well started upon a 
variation in one direction, there will not be offered to it one in 
another direction, obviously better (pp. 55, 109). 

25. That the adoption of one variation does not interfere with 
the adoption of another (pp. 55, 109). 

26. That when one variation has done its work, it shall be 
followed by another of those that mark the species (p. 55). 

27. That morphological and anatomical necessities override 
the effects of natural selection (p. 110). 

28. That economic botany is of no importance from the point 
of view of natural selection (p. 8). 

29. That advantageous structural variations are so desirable 
that they will commonly be followed up to a result of 100 per cent 
(p. 114). 

30. That natural selection will produce uniformity in structure 
of a morphological feature (pp. 55, 114, 124). 

31. That there was some reason why transitions were dropped 
out more and more as evolution went up towards families (p. 113). 

32. That varieties are incipient species, species incipient genera. 

33. That numbers would increase greatly under selection 
(p. 90). 

This is a very formidable list, and a mere glance will show that 
many or even most of the assumptions still remain such, though 
by the adoption of mutation in place of gradual variation several 
of them have been removed. It is, therefore, clear that the 
theory of evolution by the agency of natural selection, picking 
out gradual improvements in adaptation, chiefly structural, is 
still a very long way from being established, and as no evidence 
has been found in seventy-five years to prove many or most of 
the assumptions, one may be permitted to feel somewhat sceptical 
of its discovery. Evolution is now thoroughly well established, 
and whether natural selection carried it on or not is a matter of 
indifference to it. 


The theory of natural selection, holding as it did that every- 
thing was gradually acquired, went to show that evolution must 
be gradual and continuous from one structure to its successor of 
different form, and this soon led to difficulty. The facts of 
economic botany (pp. 8, 89) among others, though dismissed as 
unimportant since they did not favour natural selection, showed 
that there was much discontinuity in evolution, and Bateson's 
work (1) showed the same thing. 

The continuous small fluctuating (infinitesimal) variations upon 
which Darwin chiefly relied were not fully hereditary (p. 10); 
they were not differentiating, but simply up and down in the 
same character, nor were they irreversible; and they could 
not be accumulated beyond a certain point (p. 10). They could 
all but never be found to show adaptation, whilst the differences 
became more and more marked, and less and less adapta- 
tional the higher that one went from species to family, this 
illustrating the principle that we have termed the divergence of 
variation (p. 74). Species, again, usually showed several points 
of difference which were unconnected with one another so far as 
anyone could see, and it was very hard to see how selection could 
deal with so many. Species also proved to be mostly local in the 
big or "successful" genera, so that their adaptation must have 
been generic, and it was very hard to understand how this could 
have been the case. If it were so, natural selection, working 
upwards from the species, could hardly explain it. If all specific 
characters were correlated, then the greater portion of evolution 
did not show the effects of natural selection (p. 11). It was 
almost impossible to see how gradual selection could pass the 
rough and ready line of distinction between species, the fact that 
they are almost always more or less mutually sterile. No transi- 
tion stages, again, were to be found among the fossils, though one 
would have expected to find such upon a theory that was based 
upon the separation of genera and families, to say nothing of 
species, by the continual destruction of transitional forms on 
account of their inferiority to the more perfect. Nor could one 
find among the fossils any indication of the gradual formation of 
existing families, etc. These seem to appear already fully de- 
veloped, and in widely separated sections of the classification of 
flowering plants. 

Evolution could only go on if the right variations were to 
appear; natural selection would kill out any that were harmful, 
and would be indifferent to any that showed neither value nor 


the reverse. Also evolution could only go on provided that 
natural selection could act as desired, another assumption. Then 
the freedom of action of selection was destroyed by Fleeming 
Jenkin's criticism, though the fact was hardly realised. Finally, 
selection proved itself incapable of explaining many of the facts 
of geographical distribution, a subject which is completely 
bound up with evolution. 

Immense effort was put into the study of adaptation fifty to 
sixty years ago (p. 52), but with little or no result other than to 
show that no one in his wildest dreams could attach adaptational 
value to the bulk of the structural characters that distinguish 
one plant from another, and show that evolution has really gone 
on. There was also no doubt that what little adaptation did show 
decreased rapidly as one went up the scale above the rank of 
genus ; but the higher divisions were supposed to be made by the 
killing out of transitions, which would imply that selection came 
more and more into play to make larger and larger divisions. The 
facts, when judged in the light of the theory of natural selection, 
are evidently somewhat incompatible. 

Early in this century de Vries brought in the theory of muta- 
tion or sudden change, which in many respects got over the worst 
difficulties of Darwinism, and would have surmounted more had 
not people taken up a somewhat illogical attitude with regard to it. 
It was admitted that small mutations could take place, but people 
were averse to admitting large ones, for that would probably 
remove any effect of natural selection in guiding evolution. It 
would be almost absurd to suppose that it showed its work by the 
production of large and sudden differences, though it is not im- 
possible, for one may imagine it perhaps selecting slight genie 
changes, and these being added up till the strain in the nucleus 
produced some kind of kaleidoscopic effect by a readjustment. 
The writer suggested in 1907 that "a group of allied species 
represents so many more or less stable positions of equilibrium in 
cell division" (70). But though by the adoption of small muta- 
tions the power as a determinant of evolution was taken away 
from natural selection, so that it could no longer start the im- 
proved adaptations, it was expected to carry them on and to 
increase them, gradually or by further mutation. Of course it 
would only carry on those which had, so to speak, passed through 
its sieve, and had proved to be of definite value. We were still, 
however, without any indication that the characters produced in 
the small mutation had any adaptational value, so that their 
survival would usually be due simply to the fact that natural 


selection was indifferent to them. But if this were so, it could not 
carry them further. This being so, why not go the whole course at 
one effort, and admit that selection had little, or perhaps even 
nothing, to do with the evolution of the organisms that now exist 
in the world, however much it may have improved them after 
their evolution, or fitted them to the local conditions in which 
they were trying to live? Everything, before it can become 
established, must pass through the sieve of natural selection, and 
each new individual, in any place, must do the same, but the 
characters of that new species or individual were not selected by it. 
If selection does not begin a species or an individual, it has no 
responsibility for its arrival, but it will kill it out if it be un- 
suitable to the conditions of the place in which it appears, at the 
time at which it appears. Why then should natural selection be 
needed at all for structural change, if it does not begin it, and 
when one can generally find no adaptational value in it? 

This is very much the position that the author took up in 1907, 
basing his change of view more or less upon this line of reasoning, 
and admitting that no mutation that may be needed for the 
purpose in view — the formation of species, genera, or families — 
is too large for possibility. There is little or no evidence that 
structural differences in root, stem, leaf, flower, fruit, seed, have 
any adaptational value, yet it is these things that make up the 
characteristic differences that separate one species, genus, or 
family from another (cf. Thalictrum, etc., on p. 104, and lists in 
Appendices). There is no evidence that climbing plants (p. 57) 
have gained by the fact that they can climb. The same genus 
sometimes contains both climbers and non-climbers, and the 
former must have erect plants upon which to climb, with few 
exceptions. Supposing that they smothered all the erect plants 
by their success, as they might very easily do if really "suc- 
cessful", both they and the latter would be in a bad way, yet 
there is nothing to prevent it. 

The view that mutations are necessarily small rests to some 
extent upon the opinion that a Linnean species is composed of a 
great assemblage of micro-species which breed true. But it can 
only be so if it consist of a great number of individuals and 
occupy a large area. Upon the theory of age and area, as well as 
upon that of differentiation, this means that it is older than the 
small and local (allied) species, which is so often Linnean in the 
sense of marked difference, but cannot show great variety through 
lack of numbers (p. 132). 

We imagine, then (under the theory of differentiation or diver- 


gent mutation), that families, genera, and species may any of 
them be the result of a single 7nutation, more divergent in genera 
than in species, in families than in genera. These ideas receive 
great confirmation in the actual structural differences that 
separate plants. As one goes up the scale from species to family, 
the divergence of the characters of separation increases upon the 
whole, as is at once shown by any good dichotomous key. A 
feature of special interest is that the divergences become more 
and more such as allow of no intermediates or transitions at all, 
as for example, a berry and a drupe, an achene and a follicle, an 
anther with slits and one with pores. But if this be the case, the 
character, one or the other of a divergent pair, must have 
appeared at one step, so that, so far as one can see, natural 
selection can have had no hand in its appearance. The higher 
that one goes in the direction of the family, the less adaptational 
value can one find in the characters, so that the less is the handle 
that is offered to natural selection. Competition is greatest 
among individuals, less among species, still less among genera, 
and so on upwards. Yet the distinctions become greater along the 
same route, and the puzzling question is put as to how the 
diminished competition can bring about the larger and more 
permanent distinctions. Why also are these characters of so 
slight (if any) functional use? If natural selection be the active 
agent in evolution, it must have been working at its highest 
pressure among the highest groups to separate them as they are 
separated, and also must have been working all the time to pick 
out characters with greater adaptational value; whereas in fact 
one finds the characters to be of less and less value as one goes 
upwards in the supposed track of natural selection. In seventy- 
five years no one has been able to prove any functional value for 
them. The uniformity of the statistics of the various continents 
and other large areas (66, p. 180) in the proportions of genera 
of various sizes, in their distribution, in the relative sizes of 
families and genera, etc., shows that one area is just like another, 
and that evolution must be going on in the same orderly way 
in all. 

Though going to Ceylon an enthusiastic supporter of natural 
selection, the author found it needful to change his views after 
some years of tropical experience, both in the forest, and as the 
result of a minute study of the Podostemaceae (p. 18). Though at 
first glance looking as if they showed great adaptational dif- 
ferences, these plants all live under the most amazingly uniform 


conditions, with nothing special to which to be specifically 
adapted. The life in moving water, and the loss of proper polarity 
of the plant (p. 20), are common to all. Yet there are about forty 
genera with many species. The most reasonable explanation is 
that evolution must go on, with or without adaptational reason, 
and is not necessarily a matter of local adaptation. All are com- 
pelled to "adapt" themselves more or less to the action of the 
permanent force that acts upon them, which cannot be escaped in 
any way. 

