w_ru t)- w ::: =::=: ::r 0 _ u ::r (1) - - M ..D ..D U ==== M ru "": _ 0 (1) ===== U. :::;;::::;;;:;; o = - ...D (ñ= ("'- ffi - M ? - fT1 . ..... ". . , .1 L. ST LINK au. PRESENT NOWLEDGE OF THE DESCENl: OF MAN , .' I I ErE EXLIBRIS BERTRAN\.C.A WINDLE D.Se. M.D d .-. '[ I-I f LA'\S'1' L IN I{ THE LAST LINK OUR PRESENT KNOWLEDGE OF THE DESCENT OF l\tfAN BY ERNST HAECKEL (JEXA) WITH NOTES .\.ND BIO( R.\PHIc.\L Sh..ETCHES BV HANS GAD OW, F.R.S. (CA1\IBRIUGE) LONDON ADAM AND CHARLES BLACK 18 9 8 JUN g 1958 CONTENTS rA(j THE LAST LINK. INTRODUCTORY COl\IP.\RATIVE ANATOl\IY PALÆONTOLOGY OTHER EVIDENCE STAGES RECAPITUL.\TED BIOGRAPHICAL SIZETCHES:. 1 8 20 4 2 47 LAMARCK, SAINT - HILAIRE, CUVIER, BAER, MUELLER, VIRCHOW, COPE, KOELLIKER, GEGEN- BAUR, HAECKEL THEORY OF CELLS F.-\CTORS OF EVOLUTION GEOLOGICAL TI\IE AND EVOI UTIOX 80 115 117 135 NO'T'E THE address I delivered on August 26 at the Fourth I nternational Congress of Zc\ology at Carnbridge, 'On our Present Know'ledge of the Descent of Man,' has, I find, fruin the high significance of the theme and the general in1portance of the questions con- nected with it, excited much interest, and has led to requests for its publication. Hence this volun1e, edited by my friend Dr. H. Gadow, my pupil in earlier days, w'ho has not only revised the text, but has also enriched it by many valuable additions and notes. ERNST HAECKEL. /Clla, December, 1898. THE LAST LINK A T the end of the nineteenth century, the age of 'natural science,' the department of know'ledge that has made most progress is zoology. From zoology has arisen the study of transformisn1, which now dominates the whole of biology. Lamarck* laid its founda- tion in 1809, and forty years ago Charles Darwin obtained for it a recognition which is now universa1. I t is not my task to repeat the well-known principles of Darwinism. I am not concerned to explain the scientific value of the whole theory of descent. The whole of our biological study is pervaded by it. No general problem in zoology and * See note, p. 80. I 2 THE LAST LINK botany, In anatomy and physiology, can be discussed without the question arising, How has this problem originated? What are the real causes of its development? This question \vas almost unknown seventy years ago, when Charles Darwin, the great reformer of biology, began his academical career at Cambridge as a student of theology. In the same year, 1828, Carl Ernst von l aer* published in Germany his classical work on the embryology of animals, the first successful attempt to elucidate by 'obser- vation and reflection' the mysterious origin of the anin1al body fron1 the egg, and to explain in every respect the 'history of the growing individuality.' Darwin at that time had no knowledge of this great advance, and he could not divine that forty years later embryology w'ould be one of the strongest supports of his own life's work-of that very theory of transformism which, founded by Lamarck in the year of Darwin's birth, * See note, p. 89. HISTORY OF TRAiVSFORMISl'rI 3 was accepted with enthusiasm by Charles's grandfather Erasmus. There is no doubt that of all the celebrated naturalists of the nineteenth century Darwin achieved the greatest success, and we should be justified in designating the last forty years as the Age of Darwin. I n searching for the causes of this un- exampled success, we must clearly separate three sets of considerations: first, the compre- hensive reforlTI of Lamarck's transforn1ism, and its firm establishment by the many arguments drawn from modern biology; secondly, the construction of the new theory of selection, as established by Darwin, and independentlý by Alfred V\T all ace (a theory called Darwinism in the proper sense); thirdly, the deduction of anthropogeny, that most important conclusion of the theory of descent, the value of which far surpasses all the other truths in evolution. I t is the third point of Darwin's theory that I shall discuss here; and I shall discuss 1-2 4 THE LAST LINK it chiefly with the intention of exam1l11ng critically the evidence and the different conclusions which at present represent our scientific knowledge of the descent of n1an and of the different stages of his animal pedigree. I t is now generally admitted that this problem is the most important of all bio- logical questions. Huxley was right when in 1863 he called it the question of questions for mankind. The problem which underlies all others, and is more deeply interesting than any other, is as to the place which man occupies in nature and his relations to the universe of things. '\Vhence our race has come; what are the lin1its of onr power over nature, and of nature's power over us; to what goal are we tending-these are the problems which present thenlselves ane\v and with undiminished interest to every Inan born into the world.' 