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THE METHODS AND SCOPE

OF

GENETICS

fN INAUGURAL LECTURE DELIVERED
23 OCTOBER 1908

by
W. BATESON, M.A., F.R.S.

PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF CAMBRIDGE

Cambridge University Press
Fetter Lane, E.G. 4

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THE METHODS AND SCOPE

OF

GENETICS

11

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THE METHODS AND SCOPE

OF

GENETICS

AN INAUGURAL LECrURE DELIVERED
23 OCTOBER 1908

by
W. BATESON, M.A., F.R.S.

PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF CAMBRIDGE

Cambridge :

at the University Press

1912

}I

B»m »

First Edition 1908
Reprinted 191 2

PREFATORY NOTE

rjlHE Professorship of Biology was founded
in 1908 for a period of five years partly
by the generosity of an anonymous bene-
factor, and partly by the University of
Cambridge. The object of the endowment
was the promotion of inquiries into the
physiology of Heredity and Variation, a
study now spoken of as Genetics.

It is now recognized that the progress of
such inquiries will chiefly be accomplished
by the application of experimental methods,
especially those which Mendel's discovery
has suggested. The purpose of this in-
augural lecture is to describe the outlook
over this field of research in a manner
intelligible to students of other parts of
knowledge.

W. B.

28 October, 1908

-y

THE METHODS AND SCOPE OF
GENETICS

The opportunity of addressing fellow-
students pursuing lines of inquiry other than
his own falls seldom to a scientific man. One
of these rare opportunities is offered by the
constitution of the Professorship to which
I have had the honom- to be called. That
Professorship, though bearing the compre-
hensive title 'of Biology," is founded with
the understanding that the holder shall apply
himself to a particular class of physiological
problems, the study of which is denoted by
the term Genetics. The term is new; and
though the problems are among the oldest
which have vexed the human mind, the modes
by which they may be successfully attacked

THE METHODS AND

are also of modern invention. There is there-
fore a certain fitness in the employment of
this occasion for the deliverance of a discourse
explaining something of the aims of Genetics
and of the methods by which we trust they
may be reached.

You will be aware that the claims put
forward in the name of Genetics are high,
but I trust to be able to show you that they
are not high without reason. It is the
ambition of every one who in youth devotes
himself to the search for natural truth, that
his work may be fouud somewhere in the main
stream of progress. So long only as he keeps
something of the limitless hope with which
his voyage of discovery began, will his courage
and his spirit last. The moment we most
dread is one in which it may appear that,
after all, our effort has been spent in explor-
ing some petty tributary, or worse, a back-
water of the great current. It is because

SCOPE OF GENETICS

Genetic research is still pushing forward in
the central undifferentiated trunk of biologi-
cal science that we confess no guilt of pre-
sumption in declaring boldly that whatever
difficulty may be in store for those who cast
in their lot with us, they need fear no dis-
illusionment or misgi\ang that their labour
has been wasted on a paltry quest.

In research, as in all business of explora-
tion, the stirring times come when a fi'esh
region is suddenly unlocked by the discovery
of a new key. Then conquest is easy and
there are prizes for all. We are happy in
that during our own time not a few such
territories have been revealed to the vision of
mankind. I do not dare to suggest that in
magnitude or splendour the field of Genetics
may be compared with that now being dis-
closed to the physicist or the astronomer;
for the glory of the celestial is one and the
glory of the terrestrial is another. But I will

1—2

THE METHODS AND

say that for once to the man of ordinary
power who cannot venture into those heights
beyond, Mendel's clue has shown the way into
a realm of nature which for surprising novelty
and adventure is hardly to be excelled.

i^ It is no hyperbolical figure that I use
when I speak of Mendelian discovery leading
us into a new world, the very existence of
which was unsuspected before. \

The road thither is simple and easy to
follow. We start from a common fact,
familiar to everyone, that all the ordinary
animals and plants began their individual
life by the union of two cells, the one male,
the other female. Those cells are known as
germ-cells or gametes, that is to say, " marry-
ing " cells.