The author's work with endemic plants, which has occupied 
many years, also showed that the old (and still more or less 
current) view, that they are relics of previous vegetation, had no 
sound basis. Under the Darwinian theory, there had to be found 
somewhere some at least of the species that had been defeated in 
the struggle for existence and were dying out. The harmless 
endemics just came in conveniently to fill this position, but while 
there are undoubtedly many relics in regions that were cooled in 
the glacial periods, one cannot suppose this of most of the local 
species of warmer climates. 

As one result of this work, the writer discovered the "hollow 
curve" of distribution (chap, iv) that shows in plants and 
animals, and in many other cases, such as surnames, and even in 
inanimate objects (cf. p. 35). It shows well in areal distribution, 
many species of any genus occurring on small areas, few on large. 
It shows still better in the distribution of the genera in a family 
by the numbers of species that they contain. On the average, 
from which there is but small variation, with reasonable numbers, 
about 38 per cent of genera have only one species, 12 per cent 
two, and 7 per cent three. The curve turns the corner between 
three and five, and tapers away in a long tail, and the larger the 
family the more accurately does it follow the curve. When plotted, 
as 38 + 7 make more than twice twelve, the curve has the dip in 
the middle that gives it its name (fig. on p. 36). When plotted in 
logarithms, the curves form close approximations to straight 
lines, showing that all have the same mathematical form, and 
have appeared as the result of the same law, working upon all. 
The mathematical treatment of the subject will be found in Yule's 
paper (75), the introduction to which should be read by all in- 
terested in evolution. The general law, as he showed, that imme- 
diately governed it was that at the end of certain intervals, 
probably very variable in length, a genus became two, and both, 
as a rule, survived. The parent genus of the two was not neces- 


sarily killed out, as was the rule under natural selection. In fact, 
as the curves must be the result of uniform pressure, they could 
not result from, or under, natural selection. 

The logarithmic curve undoubtedly shows some marked devia- 
tions from the straight line at the further end (cf. p. 37), and 
Longley (25) says "the hollow curve, we may therefore reasonably 
assume, results from some sort of compounding of a series of 
geometric series of different common ratio, but all lying between 
the limits of J and 1 ". 

But if genera and species are formed like this, it must almost 
certainly have been by single steps, and if the old ones were not 
killed out, natural selection can have had little or no influence in 
the matter. They cannot have been formed by structural adap- 
tation. Gradual mutational change is no more satisfactory than 
the gradual changes that were supposed to have been effected by 
natural selection, for in the vast majority of cases where such 
small changes have been seen, there has been no possibility of 
imputing to them any functional value whatever. On the Dar- 
winian theory, where the parent is killed out, it is very hard 
indeed to see how there can have been any increase in numbers 
(Test case i, p. 90). 

One great advantage of the large mutations for the formation 
of species, and still more of genera and families, that are de- 
manded by the theory of differentiation, is that at one step they 
will cross the "sterility line", the rough and ready distinction 
that separates a species from its nearest relative. The new form 
will at once become isolated (chap, vii), and there will be little 
likelihood of its being lost by crossing. As we have seen, isolation 
may be of very great importance in the establishment of new 
species, if not also in their evolution. 

When one considers the fact (pp. 132-4) that the more 
primitive things are more widely distributed, that a genus (unless 
monotypic) occupies a wider area than at any rate all but one of 
its species, and again that there is no evidence to show that there 
is any adaptational reason why a small variety should become a 
larger one, or the latter a species, a species lead to a genus, and 
so on, it would seem, as it seemed to (the late) Dr Guppy and to 
the writer over thirty years ago, that we have been to a large 
extent trying to make evolution work backwards. It was in- 
finitely simpler to work forwards throughout evolution, beginning 
always with the family, deriving the genus from that, the species 
from the genus, and the variety from the species. In fact, with 


the absence of adaptational reasons for progress, and with the 
frequent impossibiUty of transitions (especially in the characters 
of the higher groups) it seemed to be almost the only way. 

My friend Dr H. B. Guppy was perhaps the first to call proper 
attention to the fact that the Darwinian theory was trying to 
work evolution backwards. He says (12): "It follows from the 
foregoing remarks that no plant groups, in the sense of the great 
orders, could have been produced on the evolutionary lines im- 
plied in the Darwinian theory" (i.e. beginning with small 
varieties and going through species to genera and families), and 
continues "to lay down, as the Darwinian evolutionist does, that 
the order of development begins with the variety . . . species . . . 
genera. . .families, is to reverse the method followed in nature, 
since it implies that the simpler, least mutable, and less adaptive 
characters that distinguish the great families are the last de- 
veloped. This could never have been. Nature has ever worked 
from the simple to the complex, from the general to the particular. 
Had she followed the lines laid down by the Darwinian school 
of evolutionists, there would be no systematic botany. All would 
be confusion. There would be no distribution in the sense in which 
the term is generally understood, and the plant world would be 
a world of oddities and monstrosities." 

It is upon such propositions and facts that the pre-Darwinian 
theory of differentiation or divergent mutation is now founded. 
Natural selection is no longer to be regarded as the mechanism of 
evolution; it does not choose what shall be evolved, but it decides 
in each case, individually , what shall be allowed to live. Probably 
the bulk of the structural characters make little or no difference 
one way or the other, and so are indifferent to natural selection. 
Evolution ceases to be a mere matter of chance, and comes into 
that scheme of things of which Jeans has said that all the 
pictures which science draws of it are mathematical pictures. 
What causes it to go on we have yet to discover, but we can make 
one important step by finding out in which direction evolution 
moved, for that involved in the theory of differentiation is the 
exact opposite of that involved by natural selection. One goes 
from the family downwards, the other from the variety up, and 
as there is as yet no evidence to show that it moved in one 
particular direction, we are free to take that for which there is 
the better evidence. 

After fifty years of work, the author has come to the conclusion 
that evolution and natural selection work at right angles to one 


another, with but slight mutual interference, the latter being 
quite possibly greater in animals. The evolution provides the 
structurally different forms of life, while natural selection works 
upon the functional side, and adapts them in detail for their 
places in the local biological economy. There is no obvious reason 
why selection should not develop small structural variations, 
though one will not expect specific changes, unless rarely. In 
general, selection will simply kill out those individuals, whether 
new species or not, that commence anywhere with functional 
characters that are unsuited to the conditions of the moment, or 
that simply have ill-luck. Each new species, by mere heredity, 
will probably have functional characters more or less closely 
suited to the place in which it arises, but as time goes on, and the 
number of species increases, chiefly by arrivals from elsewhere, 
more and more careful adjustment will be needed to fit in each 
newcomer. It is in this work that natural selection is of the first 
importance, doing work that nothing else could do with the same 

Whether evolution must go on in all circumstances, we do not 
know, for there is evidence like that of the widespread Hippuris 
that seems to show that it is not perhaps absolutely necessary. 
The evidence of the Podostemaceae seems to show that it may go 
on without change of conditions, though perhaps only under the 
action of a permanent force. If a plant suddenly arise with a 
suitability to any particular mode of life, like a climber or a 
parasite, natural selection will not kill it out, and it may go on 
living, and perhaps do very well. 

As things show more and more definite adaptation to some 
peculiarity of the conditions, they come up sooner and sooner in 
their distribution against actual barriers to further spread, so 
that they tend to occupy lesser areas than older and less adapted 
species, perhaps closely related to them. As we have seen, a 
species may become adapted to many regions, one by one (p. 145) 
as it travels through them, but it need not show this adaptation 
in external characters, nor have we any reason to suppose that 
when it has become suited to B it remains necessarily suited to A. 
It is possible that this functional adaptation, with or without 
isolation, may result in genie changes that may be added up until 
they cause a structural mutation. Admittedly we have not yet 
solved the whole problem of adaptation as one may see it in so 
many characters, but there is no evidence for the gradual adapta- 
tion in structural characters that is demanded by natural selection. 


Longley (26) thinks that it will be found that adaptation comes 

Though natural selection comes more and more into play as 
the species in a given region become more numerous, or as a 
human society becomes more complex, its action is always 
primarily individual. There is little or no competition between 
entire species, varieties, or races (cf. pp. 107, 142, 144). 

The conclusion to be drawn, therefore, is that natural selection 
has not been the driving force under whose influence evolution 
has been carried on, though it has been the selecting force by 
whose action the individuals best suited to the conditions of any 
time and place have been continually picked out. In this way a 
continual adaptation has gone on, and except in casual and im- 
permanent cases, has ensured that the plants that occur under 
natural conditions are very closely indeed adapted to those con- 
ditions. This adaptation is not structural, but functional, as is 
illustrated, to take one example only, by the structural resem- 
blance of the members of a large family growing in a great variety 
of conditions, and the great structural differences of a large 
ecological "association " of plants growing in very uniform condi- 
tions (p. 53). The work of Hutchinson and other agricultural 
geneticists shows that natural selection picks out a mixture of the 
most suitable individuals, not a type, as indeed may be seen every 
day in ordinary life by any observant person, and as is shown by 
the composition of any of the larger nations at the present time. 

There are a great many difficulties which to a logical mind are 
fatal to the supposition that natural selection was responsible for 
the great evolution of living forms that has gone on. Take for 
example the facts of economic botany, always dismissed as 
unimportant since they do not agree with the theory of natural 
selection. The definite similarities and relationships that exist 
among the various products belonging to the same family show 
that whatever was responsible for the production of the family 
must also be responsible for the economic products, while at the 
same time the discontinuity in structure of the latter, and the 
impossibility of gradual transitions between them, shows that 
their evolution must have been by large mutations. The difference 
between the distribution of a family and that of an association as 
given in the last paragraph is another very strong argument in 
the same direction. 