1"'his impressive view was eXplained by Huxley thirty-five years ago in his three celebrated essays on ' Evidence HISTORY OF TRANSFOR1JIIS11I 5 as to 1Ylan's Place in Nature.' The first IS entitled' On the Natural History of the Man- like Apes'; the second, 'On the Relations of l\lan to the Lower Animals'; the third, 'On some Fossil Remains of Man.' Darwin him- self felt the burden of these problems as much as Huxley; but in his chief work, 'On the Origin of Species,' in 1859, he had purposely only just touched them, suggesting that the theory of descent would shed light upon the origin of man and his history. Twelve years later, in his celebrated work on ' The Descent of Man, and Selection in Relation to Sex,' Darw'in discussed fully and ingeniously all the different sides of this 'question of questions' from the n10rphological, historical, physiological, and psychological points of View. As early as 1866 I myself had applied in the GeJlerllle l1forþhologie tier 0 rg-allislIlell the theory of transformism to anthropology, and had shown that the fundamental law' of biogeny claims the san1e value for lnan as for all the other animals. The intin1ate causal 6 THE LAST LINK connection between ontogeny and phylogeny, between the development of the individual and the history of its ancestors: enables us to gain a safe and certain kno\vledge of our ancestral series. I had at that tin1e distinguished in this series ten chief degrees of vertebrate organization. I attributed the highest im- portance to the logical connection of anthro- pogeny with transformism. If the latter be true, the truth of the fonl1er is absolute. 'Our theory that n1an is descended fron1 lower vertebrates, and imn1ediate]y fron1 apes or primates, is a case of special deductioll which follows w'ith absolute certainty fron1 the general -induction of the theory of descent.' The full proof and detailed ex planation of this view was afterwards given In Iny , History of Natural Creation,' and especially in my 'Anthropogeny.'* Lastly, it has received an alnple scientific and critical foundation in the third part of my 'Syste- matic Phylogeny.'* * See notes, pp. 102, 106. HISTORY OF TR.ANSFORiJIISJlI 7 During the forty years which have elapsed since Darwin's first pu blication of his theories an enormous literature, discussing the general þrobleJJts of transformism as well as its special application to man, has been published. In spite of the wide divergence of the different views, all agree in one main point: the natural developn1en t of man cannot be separ- ated from general transforn1isn1. There are only two possibilities. Either all the various species of anin1als and plants have been created independently by supernatural forces (and in this case the creation of n1an also is a n1iracle); or the species have been produced in a natural way by transmutation, by adapta- tion and progressive heredity (and in this case man also is descended from other verte- brates, and immediately from a series of primates). We are absolutely convinced that only the latter theory is fully scientific. '1'0 prove its truth, we have to examine critically the strength of the different arguments claimed for it. I. FIRST, we have to consider the relative place which comparative anatomy concedes to man in the 'natural systen1 ' of animals, for the true value of our 'natural classifica- tion' is based upon its meaning as a pedigree. All the minor and major groups of the system -the classes, legions, orders, îamilies, genera, and species-are only different branches of the same pedigree. F or man himself, his place in the pedigree has been fixed since Lan1arck, * in 180 I, defined the group of vertebrates. The most perfectt of these are * See note, p. 80. 