Now obviously the diversity of form which
is characteristic of the animal and plant world
must be somehow represented in the gametes,
since it is they which bring into each organism

SCOPE OF GENETICS

all that it contains. I am aware that there is
interplay between the organism and the cir-
cumstances in which it grows up, and that
opportunity given may bring out a potenti-
ality which without that opportunity must
have lain dormant. But w hile noting paren-
thetically that this question of opportunity
has an importance, which some day it may be
convenient to estimate, the one certain fact is
that all the powers, physical and mental that
a living creature possesses were contributed
by one or by both of the two germ-cells which
united in fertilisation to give it existence.
The fact that tvjo cells are concerned in the
production of all the ordinary forms of life
was discovered a long while ago, and has
been part of the common stock of elementary
knowledge of all educated persons for about
half a century. The full consetpiences of this
double nature seem nevertheless to have
struck nobody before Mendel. Simple though

6 THE METHODS AND

the fact is, I have noticed that to many it is
difficult to assimilate as a working idea. _ We
are accustomed to think of a man, a butterfly,
or an apple tree as each one thing. In order
to understand the significance of Mendelism
we must get thoroughly familiar with the fact
that they are each two things, double through-
out every part of their composition. There
is perhaps no better exercise as a preparation
for genetic research than to examine the
people one meets in daily life and to try in a
rough way to analyse them into the two as-
semblages of characters which are united in
them. That we are assemblages or medleys
of our parental characteristics is obvious.
We all know that a man may have his father's
hair, his mother's colour, his father's voice,
his mother's insensibility to music, and so on,
but that is not enough.

Such an analysis is true, inasmuch
as the various characters are transmitted

SCOPE OF GENETICS

independently, but it misses the essential point.
For in each of these respects the individual is
double; and so to get a true picture of the
composition of the individual we have to think
how each of the two original gametes was pro-
vided in the matter of height, hair, colour,
mathematical ability, nail-shape, and the other
features that go to make the man we know.
The contribution of each gamete in each
respect has thus to be separately brought to
account. If we could make a list of all the
ingredients that go to form a man and could
set out how he is constituted in respect of
each of them, it Avould not suffice to give one
column of values for these ingredients, but
we must rule two columns, one for the ovum
and one for the spermatozoon, which united
in fertilisation to fonn that man, and in each
column we must represent how that gamete
was supplied in respect of each of the in-
gredients in our list. When the problem of

8 THE METHODS AND

heredity is thus represented we can hardly
avoid discovering, by mere inspection, one
of the chief conclusions to which genetic
research has led. For it is obvious that the
contributions of the male and female gametes
may in respect of any of the ingredients be
either the same, or different. In any case in
which the contribution made by the two cells
is the same, the resulting organism — in our
example the man — is, as we call it, pure-bred
for that ingredient, and in all respects in
which the contribution from the two sides
of the parentage is dissimilar the resulting
organism is cross-bred.

To give an intelligible account of the
next step in the analysis without having
recourse to precise and technical language
is not very easy.

We have got to the point of view from
which we see the individual made uj) of
a large number of distinct ingredients,

SCOPE OF GENETICS 9

contributed from two sources, and in respect of
any of them he may have received two similar
portions or two dissimilar portions. We shall
not go far wrong if we extend and elaborate
our illustration thus. Let us imagine the
contents of a gamete as a fluid made by
taking a drop from each of a definite number
of bottles in a chest, containing tinctm^es of
the several ingredients. There is one such
chest from which the male gamete is to be
made up, and a similar chest containing a
corresponding set of bottles out of which the
components of the female gamete are to be
taken. But in either chest one or more of
the bottles may be empty; then nothing
goes in to represent that ingredient from
that chest, and if corresponding bottles are
empty in both chests, then the individual
made on fertilisation by mixing the two
collections of drops together does not con-
tain the missing ingredient at all. It follows

^^

10 THE METHODS AND

therefore that an individual may thus be
"pure-bred," namely alike on both sides of
his composition as regards each ingredient
in one of two ways, either by having received
the ingredient from the male chest and from
the female, or in having received it from
neither. Conversely in respect of any in-
gredient he may be "cross-bred," receiving
the presence of it fi'om one gamete and the
absence of it from the other.

The second conception with which we
have now to become thoroughly familiar is
that of the individual as composed of what
we call presences and absences of all the
possible ingredients. It is the basis of all
progress in genetic analysis. Let me give
you two illvLstrations. A blue eye is due to
the absence of a factor which forms pigment
on the front of the iris. Two blue-eyed
parents therefore, as Hurst has proved, do
not have dark-eyed children. The dark eye

SCOPE OF GENETICS 11

is due to either a single or double dose of
the factor missing from the blue eye. So
dark-eyed persons may have families all dark-
eyed, or families composed of a mixture of
dark and light-eyed children in certain pro-
portions which on the average are definite.