In the second place, natural selection would make the whole 
great process of evolution, including man, the result of chance 

WED 12 


selection of favourable variations, whereas the recent progress of 
the physical sciences goes to show that in their case the whole 
evolution is proceeding upon a well-marked "mathematical" 
programme. The theory that is beginning to be indicated in the 
work that has been described above, goes to show that evolution 
also, one of the greatest recent facts of the physical universe, has 
proceeded upon a course underlying which there is some physical 
law, probably electrical, which also can be expressed in mathe- 
matical terms. This has already been shown to be the case with 
the law of age and area, which is evidently only a corollary of 
the larger law thus indicated. 

To go on to some of the minor objections to natural selection, 
of which there are a great number, it is impossible to explain by 
its aid the characters that divide species, and the difficulty be- 
comes greater and greater as we go up the scale through genus to 
family and beyond, while at the same time the distinctions 
become also greater and greater, and any functional value to be 
attached to them becomes less and less, whilst possible transi- 
tions become rarer and rarer. 

It is almost impossible to explain the perfection in which the 
characters show themselves, a clean-cut perfection which again 
becomes more and more marked the higher we go (p. 76). If 
natural selection cannot perfect either of such divergent charac- 
ters as opposite leaves and alternate (showing a definite phyllo- 
taxy), their perfection must be due to heredity, or to direct 
mutation, for there cannot be a gradual passage from one to the 
other. In the latter case natural selection is excluded, while in 
the former one has to remember that the way in which the 
ancestor obtained the perfect character must be explained by 
natural selection. There is the further difficulty that so often the 
two characters occur side by side in species of the same genus. 
As a special case we may take the family Rubiaceae (p. 118). 
Members of the family can be found showing alternate leaves (as 
against opposite, the "family" character), pinnate (entire), 
intrapetiolar stipules (interpetiolar), male and female flowers (^), 
zygomorphic flowers (regular), solitary axillary flowers (cymes 
or heads), 8-merous flowers (5-4), convolute calyx (open), 
descending aestivation of corolla (convolute or valvate), anthers 
by pores (slits), ovary 10-locular (2), endosperm none (present), 
ruminate (not), whilst the whole family shows an amazing variety 
in the fruit. All the characters that distinguish the family are 
found at times to be replaced by something quite different, 


whilst at the same time no transitions are possible, a fact which 
would indicate that all the characters were due to direct muta- 
tion. How, then, was the family Rubiaceae, whose actual general 
characters are those shown in the brackets, evolved by aid of 
natural selection? If all these vagaries are to be explained on the 
supposition that morphological necessities override selection, 
there is nothing at all of structural nature left for selection to act 
upon. The selectionist is content, and seems to think that his 
case, that evolution is due to natural selection, is proved, if he 
can explain a single, and probably very minor character, upon 
that supposition. He forgets that it also has to explain the corre- 
lated characters of a whole family or other systematic group, to 
say nothing of the great differences that characterise the great 
divisions of the vegetable kingdom like ferns, mosses, and liver- 
worts, as well as the flowering plants. One cannot employ one 
machinery to explain one feature or one portion of the vegetable 
kingdom, another for another. 

There is no evidence to show that natural selection is collective 
in its action rather than individual. It is obviously the latter in 
daily life, and the work quoted on p. 166 shows that it is probably 
the same among plants. It seems, therefore, that once the idea 
that adaptation — ultimately reducible to the chance appearance 
of favourable variations — is mainly responsible for the distribu- 
tion of plants and animals has given way to a more scientific 
conception, the study of plant distribution and of its dynamics 
will become associated to that of human populations, each giving 
valuable aid and assistance to the other. 

Plants seem to behave like a mixed and more or less casual 
population expanding in a country where there are barriers of 
many kinds to interfere with the regularity, and where the dis- 
tribution is determined in detail by natural selection, working 
upon the individuals. The same kind of thing has marked the 
distribution of races in Europe, etc. We have seen that it seems 
to pick out a mixture, not a type, and we may add to this the 
curious fact that has lately been exciting some interest, that one 
kind of cotton may do best when mixed with another (79). 
This fact may have important bearings upon racial intermingling. 
One thing at least seems fairly certain, that a whole group A will 
not conquer and destroy a whole group B, but that the result 
will be an intermingling of the individuals of both that are best 
suited to the conditions at the time and place. 

Nothing but sudden mutation, usually large, will explain why 



the same character, and that in perfection, should so often be 
found at widely separated places in the same family, and not 
only so, but also at numerous places in other families and in 
other classes. There is no morphological difference in a berry, 
whether it be found in the Dicotyledons or in the Monocotyledons. 

Only the conception, which is so largely borne out by the facts, 
that mutations on the whole were larger the further back into 
the past that one goes, from species through genus to family and 
class, can easily explain the remarkable fact that this is definitely 
the case, as both differences, and impossibility of transitions, 
increase together. Neither in life nor in the fossils do we find any 
evidence of serious transitional stages, and it is therefore evident 
that the further back we go from the individual the greater are 
the differences, whereas natural selection cannot be shown to be 
more and more efficient in destroying transitions upon the same 

We have now to consider the actual differences seen between 
organisms. There is no doubt that specific differences are usually, 
but 7iot necessarily, small (p. 79), while generic are on the whole 
larger, though there are large differences between different kinds 
of genera, as for example between those of small families and those 
of large (p. 110). Family differences are on the whole the largest 
of the three. Looking at the list of family characters in Appen- 
dix I, one notices their divergence when taken in pairs — alternate 
or opposite leaves, cymose or racemose inflorescence, and so on. 
Many of these pairs do not allow of intermediates or transitions, 
but this shows less in generic or specific characters. Practically 
all of the family characters, however, may at times appear as 
generic or specific ; there is nothing about a character to place it 
only in one of these classes. In fact, as we have seen on p. 110, 
the rank of genera or of species differs with the size of the groups 
to which they belong. 

One may almost say that a family has a combination of most of 
these "family" characters, though sometimes the one, sometimes 
the other, of any particular divergent pair. The important points 
are this divergence, and the fact that the character is shown in 
full perfection (p. 114), a feature that one would certainly not 
expect under the operation of natural selection, for the adapta- 
tional value of the character would diminish as it approached 
perfection, and probably 95 per cent or less would be as good as 
100 per cent. It is all but inconceivable that selection should 
produce perfection in a character, especially one like most 


structural characters, in which one can neither find nor imagine 
any adaptational value whatever. 

If differentiation be accepted, the process of evolution may be 
quickened up considerably, for a single mutation may effect in 
one step a change which might take an immense time under the 
action of natural selection, especially when one fully realises that 
the vast bulk of structural differences have no adaptational value. 
And if, as upon this view would seem highly probable, mutations 
were, on the whole, larger as one went further back into past 
times, the difficulties of explaining the origin of great groups like 
the ferns will be greatly lessened. It must not be forgotten that 
these also must be explained by natural selection, which as yet 
has shown itself quite incompetent in this respect. So long as we 
try to explain these by adaptational changes, or by dying out of 
transitional stages, so long shall we be in great difficulty. The 
theory of divergent mutation requires nothing of this kind, and its 
capacity of explanation is far greater than is that of the theory of 
gradual adaptation. It seems to the writer that the theory of 
natural selection leads to too many untenable positions to be any 
longer acceptable, and that differentiation, working downwards 
towards the species, and by large mutations, diminishing as one 
comes downwards (on the whole) should take its place. 

The evidence is clearly in favour of differentiation, or diver- 
gent mutation, rather than natural selection. The largest and 
most divergent mutation gives rise on the whole to the family, 
while the later and usually less divergent ones give rise to the 
later genera and species, which come as a rule within the limits 
marked out by the first. This agrees completely with the familiar 
fact that the key to a family can be so easily made upon these 
lines, with the largest differences coming first, followed by 
smaller and smaller ones down to the specific and varietal dif- 
ferences at the bottom. But this feature is a matter of extra- 
ordinary difficulty to explain upon the Darwinian theory, under 
which two species form by progress in gradual adaptation in 
slightly different directions, the unmodified and the transitional 
forms being killed out, until at last the difference is so great that 
they have become new species. But if a slight variation in a 
favourable direction is enough to give an advantage over the 
forms that have not varied, what is to be gained by going on with 
the variation until it becomes specific, and how is this to be done? 
What adaptational need made one species adopt an alternate 
leaf with a phyllotaxy of 5/8, its nearest relative opposite leaves? 


Nothing but sudden mutation can account for such differences, 
and natural selection has probably nothing to do with it. It 
sorts the products of evolution into their most suitable places. It 
is as if the evolutionary train dropped a passenger or two at 
every station, who has then to make good in the particular 
conditions that there obtain, in the society or community in 
which he happens to find himself, and with the equipment for 
the task that he happens to carry with him. 

But if differentiation or divergent mutation be the more correct 
explanation, it is clear that evolution moved in a direction the 
opposite of that in which it would move under natural selection. 
The latter works upward /rom the small variety, which is assumed 
to be an incipient species, whilst the former works downward to 
the variety. The latter, under differentiation, represents the last 
ripple of the disturbance which gave rise to the family, not the 
first ripple which is to give rise to a disturbance becoming ever 
greater and greater. Natural selection kills out the ancestor and 
the transitional forms, differentiation does not kill the ancestor, 
nor expect transitions. 