'r Perfect, in the sense of highest stage of evolution, may seem a þetitio þrÙzciþii. Leaving aside the consideration that no living creature is absolutely perfect, in the sense that its organization cannot becOllle more efficient or proficient, we have here to deal with relative perfection of the whole 8 JL.1N .L1 PRL.1IATE 9 the l\lalnmalia; and at the head of this class stands the order of Primates, in which Lin- næus, in 1735. united four' genera '-Homo, Simia, Lemur, and Vespertilio. If we exclude the last-named, the Chiroptera of modern zoology, there remain three natural groups of Primates -the Lemures, the Silniæ, and the Anthropi or H ominidæ. This is the classifica- organization. A fish or a snake is in its way more specialized than a mammal; but specialization does not necessarily mean height of developn1ent : it generally means life in a comparatively narrow groove. The acts of giving birth and nourishing the young with the n10ther's milk is a much higher stage than the act of laying eggs and letting them run their chance. The developn1ent of a hairy coat goes along with heightened temperature of the blood, subsequent greater independence of the surrounding temperature, and increased steady activity of the brain and other nerve- centres. The brain of the l\lammalia, in its minute structure, is much more complex. This rule applies to son1e of the principal sense organs, chiefly the nose and the ear. The skeleton, not so much as a whole as in the various bones and joints, is more neatly finished, and built up n10re in conformity with' scientific principles,' than is the case even with birds, in spite of their marvellous specialization. The same is the case with the vascular system, notably the heart and the veins, and with the excretory organs. In all of these many imperfections, still to be found in the other classes, have been corrected in l\lammalia. The Primates take an easy first by their hands, and among them the apes and man himself by their brains. 10 THE LAST LI1\lK tion of the majority of zoologists; but if we con1pare n1an with the two chief groups of 1110nkeys-the Eastern monkeys (or Catar- rhinæ) and the \\T estern or American monkeys (Platyrrhinæ)-there can be no doubt that the fonner group is n1uch n10re closely related to man than is the latter. I n the natural order of the Catarrhinæ we find united a long series of lower and higher forms. The lowest, the Cynopitheci, appear still closely related to the Platyrrhinæ and to the Lemures; while, on the other hand, the tailless apes (Anthro- _ pomorphæ) approach man through their higher organization. Hence one of our best authorities on the Primates, Robert Hart- n1ann,* proposed to subdivide the whole order of the Simiæ into three groups: (I) Primarii, n1an together with the other Anthropornorphæ, or tailless apes; (2) Simiæ, all the other monkeys; (3) Prosimiæ, or Lemurs. This arrangement has received * 'Die menschenähnlichen Affen und ihre Organisation im VergIeich zur menschlichen.' 1883. JIA.l\T A PRill/ATE I I strong support from the interesting discovery by Selenka that the peculiar placentation of the human embryo is the saIne as in the great apes, and different froln that of all the other monkeys. Our choice between these different classifications of Primdtes is best àetermined by the important thesis of Huxley, in which, in 1863, he carried out a most careful and critical comparison of all the anatomical gradations within this order. I n my opinion, this ingenious thesis-which I have called tÌ1e H uxleyan Law, or the 'Pithecon1etra-thesis of Huxley '-is of the utn10st value. I t runs as follows: "rhus, whatever systen1 of organs be studied, the con1parison of their n1odifications in the ape- series leads to one and the same result - that the structural differences which separate Inan fron1 the gorilla a d the chimpanzee are not so great as those which separate the gorilla frotn the 10\\Ter apes.' If we accept the H uxleyan la\v without prejudice, and apply it to the natural classification of the Prilnates, we 12 THE LAST LINK must concede that man's place is within the order of the Simiæ. On examining this relation with care, and judging with logical persistence, we may even go a step further. I nstead of the wider conception of ' Simiæ,' we must use the restricted term of Catar- rhinæ, and our Pithecometra-thesis has then to be forn1ulated as follows: The cOJJzþarative anatoulY 0/ all organs of the grouþ of Catar- rhine SÙniæ leads to the result that the lIlorþhological differcnces between 1Jzan and the great aþes are ?lot so great as are