Two plants of Oenothera which I exhibit
illustrate the same thing. One of them is
the ordinary Lmnarckiana. I bend its stem.
It will not break, or only breaks with diffi-
culty on account of the tough fibres it con-
tains. The stem of the other, one of de
Vries' famous mutations, snaps at once like
short pastry, because it does not contain the
factor for the formation of the fibres. Such
plants may be sister-plants produced by the
self-fertilisation of one parent, but they are
distinct in their composition and properties
— and this distinction turns on the presence
or absence of elements which are treated as
definite entities when the germ-cells are

12 THE METHODS AND

formed. When we speak of such qualities as
the formation of pigment in an eye, or the
development of fibres in a stem, as due to
transmitted elements or factors, you will per-
haps ask if we have formed any notion as to
the actual nature of those factors. For my
own part as regards that ulterior question I
confess to a disposition to hold my fancy on
a tight rein. It cannot be very long before
we shall knoiv what some of the factors are,
and we may leave guessing till then. Mean-
Avhile however there is no harm in admitting
that several of them behave much as if
they were ferments, and others as if they
constructed the substances on which the fer-
ments act. But we must not suppose for a
moment that it is the ferment, or the objective
substance, which is transmitted. The thing
transmitted can only be the power or faculty
to produce the ferment or the objective
substance.

SCOPE OF GENETICS 13

So far we have been considering the
synthesis of the individual from ingredients
brought into him by the two gametes. In
the next step of our consideration we reverse
the process, and examine how the ingredients
of which he was originally compounded are
distributed among the gametes that are
eventually budded off from him.

Take first the case of the components in
respect of which he is pure-bred. Expec-
tation would naturally suggest that all the
germ-cells formed from him would be alike
in respect of those ingredients, and obser-
vation shows, except in the rare cases of
originating variations, the causation of which
is still obscure, that this expectation is
correct.

Hitherto though without experimental
evidence no one could have been certain
that the facts were as I have described them,
yet there is nothing altogether contrary to

14 THE METHODS AND

common expectation. But when we proceed
to ask how the germ-cells will be constituted
in the case of an individual who is cross-bred
in some respect, containing that is to say, an
ingredient from the one side of his parentage
and not from the other, the answer is entirely
contrary to all the preconceptions which either
science or common sense had formed about
heredity. For we find definite experimental
proof in nearly all the cases which have been
examined, that the germ-cells formed by such
individuals do either contain or not contain a
representation of the ingredient, just as the
original gametes did or did not contain it.

[~If both parent-gametes brought a certain
quality in, then all the daughter gametes
have it ; if neither brought it in, then none
of the daughter gametes have it. If it came
in from one side and not from the other, then
on an average in half the resulting gametes
it will be present and from half it will be

SCOPE OF GENETICS 15

absent. This last phenomenon, which is
called segregation, constitutes the essence of
Mendel's discovery. \

So recurring to the simile of the man as
made by the mixing of tinctures, the process
of redistribution of his characters among the
germ-cells may be represented as a sorting
back of the tinctures again into a double row
of bottles, a pair corresponding to each in-
gredient ; and each of the germ-cells as then
made of a drop from one or other bottle
of each pair : and in our model we may repre-
sent the phenomenon of segregation in a
crude way by supposing that the bottles
having no tincture in them, instead of being
empty contained an inoperative fluid, say
water, with which the tincture would not mix.
When the new germ-cells are formed, the two
fluids instead of diluting each other simply
separate again. It is this fact which entitles
us to speak of the purity of germ-cells. They

16 THE METHODS AND

are pure in the possession of an ingredient,
or in not possessing it ; and the ingredients,
or factors, as we generally call them, are units
because they are so treated in the process of
formation of the new gametes and because
they come out of the process of segregation
in the same condition as they went in at
fertilisation.

As a consequence of these facts it follows
that however complex may be the origin of
two given parents the composition of the off-
spring they can produce is limited. There is
only a limited number of types to be made
by the possible recombinations of the parental
ingredients, and the relative numbers in which
each type will be represented are often pre-
dicable by very simple arithmetical rules.

For example, if neither parent possesses
a certain factor at all, then none of the off-
spring will have it. If either parent has two
doses of the factor then all the children will

SCOPE OF GENETICS 17

have it ; and if either parent has one dose of
the factor and the other has none, then on
an average half the family will have it, and
half be without it.

To know whether the parent possesses
the factor or not may be difficult for reasons
which will presently appear, but often it is
quite easy and can be told at once, for there
are many factors which cannot be present in
the individual without manifesting their pre-
sence. I may illustrate the descent of such
a factor by the case of a family possessing
a peculiar form of night-blindness. The
affected individuals marrying with those
unaffected have a mixture of affected
and unaffected children, but their unaffected
children not having the responsible ingredi-
ent cannot pass it on^

• ITie investigation of this remarkable family vins made
originally by Cunier. The facts have been reexamined and the
pedigiee niuch extended by Nettleship. The numerical results
are somewhat irregular, but it is especially interesting as being

B. 2

18 THE METHODS AND

In such an observation two things are
strikingly exemplified, (1) the fact of the
permanence of the unit, and (2) the fact that
a mixture of types in the family means that
one or other parent is cross-bred in some
respect, and is giving off gametes of more
than one type.