The question as to which explanation is nearer to the truth, 
therefore, may be settled by an answer to the question as to 
which was the direction in which evolution moved. To obtain 
this answer, the author has devised some thirty-four test cases, 
given in Chaps, x-xiii, and as all of them give good, and a number 
give very strong, if not convincing, evidence in favour of the 
direction required by divergent mutation, it becomes in a high 
degree probable that this is the more correct explanation, and 
that natural selection had little or nothing to do with the fact 
that evolution went on. 

There is some other law behind the latter, which at present we 
do not understand, though probably when we learn what is the 
driving force in cell-division, we shall be nearer to the goal. My 
friend Dr Charles Balfour Stewart suggests that the law is 
probably electrical, and that perhaps the development of a new 
form may have some relation to the transfer of energy in some 
way. The divergence of mutation may perhaps become a little 
less unintelligible by some explanation of this kind. 

To commence with the Numerical test cases (chap, x), it is 
shown in case i (p. 90) that selection would have great difficulty, 
as its very name suggests, in causing the evolution of vast and 
increasing numbers of plants, whilst under differentiation this is 
automatic, and follows the rule of the hollow curve. In case ii 


(p. 94) it is shown that while natural selection can make no 
predictions, under differentiation it is clear that on the average 
the size of the largest genus in the family must go with the size 
of the family itself, which proves to be the case, whilst in case iii 
(p. 95) the gap in size between first and second genera, second 
and third, and so on, is predicted as, and proves to be, a rapidly 
diminishing one. In case iv (p. 97) it is predicted, and proved, 
that the proportions of very small genera, considereti as relics 
under natural selection, must on the average be larger the larger 
the family, while it would be expected to be the reverse under 
selection. In case v (p. 99) it is shown that the hollow curve is 
entirely in favour of differentiation, and in case vi (p. 100) that 
"Size and Space", a corollary of Age and Area, is equally so. 
Case, VII (p. 100) refers to a paper by Yule and Willis (76), 
showing that "the manner in which evolution has unfolded itself 
has been relatively little affected by the various vital and other 
factors, these only causing deviations this way and that from the 
dominant plan", a conclusion which obviously does not harmo- 
nise with the action of natural selection. Case viii (p. 101) shows 
that while on the average the parent genus in small families has 
as many species as all the rest, more and more genera are required 
to halve the family when it grows larger. This could be predicted, 
and is against natural selection. The numerical tests are all clearly 
in favour of differentiation. 

Morphological tests are described in chap. xi. In the important 
case IX (p. 110), differences in generic rank are dealt with. 
Natural selection can make no predictions, and simply regards 
all genera as generic stages in evolution, and of rank as nearly 
the same as the systematist can compass. Differentiation, how- 
ever, says that the rank of a genus of a very small family will be 
approximately equal, on the principle of divergent mutation, to 
that of the sub-family of a large family. This proves to be the 
case, giving very strong evidence indeed for evolution by diver- 
gent mutation, and showing that the rank of a genus varies with 
its position, and the size of it and of its family. In case x (p. 114) 
the fact, hitherto almost totally ignored, is considered, that the 
characters of plants are generally shown in their perfect condi- 
tion, and especially so those of the higher groups. This could not 
happen under selection, to which 95 per cent or less of perfection 
would be as good as 100 per cent. This is a simple, but destructive 
argument against gradual acquisition of characters. In case xi 
(p. 115), the difficulty as to how natural selection got a grip upon 


the early stages of non-adaptive characters is considered, and it 
is pointed out that by differentiation there need not be such 
stages, nor is adaptation called in. In case xii (p. 118) is con- 
sidered the case of alternate and opposite leaves, a very common 
case of divergent characters with no transitions, and where it 
is almost impossible to suggest any adaptational value in the 
difference between them. Selectionists have to admit that 
anatomical needs are more potent than adaptational. This ques- 
tion of the relative value of characters has been somewhat 
ignored. In case xiii (p. 120) staminal characters are dealt with 
in the same way, and give similar evidence. In case xiv (p. 122), 
the berry is dealt with, and incidentally it is shown that there is 
little evidence of adaptation in this phenomenon, so often quoted 
as an illustration of it. Case xv (p. 124) deals primarily with 
achenes and follicles. Natural selection could not produce these 
in their perfect form, nor could it produce the perfect pod, and 
distinguish between this and the follicle in the marked way that 
one always finds. In cases xvi, xvii and xviii various other 
structural puzzles are considered, all much more easily explained 
by differentiation. In case xix (p. 129) the puzzle of correlated 
characters in so many of what are usually called adaptations is 
discussed, and it is shown that while it is quite inexplicable by 
natural selection, it is somewhat more easy with differentiation, 
which does not demand an adaptational value in everything. 
These (adaptation) correlations are useful, while most are not, 
but some day, perhaps, cytology will bring us the explanation of 
correlation phenomena. 

In chap. XII some further tests are considered under the head 
of Taxonomy, though largely a continuation of the last. The 
position of the largest genera of a family is dealt with in case xx 
(p. 134). On the theory of natural selection one can make no 
prediction about them, but on that of divergent mutation it is 
clear that in general they will be widely separated, inasmuch as 
they will have inherited their characters from the earliest muta- 
tions that took place in the family. This is just what proves in 
general to be the case, as is illustrated by the cases of the Ranun- 
culaceae and the sub-family Silenoideae, etc. In some cases, e.g. 
Clematis, the second largest genus in its family, the genus does 
not seem to have given rise to a sub-famih' inheriting its most 
obvious divergent character, the opposite leaves, but more usually 
this is the case, and one finds the large genera heading sub- 
families or other divisions. This is as predicted, whilst natural 


selection is quite helpless to explain it. Good evidence is thus 
given for differentiation. In case xxi (p. 136) the three largest 
families are shown to occur one in each of the three great divi- 
sions of the flowering plants ; this seems to indicate the proba- 
bility of very large mutations in very early divergences. In 
case XXII (p. 137) the mere fact that one can usually construct 
dichotomous keys goes to prove differentiation. In case xxiii 
the fact that divergence from the usual family characters is more 
pronounced the larger the family, goes the same way. In case xxiv 
(p. 138) the puzzling but frequent case of parallel variation in 
one, or in two or three related, families, very difficult to explain 
by selection, is simple to differentiation, whilst in case xxv 
(p. 140) widespread organisms are shown to be the simpler, 
though it does not say much for the advance in organisation 
supposed to be the result of selection. Darwin himself puts it 
down to their greater age, as does the writer. 

In chap. XIII a few tests based on Geographical distribution 
are given, but the full development of this attack upon the 
current theory of evolution must be left for the publication of a 
book which the writer has in preparation. In case xxvi (p. 146) 
the difficulties brought up by age and area are considered, 
especially the fact that on the average the distribution within a 
country goes with the distribution outside. As the conditions 
must vary, this goes to show that gradual adaptation other than 
physiological can have had little or nothing to do with the distri- 
bution. Natural selection has had to call in two supplementary 
hypotheses to explain the facts brought up about endemics and 
their distribution in Ceylon, and these hypotheses are mutually 
contradictory. The fact that the distribution of family surnames 
in Canton Vaud (p. 149) also matches that of plants, including 
endemics, goes to show that natural selection had very little to 
do with the latter other than purely locally. In case xxvii 
(p. 149) it is shown how contour maps may be constructed for 
most genera, especially when they are small, and have in the vast 
majority of cases only one centre. As no one genus takes any 
notice of the contours of any other (p. 154), the contours can 
hardly be determined by any local conditions. Great Britain, 
with its great variety of conditions, has nothing but margins of 
contours. In case xxviii (p. 154), already published, it is shown 
how the relationships of the smaller genera and of the species in 
a genus, in any given family, often show such great geographical 
divergence, with its near relatives separated by distances which 


may even be enormous, crossing the oceans, or even the equator. 
Natural selection could not explain this by any destruction of 
transitions, for the separations are of all sizes and in all directions. 
The only simple explanation so far proposed is that the local 
genera or species are due to direct mutations from the linking 
large and widely distributed genera or species that cover the 
places in which they occur. This of course involves the acceptance 
of differentiation. In case xxix (p. 156) it is showTi how variety 
in structure shows no necessary relation to variety in conditions, 
as one would expect under natural selection. In case xxx (p. 158) 
the difficulty is pointed out, of explaining, under natural selec- 
tion, a very common type of distribution. Many genera show one 
or more widely distributed species, usually very polymorphous, 
accompanied by local endemic species of the same genus in 
various parts of their range. The only simple explanation is that 
put forward by Guppy and by the writer that these endemics 
have been derived from the widely distributed species by one or 
more mutations. The incomprehensibility of selection is further 
developed in case xxxi (p. 161). Incasexxxii (p. 161) the incon- 
sistency of the contention that characters are less constant the 
less useful they are, is pointed out, and in case xxxiii (p. 162) the 
bearings of Hooker's discovery of the constancy of the numerical 
relation between Mono- and Di-cotyledons are pointed out, with 
the fact that there is no monocotyledonous mode of life. Case 
XXXIV treats of overlap of genera. 

It is clear that the tests give very strong evidence indeed in 
favour of the theory of differentiation or divergent mutation, 
according to which the course of evolution is in the opposite 
direction to what has hitherto been supposed, and by mutations 
which tend to diminish as time goes on, but go in the direction 
family — genus — species. The organism that first represents the 
family is, of course, at the same time its first genus and species, 
but these are of different rank from genera and species in a 
larger family. By further mutations this will then give rise to 
further genera and species. The first new genus formed will 
usually be widely divergent from the parent genus of the family, 
even if the family be quite small, e.g. of two genera only. Later 
formations will be less and less divergent on the whole, but will 
show some of the characters of divergence of their first parents. 
The main lines of divergence are therefore given by the latter, 
and later genera fill them in, as shown by a good dichotomous 
key. As time goes on, new genera will necessarily be evolved at a 
continually increasing rate, and each, given time enough, may 


ultimately become the parent, not only of many species, but of a 
group of generic offspring forming a sub-tribe or larger division. 
The whole family will at last end in the tail of genera containing 
one species each, as shown in the hollow curve. The oldest genera 
will have the most species, and the number will diminish as does 
the age, till we come to the tail of monospecific genera. 