those betweelt the Juan-like aþes and the lowest Catarrhi1læ. I n fact, it is very difficult to show why man should not be classed with the large apes in the san1e zoological fan1ily. \Ve all know a man from an ape; but it is quite another thing to find differences which are absolute and not of degree only. Speak- ing generally, we may say that nlan alone conlbines the four following features: (I) Erect walk; (2) extremities differentiated accordingly; (3) articulate speech; (4) higher lIfAN A PRIfrfA TE I'" .) reasoning power. Speech and reason are obviously relative distinctions only-the direct result of more brains and more brain-power, the so-called ll1en tal faculties. The erect walk is not an absolutely distinguishing character- istic: the large apes likewise walk on their feet only, supporting their bodies by touching the ground with the backs of their hands-in fact, with their knuckles-and this is a n10de of progression very different from that of the tailed 111onkeys, which walk upon the paltns of their hands. There are, however, two obvious differences in the developn1ent of the tnuscles. I n man alone the gastro- cnen1ius and the soleus muscle are thick enough to form the calf of the leg, and the glutæus maximus is enlarged into the buttocks. A fourth glutæal muscle occurs occasion2.lly in man, while it is constantly present in apes as the so-called musculus scansorlUS. Concerning the muscles of the whole body, we cannot do better than quote Testut's summary: 'The n1ass of recorded 14 THE LAST LINl{ observations upon the muscular anomalies in man is so great, and the agreement of many of these with the condition normal in apes is so marked, that the gap which usually separates the muscular systetn of man fronl that of the apes appears to be completely bridged over.' There are, for example, the muscles of the ear. In most people the majority, or even all of them, are no longer movable at will, while in the apes they are still in use. The itnportant point, however, is that these muscles are still present in tnan, although often in a reduced condition. They are the following: ( I) M Llscullls auricularis anterior or attrahens auris, which is frequently much reduced and no longer reaches the ear at all, being then absolutely useless; (2) IVI usculus auricularis superior or attollens auris, more constant than the former; (3) 1\1 usculus auricularis posterior or retrahens auris, like- wise often functional. Occasionally smaller slips differentiated from these three muscles are present, and as so-called intrinsic muscles f) X 4 -----... --- . I , , , , , , I . , x 6. OUTLINES OF THE LEFT EAR OF - I. Lemu.r lllacaCO; 2. .fi/Jacac1ts rhesus, the Rhesus monkey; 3. Cercopithecus, a macaque; 4. human embryo of six months; 5. man, with Darwin's point well retained: the doUeò outline is that of the ear of a baboon; 6. orang-utan (after G. Schwalbe):1 x the original tip of the ear; 7. human ear with the principal muscles. 1 G. Schwalbe, 'In wiefern ist die menschliche Ohrmuschel ein rudimentäres Organ ?'-In what Respects is the Human Outer Ear a Rudimentary Organ? (A rchlv f. A1zatomz"e u1zd Thysiologie, 1889). 16 THE LAST LINK are restricted to the ear itself; their function is, or was, that of curling up or opening the external ear. In connection with the ear, I may touch upon another interesting and rnost sugges. tive little feature which is present in many individuals-namely, 'Darwin's point.' This is the last retnnant of the original tip of the ear, before the outer, upper, and hinder rim becalne doubled up or folded in. I t is a feature quite useless, and absolutely impossible of interpretation, excepting as the vestige of such previous ancestral conditions as are nornlal in the monkeys. I n some cases the reduction of 111uscles has proceeded further in apes than in man-- for example, the muscles of the little toe. Another instance is afforded by the coccyx or vestige of the tail; this is still furnished with l11uscles which are now in ll1an, as well as in the apes, quite useless, and vary considerably with every sign of degeneration, most so in the orang-utan. JI.LV A fJRLJLITE 17 J!arwin has mentioned the frefJuent action of the' snarling muscle,' by which, in sneering, our upper canine teeth are exposed, like those of a dog prepared to fight. 