The problem of heredity is thus a problem
primarily analytical. We have to detect and
enumerate the factors out of which the bodies
of animals and plants are built up, and the
laws of their distribution among the germ-
cells. All the processes of which I have
spoken are accomplished by means of cell-
divisions, and in the one cell-union which
occurs in fertilisation. If we could watch

the largest pedigree of human disease or defect yet made. It
contains 2121 persons, extending over ten generations Of these
persons, 135 are known to have been night-blind. In no single
CJise was the peculiarity transmitted through an unaffected
member. It should be mentioned that for night-blindness such
a system of descent is peculiar. More usually it follows the
scheme described for coloin-blindness. It is not known wherein
the peculiarity of this family consists.

SCOPE OF GENETICS 19

the factors segregating- from each other in
cell-division, or even if by microscopic ex-
amination we could recognize this multitu-
dinous diversity of composition that must
certainly exist among the germ-cells of all
ordinary individuals, the work of genetics
would be much simpler than it is.

But so far no such direct method of
observation has been discovered. In default
we are obliged to examine the constitution
of the germ-cells by experimental breeding,
so contrived that each mating shall test the
composition of an individual in one or more
chosen respects, and, so to speak, sample its
germ -cells by counting the number of each
kind of offspring which it can produce. But
cumbersome as this method must necessarily
be, it enables us to put questions to Nature
which never have been put before. She, it
has been said, is an unwilling witness. Our
questions must be shaped in such a way that

2—2

20 THE METHODS AND

the only possible answer is a direct " Yes'' or
a direct "No." By putting such questions
we have received some astonishing answers
which go far below the surface. Amazing
though they be, they are nevertheless true ;
for though our witness may prevaricate, she
cannot lie. Piecing these answers together,
getting one hint from this experiment, and
another from that, we begin little by little to
reconstruct what is going on in that hidden
world of gametes. As we proceed, like our
brethren in other sciences, we sometimes re-
ceive answers which seem inconsistent or even
contradictoiy. But by degrees a sufficient
body of evidence can be attained to show
what is the rule and what the exception.
My purpose today must be to speak
rather of the regular than of the irregular.
One clear exception I may mention.
Castle finds that in a cross between the
long-eared lop-rabbit and a short-eared

SCOPE OF GENETICS 21

breed, eai*s of intermediate length are pro-
duced : and that these intermediates breed
approximately true.

Exceptions in general must be discussed
elsewhere. Nevertheless if I may throw out
a word of counsel to beginners, it is : Treasure
your exceptions! When there are none,
the work gets so dull that no one cares to
carry it further. Keep them always un-
covered and in sight. Exceptions are like
the rough brickwork of a growing building
which tells that there is more to come and
shows where the next construction is to be. _

You will readily understand that the
presentation here given of the phenomena
is only the barest possible outline. Some of
the details we may now fill in. For example,
I have spoken of the characters of the
organism, its colour, shape, and the like, as if
they were due each to one ingredient or factor.
Some of them are no doubt correctly so

22 THE METHODS AND

represented ; but already we know numerous
bodily features which need the concurrence
of several factors to produce them. Never-
theless though the character only appears
when all the complementary ingredients are
together present, each of these severally and
independently follows, as regards its trans-
mission, the simple rules I have described.
This complementary action may be illus-
trated by some curious results that Mr
Punnett and I have encountered when ex-
perimenting with the height of Sweet Peas.
There are two dwarf varieties, one the
prostrate "Cupid," the other the half-dwarf
or "Bush" Sweet Peas. Crossed together
they give a cross-bred of full height. There
is thus some element in the Cupid which
when it meets the complementaiy element
from the Bush, produces the characteristic
length of the ordinary Sweet Pea. We may
note in passing that such a fact demonstrates

SCOPE OF GENETICS 23

at once the nature of Variation and Rever-
sion. The Reversion occm*s because the two
factors that made the height of the old Sweet
Pea again come together after being parted :
and the Variations by which each of the
dwarfs came into existence must have taken
place by the dropping out of one of these
elements or of the other.

Conversely there are factors which by
their presence can prevent or inhibit the
development and appearance of others pre-
sent and unperceived.

For example, all the factors for pigmen-
tation may be present in a plant or an
animal; but in addition there may be
another factor present which keeps the
individual white, or nearly so.