There is thus very strong evidence to the effect that evolution 
has gone on without any direct reference to natural selection so 
far as we can at present see. The new form will appear, whether 
it be desirable, or suitable, or not, and whether it then survive 
will depend upon the action of natural selection, with reference 
to the conditions at the moment. The business of natural selec- 
tion is (1) to kill out everything in any way unsuitable to the 
conditions that surround it at the time, either at its first ap- 
pearance upon the scene, or when a change of conditions occurs ; 
and (2) to adjust to its surroundings, if possible, every new form 
that comes into the place, whether a new species just born, or a 
species newly arrived from somewhere else. There is thus plenty 
of occupation left for natural selection, and in a field where its 
usefulness and value have never been questioned. The early 
pioneer species will, of course, get the best chance, and as each 
newcomer arrives, increasingly close and careful adjustment will 
be needed, adjustment which natural selection will apply without 
fear or favour. 

Lastly, the evidence is equally strong that in the process of 
evolution, at any rate as a general rule, the new species formed 
(which might also be a new genus or even new family if the muta- 
tion were a little larger) would appear at one step by sudden 
mutation. Evolution goes on, but we can see no reason at present 
that will determine that it shall go in any particular direction, 
especially in one that shows greater adaptation. The mere fact of 
the survival of the "lower" forms in such numbers, like mosses, 
ferns, and liverworts, is against the idea, of any rapid progress in 
adaptation, but probably when an "adaptation" appears, such 
for example as climbing habit, it will be allowed or encouraged to 
survive, though why it should appear is at present a mystery. 

It is an inspiring thought that so great and complex a process 
as evolution must have been has not been a mere matter of 
chance, but has behind it what one may look upon as a great 
thought or principle that has resulted in its moving as an ordered 
whole, and working itself out upon a definite plan, as other 
branches of science have already been shown to do. Darwinism 
made the biological world a matter of chance. Differentiation, 


backed by the universal occurrence of the hollow curves, shows 
that there is a general law, probably electrical, at the back of it. 
And if evolution goes on without reference to adaptation values, 
each genus giving rise to another, and both surviving (as a rule), 
then the hollow curve becomes an integral part of it. Further 
refinements must be left to the mathematicians, and will doubt- 
less provide interesting results. 

Differentiation is not based upon adaptation at all, the 
latter remaining a primarily physiological phenomenon. The 
ordinary type of adaptation, that is familiar to agriculturists, 
is described in the following extract from a paper by Cockerell. 
" In California certain scale insects, subjected to poisonous fumes 
by the horticulturists, have, by a process of the survival of the 
fittest, developed resistant races, not distinguishable by any 
morphological characters." The writer was very troubled by 
cockroaches in his (tropical) house, and used a certain much- 
advertised poison, but though at first the death-rate was very 
high, presently there appeared a race of cockroaches that was 
immune, but looked exactly the same as their predecessors. "The 
chance of introducing from outside an all-round superior strain 
diminishes as the adaptation of the local strain to its environ- 
ment increases" (77, p. 283). Many similar extracts from agri- 
cultural papers might be quoted. 

There is good reason to suppose that in some way the genes 
and chromosomes are immediately responsible for the evolution 
that is going on. Their divisions and fusions strongly suggest some 
electrical process, with which the suggested action of cosmic rays 
may have something to do. Or again, something of the nature of 
genie changes may be going on, and occasionally result in the 
taking up of "more or less stable positions of equilibrium in cell 
division" as suggested by the writer in 1907. The apparently 
purposeless way in which distinguishing characters go together is 
verv like the similar behaviour seen in anv mutation involving 
more than one character. There is no evident reason, nor sugges- 
tion of reason, why a Monocotyledon should have at the same 
time one cotyledon, a trimerous flower, a parallel-veined leaf, and 
a peculiar anatomy. Nor why Cruciferae should have tetra- 
d}aiamous stamens, Dryas eight petals, and so on. Nothing but 
the direct effect of the genie composition, with heredity, will 
explain why the characters are shown in perfection. 

The continual appearance of characters with complex correla- 
tion that could not be due to selection, such as the characters of a 


family, genus, or other group, or such as climbing stems accom- 
panied by the means of climbing, goes to show that the family 
characters, or the climbing habit, must have been produced by 
some sudden chromosomic change, but by what, and how, deter- 
mined, we are as yet completely ignorant. Many other "adapta- 
tions" come into the same categforv. 

A very probable large mutation, giving the ancestor of what is 
now a large genus, is that which perhaps gave rise to the colum- 
bine (Aquilegia), which can easily be imagined as arising from the 
larkspur (Deljjhinium) by a mutation like that which often gives 
a symmetrical sport in the toad-flax flower. 

It would seem probable that the early future development of the 
study of evolution will be largely based upon the study of cytology, 
for it would seem that the conception of gradual adaptation, at 
any rate in its present form, must be abandoned. The larger 
groups seem to have appeared before the smaller, upon the whole, 
the force or size (if one may use such a term) of the mutations 
that went on diminishing as time went on, the number of smaller 
mutations on the whole increasing in proportion to the larger. 
What actual part the external conditions took in the matter 
is at present inexplicable, but there is nothing in the structural 
characters, as a general rule, to show that the part was a large one. 

One must not lose sight of the hybridisation that is so easily 
possible, and of which Lotsy (27) made so important a feature in 
evolution. At the same time, if mutation can take place, as 
seems highly probable, in such a way as to cross the "sterility 
line" between species, and so to isolate them, it does not seem 
very likely that fertile species -hybrids will be produced in such 
numbers as to have an important influence upon evolution 
generally, though one must not forget the possible influence 
of the cosmic rays or other factors in causing the doubling of the 
chromosome numbers. Hybridisation seems very unlikely among 
the widely separated genera that seem to be the firstcomers, in 
most, if not in all, families, but as one goes down the scale, one 
seems to come among genera that are closer and closer together 
in their taxonomic characters, and with these hvbridisation 
would seem to become more and more possible, and more likely 
to occur. Still more would this be the case among the species, 
and here again rather in the species of large genera. It seems to 
the writer that this question of hybridisation, with its increasing 
possibilities in the genera and species of later formation, may be 
one of some importance, though one must, of course, not forget 


that these later genera and species will be of much less wide 
distribution than the earlier. 

The conceptions thus put forward have several possibly even 
unexpected bearings. If new species and genera can thus arise in 
widely separated places, though related, there seems no reason 
why the same character, produced of course by some particular 
arrangement of genes or chromosomes, should not at times arise 
from ancestors in which it did not itself occur, i.e. should arise 
polyphyletically, or from different ancestors. One may even 
imagine more than one character arising in this way, so as to 
form, though probably only with great rarity, a polyphyletic 
genus. In some such way as this one may imagine the case of one 
genus coming through another, as suggested by Bower in the 
ferns (2). One must remember, too, that what look like species 
of the same genus and closely allied, need not necessarily be such, 
and one must compare their chromosome numbers. It is even 
possible that originally separate types may converge until they 
may be able to become cross-fertilised. 

The sudden appearance of similar mutations at widely separated 
places may be easily accounted for by a similar construction in 
the chromosomes of their ancestors, which might give rise to 
similar mutations. There is no definite reason that one can see — 
though, of course, this is unfamiliar ground to the writer — why 
the same genie distribution should not appear in two new species 
formed from one genus, thus giving rise to a new genus of two 
species, and possibly even discontinuous in distribution. 

Finally, a very strong argument in favour of differentiation, 
just as with Age and Area, is that by its aid one may make a 
great many predictions as to what will be found to occur, and 
find that these predictions are borne out by the facts. A number 
of such are to be found in many of the test cases given in 
chaps, x-xiii, and others may be found elsewhere. Now upon 
the theory of natural selection it is as a rule impossible to make 
any predictions at all, and when, as for example in several test 
cases, one may venture a prediction, this is found to be opposed 
to that made upon the theory of differentiation, and is not borne 
out by the facts, which always favour the latter theory. This seems 
to the writer to be a very strong argument in favour of differentia- 
tion or divergent mutation. At first, owing to the fact that one 
has to think, so to speak, in the reverse direction from that to 
which one has been accustomed (i.e. from family to variety, not 
from variety to family), it is not always easy, but one soon gets 
into the new direction of thought. 



1. The world has undoubtedly been peopled by an evolution of 
forms one from another, giving rise, as time has passed, to beings 
of increasing complexity. 

2. The process of evolution appears not to be a matter of 
natural selection of chance variations of adaptational value. 
Rather it is working upon some definite law that we do not yet 
comprehend. The law probably began its operations with the 
commencement of life, and it is carrying this on according to 
some definite plan. 

3. Evolution and natural selection are probably to a great 
extent independent, and they work at right angles to one another, 
with (in plants at any rate) little mutual interference. 

4. Evolution most probably goes on by definite single muta- 
tions, which cause structural alterations, which mav, but bv no 
means necessarilv must, have some functional advantao^e at- 
tached. If such an advantage appear in the mutation, natural 
selection will likely allow it to survive. There is no necessary 
reason why the immediate ancestor should die out. 

5. Evolution goes on in what one may call the downward 
direction from family to variety, not in the upward, required by 
the theory of natural selection. 

6. Evolution thus moved in the opposite direction to that 
required by natural selection, and thirty-four test cases are 
given, all giving evidence to that effect. 