1\lonkeys and apes possess vocal sacs, especially large in the orang-utan ; survivals of thetTI, although no longer used, persist in man in the shape of a pair of small di ver- ticula, the pouches of 1\lorgagni. between the true and the false vocal cords. , I n the native Australians, the dental for- Jnula appears least retnoved frOln the hypo- thetical original type, for in it are still found con1plete rows of splendid teeth, \\rith power- fully-developed canines and Inolars, the latter being either unifornl, or even increasing in size, as we proceed backwards, in such a way that the wisdoln tooth is the largest of the series. This is decidedly a pithecoid characteristic which is always found in apes. The upper incisors of the 1\Ialay, apart fron1 their prognatholls disposition, have occasion- ally a distinctly pithecoid fonn, their anterior 2 18 THE LAST L11'lK surface being convex, and their lingual sur- face slightly concave. The ancestors of Europeans seem to have had the same form of teeth, for the oldest existing fragments of skulls from the Mammoth age (e.g., the jaws from La N aulette, in Belgiun1) reveal tooth- forms which must be classed with those of the lowest races of to-day.' f.' N ow we are able to apply this fundamental Pithecometra-th sis directly to the classifica- tion of the Primates and to the phylogeny of man, which is intimately connected with it, because in this order, as in all the other groups of animals, the natural system is the clear expression of true phylogenetic affinity. Four results follow from our thesis: (I) The Prin1ates, as the highest legion or order of mammals, form one natural, monophyletic group. All the Lemures, Simiæ, and Homines descend from one common ances- * \Viedersheim, 'Der Bau des l'vlenschen als Zeugniss fÜr seine Vergangenheit.' Freiburg, 1888. Translated:' The Structure of 1\1 an an Index to his Past History.' London, 18 95. JLIN .1 PRI11IATE 19 tral form, from a hypothetical 'Archi- primas. (2) The Lemures are the older and lower of the natural groups of the Primates; they stand between the oldest Placentalia (Prochoriata) and the true Simiæ. (3) All the Catarrhinæ, or Eastern Simiæ, forD1 one natural monophyletic group. Their hypo- thetical common ancestor, the Archipithecus, Inay have descended directly or indirectly from a branch of the Lemures. (4) Man is descended directly from one series of extinct Catarrhine ancestors. The n10re recent ancestors of this series were tailless anthropoids (similar to the Anthropopi- thecus), with five sacral vertebræ. The more remote ancestors were tailed Cercopi- theci, with three or four sacral vertebræ. These four theses possess, in n1Y opinion, absolute certainty. They are independent of all future anatomical, en1bryological, and palæontological discoveries which ll1ay pos- sibly throw more lignt upon the details of our phyletic anthropogenesis. 2 2 II. TIlE next question is, how the facts of palæontology agree with these n10st in1portant results of cOlnparative anaton1Y and ontogeny. The fossils are the true historical 'medals of creation,' the palpable evidence of the his- torical succession of all those innun1erable organic forms which have peopled the globe for n1any millions of years. Here the question arises, If the known fossil specimens of l'vlam- n1alia, and particularly of Prin1ates, give proof of these Pithecometra-theses, do they con- firm directly the descent of 111an from ape- like creatures? The answer to this question is, in n1Y opinion, affinl1ati ve. I t is true that the gaps in the palæonto- logical evidence, here as elsewhere, are 20 FOSSIL PRIlIIATES 21 many and keenly felt. In the order of the Primates they are greater than in many other orders, chiefly because of the arboreal life of our ancestors. The explanation is very silnple. I t is really due to a long chain of favourable coincidences if the skeleton of a vertebrate, covered as it was with flesh and skin, and containing still more perishable viscera, is petrified at all. The body l11ay be devoured by other creatures, and its bones scattered about; or it rots away and crun1bles to pieces. lVlany animals hide in thick under- gro\\t.th when death approaches them; and, leading an almost entirely arboreal life, the Prinlates are especially likely to disappear without being fossilized. I t is only wh.en the body is quickly covered with sand, or is enl- bedded in suitable lin1e or silica containing n1ud, that the process of