There are cases in which the action of
the factors is superposed one on top of the
other, and not until each factor is removed
in turn can the effects of the underlying

^mm

24 THE METHODS AND

factors be perceived. So in the mouse if
no other colour-factor is present, the fur is
chocolate. If the next factor in the series be
there, it is black. If still another factor be
added, it has the brownish grey of the common
wild mouse. Conversely, by the variation
which dropped out the top factor, a black
mouse came into existence. By the loss of
the black factor, the chocolate mouse was
created, and for aught we can tell there may
be still more possibilities hidden beneath.

In the disentanglement of the properties
and interactions of these elementaiy factors,
the science we must call to our aid is
Physiological Chemistry. The relations of
Genetics with the other branches of biology
are close. 8uch work can only be conducted
by those who have the good fortune to be able
to count upon continual help and advice from
specialists in the various branches of Zoo-
logy, Physiology, and Botany. Often we have

SCOPE OF GENETICS 25

questions with which only a cytologist can
deal, and often it is the experience of a
systematist we must invoke. The school of
Genetics in Cambridge starts under happy
auspices in that we are surrounded by col-
leagues qualified, and as we have often found,
willing to give us such aid unstinted. But
with chemical physiology, we stand in an
even closer relation; and fi'om the little I
have dared to say respecting the action and
interaction of factors, it is evident that for
their disentanglement there must one day
be an intimate and enduring partnership
arranged with the physiological chemists.

Now, as the whole of the elaborate process
by which the various elements are appor-
tioned among the gametes must be got
through in a few cell-divisions at most, and
perhaps in one division only, it is not sur-
prising that there is sometimes an interaction
between factors that have quite distinct roles

26 THE METHODS AND

to perform. These interactions are probably
of several kinds. One, which I shall illus-
trate presently, is probably to be represented
as a repulsion between two factors. As a
consequence of its operations when the
various factors are sorted out into the gametes,
if the individual be cross-bred in respect of
the two repelling factors, having received so
to speak only a single dose of each, then the
gametes are made up in such a way that each
takes one or other of the two repelling factors,
not both.

Mutual repulsions of this kind probably
play a significant part in the phenomena of
heredity. A single concrete case which Mr
Punnett and I have been investigating for
some years will illustrate several of these
principles. We crossed together a pure
white Sweet Pea having an erect standard,
with another pure white Sweet Pea having a
hooded standard. The result is, as you see,

SCOPE OF GENETICS 27

a purple flower with an erect standard. The
colour comes from the concurrence of com-
plementary elements. A dose of a certain
ingredient from one parent meets a dose of
another ingredient from the other parent
and the two make pigment in the flower.
From other experiments we know that the
purple colour of the pigment is due to a
dose of a third ingredient brought in from
the hooded parent ; and that in the absence
of that blue factor, as we may call it, the
flower would be red. The standard is erect
because it contains a dose of the erectness-
factor from the erect parent, and the hooded
parent can readily be proved to owe its
peculiar shape to the absence of that
element.

Our purple plant is thus cross-bred for
four factors, containing only one dose of

each.

We let it fertilise itself, and its oflspring

28 THE METHODS AND

show all the possible combinations of the
four different factors and their absences
which the genetic constitution of the plant
can make.

Note that one of the combinations we
expect to find is missing. There are white
erect and white hooded — white because they
are lacking one or other of the comple-
mentary ingredients necessary to the pro-
duction of pigment. There are purple erect
and purple hooded, of which the purple erect
must perforce contain all the four factors,
and the puq^le hooded must similarly con-
tain all of them except that for erectness.
But when we turn to the red class we are
surprised to find that they are all erect, none
hooded. One of the possible combinations
is missing. If you examine this series of
facts you will find there is only one possible
interpretation : namely that the ingredient
which turns the flower purple — alkalinity.

SCOPE OF GENETICS 29

perhaps Ave may call it — never goes into the
same germ-cell as the ingredient which makes
the standard erect. There are plenty of ways
of testing the truth of this interpretation.
For example, it follows that the purple
erects from such a family >vill in perpetuity
have offspring 1 purple hooded: 2 purple
erect : 1 red erect; also that all the white
hooded crossed with pure reds will give
purples, and so on. These experiments have
been made and the result has in each case
been conformable to expectation.

Between these two factors, the purpleness
and the erectness of standard, some antago-
nism or repulsion must exist. In some way
therefore the chemical and the geometrical
phenomena of heredity must be inter-related.