7. Evolution is no longer a matter of chance, but of law. It 
has no need of any support from natural selection. 

8. It thus comes into line with other sciences which have a 
mathematical basis. 

9. The theory of natural selection has been trying to work it 

10. Mutation tends to be divergent, especially in the early 
stages of a family. The family, consisting probably of one genus 
and one species, is probably first created by a single mutation, 
whilst later ones are usually less marked than the first, and give 
rise to further genera and species. The earliest mutations ulti- 
mately give rise to the chief divisions of the family. 

11. The Linnean species is not necessarily a conglomeration of 
forms made from below upwards, but is rather a stage on the way 
downwards to the Jordanian species. 


12. Varieties are the last stages in the mutation, and are not, 
as a rule, incipient species. 

13. Chromosome alterations are probably largely responsible 
for the mutations that go on. 

14. The theory of natural selection is no longer getting us any- 
where, except in politics (influence of the dead hand). 

15. It comes in principally as an agent to fit into their places 
in the local economy of the place where they are trying to grow, 
the forms there furnished to it, whether newly evolved, or only 
newly arrived, killing out those in any way unsuitable. 

16. It has, therefore, not been responsible for the progress that 
has been made by the actual evolution of new forms, but it has 
been all-important in fitting them into their places in the economy, 
which is always increasing in complexity. 

17. The theory of natural selection makes evolution a con- 
tinuous and gradual process, diff'erentiation a discontinuous one. 

18. Natural selection (the struggle for existence) works rather 
upon individuals than on groups. It causes the survival of the 
fittest population, rather than the fittest type in the mixture. 

19. It can make few or no predictions, while diff'erentiation, 
like age and area, can make many, which are usually successful. 

20. Adaptation has been mainly internal or functional, rather 
than external or structural. 

21. Differences in structure do not necessarily mean difiPerences 
in adaptation. 

22. The mutations supposed in diff'erentiation would at one 
step cross the "sterility line" between species, which has always 
been a great stumbling block to natural selection; and thus at 
once isolate the new form, preventing its loss by crossing. 

23. Diff'erentiation makes it possible for evolution to go on 
more rapidly than under natural selection. 

24. It explains the great discontinuity seen in the facts of 
economic botany. 

25. It explains the difficulty, almost insuperable to the theory 
of natural selection, of the increasing divergences of characters 
as one goes up the scale from species to family. 

26. It gets over the difficulty of early stages, and of the fre- 
quent correlation of characters, and the need of calling in "mor- 
phological necessity"; it does not need to call in adaptation, as 
the theory of natural selection has to do ; and it explains why the 
large genera are the most variable. 

27. It explains the fact that adaptation is so often generic. 


28. With its probably genetical basis, it explains the difficulty 
of the perfect form in which characters, and especially those of 
the higher divisions, are exhibited, which was almost impossible 
to the theory of natural selection. 

29. It gets over the difficulty caused by the fact that few tran- 
sition stages are found, either in living or in fossil plants. 

30. It explains the universal hollow curve, as well as age and 
area and size and space, all impossible to the theory of natural 

And one may add : 

The 34 test cases given often bring out new and sometimes 
unexpected relations, e.g. the grouping of a family (or sub-families 
if large) into large, medium, and small genera. 

Adaptation, isolation, and other phenomena are discussed from 
somewhat new points of view. 

Upon pp. 76, 139, and elsewhere, indications have been given, 
more or less unintentionally, about things that will only appear 
in a forthcoming book upon geographical distribution. Therein 
the writer hopes to show that the adoption of age and area and 
of differential or divergent mutation, for both of which good 
proof has now been given, reduces the problems of distribution 
to a simpler form. By abandoning the supposition, necessarily 
inherent in natural selection, that plants may be divided into 
successes and failures, the one expanding and the other contract- 
ing the area occupied, all may be regarded as behaving in much 
the same way as their near relatives. One thus obtains a more 
satisfactory picture of how evolution and geographical distribu- 
tion went on, and how thev fitted into one another. 

WED 13 



The list is made up from the key at the end of my Dictionary, and 
includes the necessary characters to distinguish one family from 
another. They are arranged as far as possible in divergent pairs, 
and it will at once be noticed that most of them do not lend 
themselves to possessing intermediates or transitions. 

Herbs, shrubs, trees; parasites, saprophytes, epiphytes, thalloid. 

Roots from tap-root, or adventitious. 

Stem, rhizome, bulb, etc.; creeping, climbing, or not; herbaceous 
or woody; jointed or not; mono- or sympodial; angled or not; 
with latex or resin, or not. 

Leaves radical or cauline ; alternate, opposite, or whorled ; in two 
ranks, or in three or more; sheathing or not; ligulate or not. 

Leaves simple or compound ; palmate or pinnate, etc. ; entire or 
lobed or toothed ; fleshy or hairy or not ; pitchers or not ; with 
oil cavities, glandular dots, with chalk glands, or not. 

Leaves stipulate or exstipulate; parallel- or net-veined; dorsi- 
ventral or isobilateral ; asymmetrical or not. 

Inflorescence racemose, cymose, or mixed; ^ or unisexual; a 
raceme, corymb, catkin, mono- or dichasial cyme, etc. etc.; 
with bracts or not; with spathe or not; with bracteoles or not. 

Receptacle convex, flat, or hollow; with or without effigurations. 

Involucre or none; epicalyx or none; disc or not. 

Flower spiral or cyclic; ^ or ^ $; mon- or dioecious; with 
perianth or not; homo- or hetero-chlamydeous ; iso- or hetero- 
merous; with parts in twos, threes, fours, etc. 

Flower regular or zygomorphic; zygomorphism vertical, trans- 
verse, or oblique; with ray florets or not; heterostyled or not; 
resupinate or not. 

Perianth petaloid or sepaloid, or none. 

Calyx whorled or spiral; convolute, imbricate, or valvate; poly- 
or gamosepalous ; odd sepal anterior or posterior. 


Corolla of free or united petals; regular or two-lipped; convolute, 
valvate or imbricate; alternate with sepals, or superposed; 
corona present or not. 

Androphore, gynophore, column, etc., or not. 

Stamens in one, two, or more whorls, or spiral; staminodes or not; 
epipetalous or not; on disc or not; changed to nectaries, etc., or 

Stamens in one, two, or more whorls ; in one whorl all present, or 
not ; spiral and oo or not ; free, or united in tube or in bundles ; 
diplostemonous or obdiplostemonous ; antepetalous (if one 
whorl) or not; epipetalous or not; on the disc or not. 

Stamens branched or not; tetra- or di-dynamous, or not; odd 
stamen anterior or posterior; staminodes or not; changed to 
nectaries or not; exploding or not; bent inward in bud, or not. 

Anthers dorsi- or basi-fixed, or versatile; extrorse or introrse; 
mono- or di-thecous; opening by splits, valves, pores, teeth, 
etc. ; connective with or without appendages. 

Pollen spherical, polyhedral, etc.; smooth, prickly, warty, etc.; 
in tetrads, pollinia, etc. 

Ovary superior or inferior, etc.; 1-2-3-4-5-more carpels; 1-2-3-4-5- 
more loculi. 

Carpels spiral or in whorls; apo- or syn-carpous; united only by 
style; 1-2-3-more; transverse or anteroposterior to flower; 
some abortive, or not ; in superposed whorls or not. 

Placenta parietal, axile, basal, apical, free-central, etc. ; bilobed. 

Ovules 1-2-few-many per loculus; in one, two, or more rows as 
seen in transverse section; stalked or sessile; erect, horizontal, 
or pendulous; orthotropous, anatropous, campylotropous ; on 

Raphe ventral or dorsal; micropyle up or down. 

Style basal or terminal ; present or not, one, or as many or twice 
as many as carpels; entire or divided; with pollen-cup. 

Stigma capitate, lobed, divided, etc.; petaloid or not; sessile or 

Fruit fleshy or dry; achene, follicle, siliqua, schizocarp, capsule 
(loculi-septi-cidal, septifragal, etc.), drupe, berry, etc., etc.; 
dehiscent or indehiscent, etc.; simple or compound; winged or 
not; with pappus, or hooks, etc. 



Replum or not; individual carpels divided by horizontal or 
longitudinal walls, or not. 

Seeds per flower, or per carpel 1-2 -few-many; albuminous or 
exalbuminous ; with endo- or perisperm; with aril or not, 
winged or not; hairy or not. 

Embryo with one cotyledon or with two ; large or small in propor- 
tion to endosperm; straight, curved, twisted, folded, etc. 

Endosperm oily, starchy, fleshy, cartilaginous, etc. ; ruminate or 



Vegetative organs 

Land plants — waterplants 

Roots — none 

Green plants — parasites 

Climbing — not 

Shrubby — annual 

Shrubby — undershrub or herb 

Leaves cauline — radical 

Leaves 2-ranked — not 

Leaves opposite — usually alternate 

Leaves opposite, stipulate — alternate, 

Leaves palmate — simple or pinnate 

Leaf-thorns in axil — not 

Cystoliths — none 

Glandular or stinging hairs — none 

Hairs simple or none — usually branched 




Lardizabalaceae, Polemoniaceae 




Iridaceae, Zingiberaceae 

Gentianaceae, Myrtaceae 


Bombacaceae, Datiscaceae, Lar- 
Loganiaceae, Urticaceae 


Free or slightly united — long tube 
Broadly campanulate — salver-shaped 
Valvate or other aestivation 

Spurred or not 
Labellum — none 

Petals with appendages — without 
Petals outside disc — on margin 
Honey-leaves — none 
Lateral teeth of corolla overlap — 

Dichapetalaceae, Tamaricaceae 

Ebenaceae, Elaeocarpaceae, Gen- 
Papaveraceae, Violaceae 

Fruit and Seed 

Berry or drupe — dry fruit 

Other varieties of, or variations in, 

Bromeliaceae, Commelinaceae, Fla- 
gellariaceae, Myrtaceae, Oxali- 
daceae, Pittosporaceae, Rhizo- 
phoraceae, Ulmaceae, Zygophyl- 

Connaraceae, Epacridaceae, Faga- 
ceae, Geraniaceae, Labiatae, 
Malpighiaceae, Oleaceae, Pole- 
moniaceae, Proteaceae, Ranun- 
culaceae, Valerianaceae, Vochy- 



Embryo straight — curved, or otherwise 
differently shaped 

Endosperm — none 

Endosperm ruminate — not 
Seeds basal— not 
Seeds embedded in placenta — not 
Seeds in one plane — in more than one 
Capsule many-seeded — one-seeded in- 

Basellaceae, Butomaceae, Cheno- 
podiaceae, Convolvnlaceae, Eu- 
phorbiaceae, Droseraceae, Her- 
nandiaceae, Melastomaceae, Sol- 
anaceae, Ulmaceae 

Goodeniaceae, Myrsinaceae, Nym- 
phaeaceae, Ochnaceae, Rhizo- 






These will serve as examples of the degree of divergence of the 
characters that separate the sub-families or tribes of the various 
families, without going into too great detail. 