Some one will say perhaps this is all very
well as a scientific curiosity, but it has nothing
to do with real life. The right answer to such
criticism is of course the lofty one that science

30 THE METHODS AND

and its applications are distinct: that the
investigator fixes his gaze solely on the search
for truth and that his attention must not be
distracted by trivialities of application. But
while we make this answer and at least try to
work in the spirit it proclaims, we know in
our hearts that it is a counsel of perfection. I
suspect that even the astronomer who at his
spectroscope is analysing the composition of
Vega or Capella has still an eye sometimes free
for the affairs of this planet, and at least the
fact that his discoveries may throw light on
our destinies does not diminish his zeal in their
pursuit. And surely to the study of Heredity,
preeminently among all the sciences, we are
looking for light on human destiny. To
pretend otherwise would be mere hypocrisy.
So while reserving the higher line of defence
I will reply that again and again in our
experimental work we come very near indeed
to human affairs. Sometimes this is obvious

SCOPE OF GENETICS 31

enough. No practical dog-breeder or seeds-
man can see the results of Mendelian recom-
bination without perceiving that here is a bit
of knowledge he can immediately apply. No
sociologist can examine the pedigrees illus-
trating the simple descent of a deformity or
a congenital disease, and not see that the
new knowledge gives a solid basis for prac-
tical action by which the composition of a
race could be modified if society so chose.
More than this : we know for certain in one
case, from the work of Professor BifFen, that
the power to resist a disease caused by the
invasion of a pathogenic organism, wheat-
rust, is due to the absence of one of the
simple factors or ingredients of which I have
spoken, and what we know to be true in that
one case we are beginning to suspect to be
true of resistance to certain other diseases.
No pathologist can see such an experiment
as this of Professor Biffen's without realizing

32 THE METHODS AND

that here is a contribution of the first im-
portance to the physiology of disease.

There is no lack of utility and direct
application in the study of Genetics. I have
alluded to some strictly practical results. If
we want to raise mangels that will not run to
seed, or to breed a cow that will give more
milk in less time, or milk with more butter
and less water, we can turn to Genetics with
every hope that something can be done in
these laudable directions. But here I would
plead what I cannot but regard as a higher
usefulness in our work. Genetic inquiry aims
at providing knowledge that may bring, and
I think will bring, certainty into a region
of human affairs and concepts which might
have been supposed reserved for ages to be
the domain of the visionary. We have long
known that it was believed by some that our
powers and conduct were dependent on our
physical composition, and that other schools

SCOPE OF GENETICS 33

have maintained that nurture not nature, to
use Galton's antithesis, has a preponderating
influence on our careers; but so soon as it
becomes common knowledge — not a philo-
sophical speculation, but a certainty — that
liability to a disease, or the power of resisting
its attack, addiction to a particular vice, or to
superstition, is due to the presence or absence
of a specific ingredient ; and finally that these
characteristics are transmitted to the off-
spring according to definite, predicable rules,
then man's views of his own nature, his con-
ceptions of justice, in short his whole outlook
on the world, must be profoundly changed.
Yet as regards the more tangible of these
physical and mental characteristics there can
be little doubt that before many years have
passed the laws of their transmission will be
expressible in simple formulae.

The blundering cruelty we call criminal
Justice will stand forth divested of natural

B- 3

34 THE METHODS AND

sanction, a relic of the ferocious inventions of
the savage. Well may such justice be por-
trayed as blind. Who shall say whether it is
crime or punishment which has wrought the
greater suffering in the world ? We may live
to know that to the keen satirical vision of Sam
Butler on the pleasant mountains of Erewhon
there was revealed a dispensation, not kinder
only, but wiser than the temfic code which
Moses delivered from the flames of Sinai.

If there are societies which refuse to apply
the new knowledge, the fault will not lie with
Genetics. I think it needs but little observa-
tion of the newer civilisations to foresee that
they will apply every scrap of scientific know-
ledge which can help them, or seems to
help them in the struggle, and I am good
enough Selectionist to know that in that day
the fate of the recalcitrant communities is
sealed.

The thrill of discovery is not dulled

^H«^

SCOPE OF GENETICS 35

by a suspicion that the discovery can be
applied. No harm is done to the investigator
if he can resist the temptation to deviate
fiom his aim. With rarest exceptions the
discoveries which have formed the basis
of physical progress have been made without
any thought but for the gratification of
curiosity. Of this there can be few examples
more conspicuous than that which Mendel's
work presents. Untroubled by any itch to
make potatoes larger or bread cheaper, he set
himself in the quiet of a cloister garden to find
out the laws of hybridity, and so struck a mine
of truth, inexhaustible in brilliancy and profit.
I will now suggest to you that it is by no
means unlikely that even in an inquiry so
remote as that which I just described in the
case of the Sweet Pea, we may have the clue
to a mystery which concerns us all in the
closest possible way. I mean the problem of
the physiological nature of Sex. In speaking

3—2

36 THE METHODS AND

of the interpretation of sexual difference sug-
gested by our experimental work as of some
practical moment, I do not imply that as in
the other instances I have given, the know-
ledge is likely to be of immediate use to our
species ; but only that if true it makes a con-
tribution to the stock of human ideas which
no one can regard as insignificant.

In the light of Mendelian knowledge, when
a family consists of more than one type the
fact means that the germ-cells of one or other
parent must certainly be of more than one
kind. In the case of sex the members of the
family are thus of two kinds, and the pre-
sumption is overwhelming that this distinction
is due to a difference among the germ-cells.
Next, since for all practical purposes the
numbers of the two sexes produced are
approximately equal, sex exhibits the special
case in which a family consists of two types
represented in equal numbers, half being

SCOPE OF GENETICS 37

male, half female. But I called your attention
to the fact that equality of types results when
one parent was cross-bred in the character
concerned, having received one dose only of
the factor on which it depends. So we may
feel fairly sure that the distinction between
the sexes depends on the presence in one
or other of them of an unpaired factor.
This conclusion appears to me to follow
so immediately on all that we have learnt of
genetic physiology that w ith every confidence
we may accept it as representing the actual
fact.

The (question which of the two sexes
contains the unpaired factor is less easy to
answer, but there are several converging lines
of evidence which point to the deduction that
in Vertebrates at least, and in some other
types, it is the female, and I feel little doubt
that we shall succeed in proving that in them
femaleness is a definite Mendelian factor

38 THE METHODS AND

absent from the male and following the
ordinary Mendelian rules.

Before showing you how the Sweet Pea
phenomenon aids in this inquiry I must tell
you of some other experimental results. The
fii'st concerns the common currant moth,
Abraxas grossulariaia. It has a definite
pale variety called lacficolor. With these
two forms Doncaster has made a remarkable
series of experiments. When he began, lacti-
eolor was only known as a female form. This
was crossed with the grossulariata male and
gave grossulariata only, showing that the
male was pure to type. The hybrids bred
together gave grossulariata males and females
and lacticolor females only. But the hybrid
males bred to lacticolor females produced
all four combinations, grossulariata males
and females, and lacticolor males and females.
When the la^^ticolor males were bred to gros-
sulariata females, whether hybrid, or wild

SCOPE OF GENETICS 39

from a district where lacticolor does not
exist, the result was that all the males were
gi'ossidariata and all the females lacticolor \
It is difficult to follow the course of such an
experiment on once hearing and all I ask
you to remember is first that there is a series
of matings giving very curious distributions
of the characters of type and variety among
the two sexes. And then, what is perhaps
the most singular fact of all, that the wild
typical grossidarlata female can when crossed
with the lacticolor male produce all females
lacticolor. This last fact can, we know, mean
only one thing, namely that these wild females
are in reality hybrids of lacticolor \ though
since the males are pure grossulariata, that
fact would in the natural course of things
never be revealed.

When we encounter such a series of
phenomena as this, our business is to find
a means of symbolical expression which will

r-^-

40 THE METHODS AND

represent all the factors involved, and show
how each behaves in descent. Such a system
or scheme we have at length discovered, and
I incline to think that it must be the true
one. If you study this case you will find that
there are nine distinct kinds of matings that
can be made between the variety, the type
and the hybrid, and the scheme fits the whole
group of results. It is based on two suppo-
sitions :

1. That the female is cross-bred, or as
we call it heterozygous for femaleness-factor,
the male being without that factor. The eggs
are thus each destined fi'om the first to be-
come either males or females, but as regards
sex the spermatozoa are alike in being non-
female.

2. That there is a repulsion between the
femaleness-factor and the grossnlariata factor.

Such a repulsion between two factors we
are Justified in regarding as possible because

-^mm^mmmmm

SCOPE OF GENETICS 41

we have had proof of the occurrence of a
similar repulsion in the case of the two
factors in the Sweet Pea.

If the case of this moth stood alone it
would be interesting", but its importance is
greatly increased by the fact that we know-
two cases in birds which are closely compar-
able. The simpler case to w hich alone I shall
refer has been observed in the Canary. Like
the Currant moth it has a kind of albino,
called Cinnamon, and males of this variety
when mated with ordinary dark green hen
canaries produce dark males and Cinnamons
which are always hens ; while the green male
and the Cinnamon hen produce nothing but
greens of both sexes. This case, which has
been experimentally studied by Miss Durham,
offers a certain complication, but in its main
outlines it is exactly like that of the moth,
and the same interpretation is applicable to
both.

42 THE METHODS AND

The particular interpretation may be im-
perfect and even partially wrong ; but that we
are at last able to form a working idea of the
course of such phenomena at all is a most
encouraging fact. If we are right, as I am
strongly inclined to believe, we get a glimpse
of the significance of the popular idea that in
certain respects daughters are apt to resemble
their fathers and sons their mothers ; a phe-
nomenon which is certainly sometimes to be
observed.