Wing on fruit unilateral 
P 5, bracteoles 



G (2), style slender, 2- 

Capsule elastic. Ovules 
pendulous one above 

Embryo spiral with nar- 
row cots. 

K and C alternate. A free Caricaceae 


Leaves opposite. Plumule 
thick and straight 

Sepals with distinct midrib 

Leaves opposite 

K in tube. Disc normal 

P of ^5-8. 0\nile basal. ? 
flowers in groups of 4 



Sta. in one whorl. Ovules Hydnoraceae 

Ovary 1-locular 
C valvate. A 15-30 

Disc of few teeth. Sta. few. 
Bracts entire 

Pets. 6-7. Sta. unequally 
long, anthers by longi- 
tudinal slits 

Bracteoles. (C). Pollen 
spiny. Perennial 


L. opp. C 5, very unequal, 
one spurred. A to 10 

Partial fruit not winged 

Stamens not more than 6 
C. 3 stds. G 1-loc. with 
basal or parietal placenta 










Wing all round the fruit 
P 4, exc. term, flower. No 

G (3), style thick, 3-armed, 

arms bifid 
Berry. Ovules pendulous 

side by side 

Embryo curved with broad 

K and C superposed. A 

Leaves alternate. Plumule 

long and spiral 
Sepals with no midrib 
Leaves alternate 
K free. Disc excentric 
P of cJ usually 4. Ovule 

lateral. $ flowers in 

groups of 3 
Two whorls. 0\ailes sunk 

in placenta 

Ovary 6-10-locular 
C convolute. A oo 

Disc hollow. Sta. oo. 

Bracts divided 
Pets. 3. Sta. equally long, 

anthers by apical slits 

No bracteoles. C. Pollen 

smooth. Annual 
L. alt. C 3, alike. A 3-5 

Partial fruit with 3 broad 

Stamens more than 6 
(C). No stds. G3-10C. with 

axile placenta 


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63. Relative Age of Endemic Species. Ann. Bot. xxxi, 1917, 

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64. The sources and distribution of the New Zealand flora. 

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(r.C. = Test Case) 

Achenes, T.C. xv, 124 

Acrotrema, 50 

Adam's Peak, endemics, 61 

Adaptability, 60, 145 

Adaptation, 4, 13, 14, 15, 23, 39, chap. 
VI, 52, 131, 146, 170, 176, 188; 
generic, 18, 60, 107 ; geographical 
distribution based on, by selec- 
tionists, 56; gradual, 108, 117, 
1 65 ; importance exaggerated,68 : 
internal, 15, 44, 57, 58, 116; in 
Podostemaceae, 18 ; in structural 
characters, 4, 44, 52, 116; phy- 
siological, 15 ; structural charac- 
ters of adaptational value, 52-3 ; 
to movable conditions, 56 

Age and Area, 27, 29, 30, 31, 69, 86, 
140, 146, T.C. XXVI, 146; com- 
parison with allies, 29; essence 
of theory, 69, 95 ; gradual devel- 
opment, 27, 29; opposition, 30, 

Alternate and opposite leaves, T.C. 
XII, 118 

Anaphalis, 26 

Anemone, 105; in India, 159 

Animals, 136 

Aquilegia, 49, 189 

Artocarpus, 31, 148 

Assumptions of Natural Selection, 
see Natural Selection 

Author's change of ^^ews, 18-20, 24, 
26, 39, 44, 46, 67, 171-2 

Axioms of taxonomy, 132 

Balkan endemics, 63 

Barriers to spread, 59, 69, 153, 

Bateson, W., 164 
Berry fruit, T.C. xiv, 122 
Beta, contour map of, 153 
Bog plants, 53 
Breeding, 10, 56 

Cardamine, distribution, 155 
Carludovica, 76 
Caryophyllaceae, 96, 108, 124 
Ceanothus, 31, 147 
Centrolepidaceae, 49, 139 

Ceylon, 18, 27, 33, 39, 50, 59, 61, 146, 

Chandler, Miss, 64, 72 
Change of conditions, 55, 146 
Change of views, see Author 
Characters, differences in, 16; early 
stages, T.C. xi, 115: easy of 
acquisition, 139, 140; famUy, 
16, 74, 76, 106, 108, 180; more 
constant the more useful (?), 
T.C. XXXI, 161 ; of distinction of 
families, genera and species, 
106 ; value of, 71 
Chemistry of plants, 8 
Chromosomes and evolution, 188 
Classification, 1, 2 
Clematis, 70, 135; in India, 159 
Climatic conditions, differentiation, 

Climbing plants, 57 
Colem, 24, 132, 166 
Common names, 2 
Compositae, 48, 98, 102 
Conditions of life, 3; equal, with 
great structural difference, 44; 
variation in, 91 
Continuous variation, 10 
Contour maps, T.C. xxvii, 149 
Convergence of evolution, 135, 190 
Correlation, 11, 48, 57, 58, T.C. xix, 

129, 188 
Cosmic rays, 26, 62, 63, 115 
Cruciferae, 154; distribution, 155 
Cvclanthaceae, 76 
Cytology, 89, 189 

Darwin, Charles, 3, 65, 74, 91, 110, 

Darwin, Sir Francis, 9, 18 
Darwinism and its difficulties, 6, 10, 

13, 21, 30, 39, 48, 115, 117, 139, 

164, 166, 167, 187 
Dead hand, influence of, 6, 144 
Death of species, 72 
Delphinium, 49, 189 
Destruction under natural selection, 

144, 155 
Dianthus, 86 
Dicotyledons, 15, 43, 47 



Differences in character, 16 

Differences in generic rank, T.C. ix, 

Differentiation, 6, 17, 39, 46, 50, 88, 
96, 112, 181, 186, 187, and chap. 
VIII, 65 ; author's pubhcation of, 
68; course of evolution under, 
68, 69; diagram of process, 69, 
70, 111; direction the oppo- 
site to selection, 68; generic 
rank under, T.C. ix, 110; 
growth of family under, 71 ; 
Guppy's publication of, 66; 
Hooker on, 74; in Ranuncula- 
ceae, 81; in Silenoideae, 86; of 
climate, 59; survival of parent 
under, 66; and see Test Cases, 
chaps, x-xiii 

Dilleniaceae, distribution, 44, 45 

Dipterocarpaceae, 125 

Discontinuity in evolution, 8, 169 

Dispersal mechanisms, 123 

Distribution, 21 ; and age, 29, and 
cf. Age and Area; barriers to, 
59, 153; discontinuity, 5; not 
determined by selection, 39 

Divergence of character, 74, 119,138, 

Divergence of variation, 16, 82, 85, 
112, 137, chap, ix, 74 ; increasing 
upwards, 76, 113; more or less 
equal at corresponding levels in 
large, medium, and small fami- 
lies, 112 

Droseraceae, 126 

Dry and wet zones, 59 

Early stages of characters, T.C. xi, 

Ecology, 9 

Economic botany, 8, 89, 169, 177 

Endemics, as young beginners. 30, 
154, 160; in large genera, 26; in 
North America, 30; local adap- 
tation, 30, 147 ; may prove very 
useful, 89; not usually mori- 
bund, 28; of Balkans, 63; of 
Ceylon mountains, 26, 61 ; of 
New Zealand, 29 ; often Linnean 
species, 49; relics, 30 

Endemism, 24, 26, 27, 30; on 
mountains, 26, 61 

Englishman, acclimatisation of, 105 

Eriocaulaceae, 49, 139 

Eugenia, 26 

Euphorbia, distribution, 155 
Evolution, 3, 21, 22, 41, 46, 50, 51, 
65, 66-9, 89, 95, 100, 117, 175, 
187, etc. ; at right angles to 
natural selection, 117, 175, 187; 
backwards, 22, 32, 65, 66, 68, 
88, 98, 175; course under Dif- 
ferentiation, 68, 69; de luxe, 21; 
direction of movement, 67, 182 ; 
downwards, 46, 65 ; in structural 
characters, 4; mechanism of, 41, 
89; must go on, 21 ; no longer a 
direct expression of improving 
adaptation, 95 ; not a matter of 
chance, 187; nothing to do with 
adaptation, 41 ; on mathemati- 
cal lines, 50, 175, 178; plan, 51 ; 
statistics, 50, 100; survival of 
parent, 66; two theories dia- 
metrically opposed, 89 ; and see 
Test Cases, chaps, x-xiii 
Extermination under natural selec- 
tion, 69, 155; of parent, 4, 13, 46, 
167, 173 

Families, ditype, 78; monotype, 79 
Family characters, 16, 106, 108, 143, 

Follicles, T.C. xv, 124 
Fossils, 12, 72 
Frequency distribution, 10 
Fungi, 21, 158 

Gaps between larger genera in a 

family, 97 
Gene change with separation, 62 
Genera, relative sizes, T.C. iii, 95 
Generic adaptation, 18, 59, 107, 126, 

Geographical distribution, 9, 24, 26, 
39, Test Cases, 142; based on 
adaptation by selection, 56, 68, 
Geographical localisation of struc- 
tural features, 123 
Geological catastrophes, 73 
Guppy, H. B., 16, 39, 66, 68, 74, 89, 
132, 174, 175, 186 

Halving of species in a family, T.C. 

VIII, 101 
Harland, S. C, 62 
Hedyotis, 26 
Hollow curve, chap, iv, 33; T.C. v, 

99; 164, 173 



Hooker, Sir J. D., 9, 17, 47, 74 
Huxley, T. H., 17, 74 
Hybrid formation, 143, 189 
Hydrocotyle, 58, 104, 145 
Hydrophytes, 52 

Increase in number with evolution, 

T.C. I, 90 
India, distribution in, T.C. xxx, 158 
Infinitesimal variation, 10 
Intermediates, 12, 16, 44 
Island floras, 62 
Isolation, 25, 26, 27, chap, vii, 61 

Jeans, Sir James, 90, 175 

Jenkin's criticism of Darwin, 5, 13, 

25, 165 
Jordanian species, 133 

Keys to families, 77, 85, 137 

Large families, position of, 136; 
larger the family, the larger the 
variety of conditions, 129 

Large genera, 17, 26, 80, 93, 94, 97, 
126, 134, 136, 163; among en- 
demics, 26 ; divergent, 136 ; gaps 
between, 97; origin, T.C. xvi, 
126; position of, T.C. ii, 94; 
successes, by selection, 93, 161 ; 
supposed to be best adapted, 17 

Likenesses of organisms, 1, 2 

Limit to life of species, 72 

Linking genera, 19, 155 

Linnean species, 61, 132, 166, 171 

Local adaptation of endemics, 147; 
conditions have small effect, 55 

Localisation of higher types, T.C. 
XXV, 140 

Lofgren, A., 62 

Logarithmic curves, 35, 174, fig. on 37 

Malthus, T. R., 3, 110 

Mechanism of evolution, 41, 89 

Menispermaceae, 152, and fig. 10 

Mesophyt€s, 52 

Mivart,'St G., 7 

MolUnedia, 33 

Monimiaceae, 33, 92, 136 

Monocotyledons, 15, 43, 47, 130; 
monocotyledonous mode of life, 
15, 45, 47, 162 ; relation to Dico- 
tyledons, 162 

Moors, plants of, 44 

Morphological test cases, 103 

Musk, loss of smell by, 66, 72, 111 
Mutation, 13, 20, 25, 41, chap, v, 43, 
48, 59, 63, 89, 115, 129, 170, 172, 
187, 189; differentiating, irre- 
versible, hereditary, 43; large, 
not seen, 48, 89; single, 59, 67, 
172; smaU, 59 

Natural Selection, 4, 5, 6, 13, 14, 15, 
21, 22, 24, 25, 41, 45, 54, 57, 58, 
69, 77, 78, 90, 97, 103, 106, 107, 
109, 110, 114, 115, 117, 139, 153, 
155, 166, 175, 177, 181, 187; 
adaptation by, 54 ; assumptions 
of, 4, 13, 54, 55, 107, 109, and 
especially 167; destruction 
under, 69, 155; difficulties, 10, 
21, 30, 39, 48, 58, 77, 78, 115, 
117, 139, 166; fascination, 103; 
individual, 15, 110, 177, 179; no 
room for operation, 25 ; not the 
driving force of evolution, 177; 
results in survival of fittest 
population, not type, 166; work 
too complex, 57 

Nature red in tooth and claw, 6, 110 

Nepenthes, 140 

New Zealand, contours and condi- 
tions, 154; distribution of en- 
demics and wides, 29; propor- 
tion Monocotyledons to Di- 
cotyledons, 162 

Opening of anther, 121 
Origin of plants and animals, 2 
Origin of Species, 3, 8 
Overhead force acting, 20 
Owen, Sir Richard, 7 

Paeonia, 84 

Parallel variation, 138 

Parasites, 130 

Parent and child, 50, 156 

Perfection of characters, 45, T.C. x, 

114, 178, 179-80 
Pinnate leaf, distribution of, 105 
Podostemaceae, 18, 19, 63, 141, 156 
Polyalthia, 50 
Polyphyly, 190 
Portulaca in India, 159 
Prediction, 89, 94, 97, 147, 190 
Pure stand, 91, 125 
Pyrenacantha, 130 

Rafflesiaceae, 21 



Range large, structural difference 

sometimes small, 44 
Rank and Range, 100 
Ranunculaceae, analysis of, 81, 135 
Ranunculus^ 50, 70, 135, 150, 151, 

and fig. 9 
Regression, 10 
Relative rank of genus and species, 

68, 113; sizes of genera, T.C. 

Ill, 95; value of characters, 119 
Relics, 4, 17, 26, 30, 31, 61, 79, 81, 

91, 93, 95, 113, 128, 132, 147, 

160, 173 
Restionaceae, 49, 139 
Rhipsalis (endemic), 62 
Ritigala, 24 
Rubiaceae, unusual characters, 118, 


St Hilaire, G., 65 

Sedum, 54 

Senecio, 126 

Silene, 86 

Silenoideae, 86, 136 

Single steps to genus or species, 59, 
117, 172, 187 

Siparuna, 33, fig. 1, 34, 63 

Size and Space, T.C. vi, 100 

SmaU, J., 72 

SmaD genera, failures (by natural se- 
lection), 93 ; proportion in famil- 
ies, T.C. IV, 97; satellites round 
large, 81, 128, T.C. xviii, 128 

Social legislation, 110 

Solanum, 138 

Special creation, 2, 164 

Species assumed to fight as units, 
107, 142, 144, 166, 179; formed 
at one step, 20 

Specific characters, 11, 109, 180 

Staminal characters, T.C. xiii, 120 

Statistics of continents, etc., very 
uniform, 172 

Sterility line, 12, 46, 143, 174, 189 

Stewart, C. Balfour, 47, 182 

Stratiotes, 64, 111 

Strobilanthes, 26 

Structural characters, 4, 8, 15, 44, 
52, 103; no necessary adapta- 
tional value, 109, 115; nothing 
to do with Ufe, 54 

Structural considerations override 
adaptational, 110, 115, 120, 
121, 129; difficulties for natural 
selection, 127 

Struggle for existence, 1, 3, 5, 22, 39, 

49, 54, 106, 110 
Styracaceae, 108, 161 
Successful species, 24; genera and 

species, 132 
Super-plants 90 

Surname distribution, 35, 39, 40, 99 
Survival of the fittest, 165 

Taxonomic axioms, 132; resem- 
blances of geographically widely 
separated plants, T.C. xxviii, 
154; tests, 132 

Tendencies, 120, 124, 138 

Test Cases between the rival theories 
(reviewed on p. 182): 

I. Increase in Number with Evo- 
lution, 90 

II. Size of the Largest Genus in a 
Family, 94 

III. Relative Sizes of Genera, 95 

IV. Proportions of Small Genera 
in Families, 97 

V. The HoUow Curve, 99 

VI. Size and Space, 100 

VII. Some Statistics of Evolution 
and Distribution, 100 

VIII. The Halving of the Species 
in a Family, 101 

IX. Differences in Generic Rank,l 10 

X. ThePerfectionofCharacters,114 

XI. The Early Stages of Cha- 
racters, 115 

XII. Alternate or Opposite 
Leaves, 118 

XIII. Staminal Characters, 120 

XIV. The Berrv Fruit, 122 

XV. Achenes and Follicles, 124 

XVI. The Origin of Large Genera, 

XVII. Some ^Morphological 
Puzzles, 126 

XVIII. The SmaU Genera, 128 

XIX. Correlated Characters, 129 

XX. The Position of the Largest 
Genera in a Family, 134 

XXI. The Position of the Large 
Families, 136 

XXII. Divergence of Variation. 
Systematic Keys, 137 

XXIII. Divergence from usual 
Family Characters, 138 

XXIV. Parallel Variation, 138 

XXV. Greater Localisation of 
Higher Types, 140 



Test Cases (cont.) 

XXVI. Age and Area, 146 

XXVII. Contour Maps, 149 

XXVIII. Taxonomic Resem- 
blances of (Geographically) 
widely Separated Plants, 154 

XXIX. Variety of Character with 
Uniform Conditions, 156 

XXX. A common Type of Distri- 
bution in India and Elsewhere, 

XXXI. Large (ienera the Most 
"Successful", 161 

XXXII. Characters the More 
Constant the More Useful, 161 

XXXIII. Relation of Monoco- 
tyledons to Dicotyledons, 162 

XXXIV. Overlap of Largest Ge- 
nera in a Family, 163 

Tetracera, 45 
Thalictrum, 104 
Transitions, 12, 16, 44, 

Trimen, H., 18, 24 
Tristichaceae, 21 

Tropical Forest, 22 
TurrUl, W. B., 63 

Umbelliferae, 154 
Unsuccessful genera, 128 

Variation, differentiating, 11, 14; 
inherited, 11; in sudden steps, 
10; irreversible, 11, 14; of 
character with uniform condi- 
tions, T.C. XXIX, 156 

Vaud, names in, 35, 40 (fig. 6), 148, 

Vries, H. de, 14, 170 

Wallace, A. R., 3 
Weather effects, 55 
Went, F. A. F. C, 104 
Willisia, 19 
Woolf, L. S., 6, 144 

74, 125, Xerophytes, 52 

Yule, G. Udny, 50, 90, 93, 100, 155,