There are several collateral indications
that we are on the right track in our theory
of the nature of sex. One of these, derived
from the peculiar inheritance of colour-
blindness, is especially interesting. That
affection is common in men, rare in women.
Men who are colour-blind can transmit the
affection but men who have normal vision
cannot. Women however who are ostensibly
normal may have colour-blind sons; and

SCOPE OF GENETICS 43

women who are colour-blind have, so far as
we know, no sons who are not colour-blind ^

Mendelian analysis of these facts shows
that colour-blindness is due, not, as might
have been supposed, to the absence of some-
thing from the composition of the body, but
to the presence of something which affects
the sight. Just as nicotine-poisoning can
paralyse the colour sense, so may we conceive
the development of a secretion in the body
which has a similar action. The comparative
exemption of the woman must therefore mean
that there is in her a positive factor which
counteracts the colour-blindness factor, and
it is not improbable that the counteracting
element is no other than the femaleness-
factor itself 2.

' We have knowledge now of seven colour-blind women,
having, in all, 17 sons who are all colour-blind. Most of these
cases have been collected by Mr Xettleship.

* An alternative and perhaps more satisfactory interpretation
of the ssime facts h:is been proposed by Doncaster {Jour. Genetics i,
Pt 4, p. 377). Until more progress has been made with the

44 THE METHODS AND

I think I have said enough to prove that
after all, those curiosities collected from ob-
servation of Sweet Peas and Canaries have
no remote bearing on some very fascinating
problems of human life.

Lastly I suppose it is self-evident that
they have a bearing on the problem of Evo-
lution. The facts of heredity and variation
are the materials out of which all theories of
Evolution are constructed. At last by genetic
methods we are beginning to obtain such
facts of unimpeachable quality, and free
from the flaws that were inevitable in older
collections. From a survey of these materials
we see something of the changes which will
have to be made in the orthodox edifice to

analysis of sexual differentiation it is not possible to decide which
of the two interpretations is correct. The uumencal results
predicted on l)oth systems are the same ; but by introducing a
more complicated though quite reasonable formula for the
representation of the sex-ditferences Doncaster's method shows
that colour-blindness may be a recessive due to the absence of a
factor which produces normal colour-vision.

fiai

SCOPE OF GENETICS 45

admit of their incorporation, but he must be
rash indeed who would now attempt a com-
prehensive reconstruction. The results of
genetic research are so bewilderingly novel
that we need time and an exhaustive study
of their inter-relations before we can hope
to see them in proper value and perspective.
In all the discussions of the stability and
fitness of species who ever contemplated
the possibility of a wild species having one
of its sexes permanently hybrid? When I
spoke of adventures to be encountered in
genetic research I was thinking of such
astonishing discoveries as that.

There are others no less disconcerting.
Who would have supposed it possible that
the pollen-cells of a plant could be all of one
type, and its egg-cells of two types? Yet
Miss Saunders' experiments have provided
definite proof that this is the condition
of certain Stocks, of which the pollen grains

46 THE METHODS AND

all bear doubleness, while the egg-cells are
some singles and some doubles. We can-
not think yet of interpreting these complex
phenomena in terms of a common plan.
All that we know is that there is now open
for our scrutiny a world of varied, orderly
and specific physiological wonders into which
we have as yet only peeped. To lay down
positive propositions as to the origin and
inter-relation of species in general, now, would
be a task as fruitless as that of a chemist
must have been who had tried to state the
relationship of the elements before their
properties had been investigated.

For the first time Variation and Reversion
have a concrete, palpable meaning. Hitherto
they have stood by in all evolutionary debates,
convenient genii, ready to perform as little or
as much as might be desired by the conjuror.
That vaporous stage of their existence is
over; and we see Variation shaping itself as

BHI

SCOPE OF GENETICS 47

a definite, physiological event, the addition or
omission of one or more definite elements;
and Reversion as that particular addition or
subtraction which brings the total of the
elements back to something it had been
before in the history of the race.

The time for discussion of Evolution as
a problem at large is closed. We face that
problem now as one soluble by minute, critical
analysis. Lord Acton in his inaugural lecture
said that in the study of history we are at the
beginning of the documentary age. No one
will charge me with disrespect to the great
name we commemorate this year, if I apply
those words to the history of Evolution:
Darwin, it was, who first showed us that the
species have a history that can be read at all.
If in the new reading of that history, there
be found departures from the text laid down
in his first recension, it is not to his fearless
spirit that they will bring dismay.

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■JnaAiiM m 1

BioMed

Bateson, William

The methods and scope of
genetics

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