petrifaction can con1e to pass. Even then it is only by great o-ood luck that we corne across such a fossil. b Very few countries have been searched systernatically, and the areas that have been 22 THE L..lST LIl'lA searched amount to little in comparison \\yith the whole surface of the land, even if we lea ve out of account the fact that more than two-thirds of the globe are covered by water. These deplorable deficiencies of elnpirical palæontology are balanced on the other side by a growing number of positive facts, which possess an inestimable value in human phylogeny. The most interesting and most in1portant of these is the celebrated fossil Pithecanthroþus ereetus, discovered in Java in 1894 by Dr. Eugène Dubois.* Three years ago this now famous ape-like man provoked an animated discussion at the third I nternational Zoological Congress at Leyden. I Inay. therefore be allo\\tyed to say a few words as to its scientific significance. U n- fortunately, the fossil remains of this creature are very scanty: the skull-cap, a fen1ur, and two teeth. I t is obviously in1possible to forn1 * Pitheca71throþlls erer/us. ' Eine Inenschenähnliche Uebergangsform aus Java' (' A IIuman-like Transitional Form '). Bata\'ia, 1894. FOSSIL PRIivIATES 23 from these scanty remains a complete and satisfactory reconstruction of this remarkable Pliocene Primate. The more in1portant points are the follow- ing: The remains in question rested upon a conglomerate which lies upon a bed of marine marl and sand of Pliocene age. l'ogether with the bones of Pithecanthropus were found those of Stegodon, Leptobos, Rhinoceros, Sus, Felis, H yæna, Hippopotamus, r[apir, Elephas, and a gigantic Pangolin. I t is remarkable that the first two of these genera are now extinct, and that neither hippopotatnus nor hyæna exists any longer in the ()riental region. If we may judge fron1 these fossil ren1ains, the bones of Pithecanthropus are not younger than the oldest Pleistocene, and probably belong to the upper Pliocene. The teeth are like those of Inan. The femur, also, is very human, but shows some resen1blances to that of the gibbons. I ts size, however, indicates an animal which- stood when erect not less than 5 feet 6 inches high. The 24 THE LAST LINK skull-cap also is very human, but with very prominent eyebrow ridges, like those of the famous Neanderthal cranlun1. I t IS certainly not that of an idiot. I t had an estin1ated cranial capacity of about 1,000 cubic centin1etres-that IS to say, lTIuch n10re than that of the largest ape, which possesses not n10re than 600 c.c. The crania of female A ustralians and Veddahs measure not more than I, 100, some even less than 1,000 c.c. ; but, as these Veddah women stand only about 4 feet 9 inches high, the con1puted cranial capacity of the lTIuch taller Pithecan- thropus is comparatively very low indeed. * The final result of the long discussion at Leyden was that, of twelve experts present, three held that the fossil remains belonged to a low race of man; three declared then1 to be those of a n1an-like ape of great size; * On the day after the delivery of this address Dr. Dubois exhibited the cranium of Pithecanthropus, fron1 which he had removed the stony matrix which filled the inside, in order to examine the impression l.eft by the cerebral convolutions. He was able to show that they also are very human, and more highly developed than those of the recent apes. Cro -Þfagnoll/ .-...------------ "" Ñealldprthaú " ..... ...... . , .... -t- J .... 0 .,. .. , iii. r L t "L, u.s " " IF · C()., "II . I If 1 ," t }t e. . .. " IC l v · I Ja I " . , b ChO Il , .. t,LfL , ...fV 't- }.-' '.. I,. t- .,. ., , l' , l' , .. , .. \ '" , ... .... .. . or I< ...... -,.. · .. t- ...,. .... ....... The upper figure represents the outlines of the skuIl of Pithecan- thropus, as restored by l\lanouvier. '. The lower figure shows the comparative size and shape of Pithecanthropus, the Neanderthal skull, a specimen of the Cra-Magnon race of neolithic France, and a Young Chimpanzee before the full development of the supraorbital crests. * L. Manouvier: 'Deuxièllle étude sur Ie Pithecanthropus erect us comllle précurseur présumé de I'homme.' (Hlllletins de la SOl. d'A nthropolo,E:ie de Paris, 1895.) 26 THE LAST LIf\/K the rest maintained that they belonged to an intermediate form, which directly connected primitive man with the anthropoid apes. This last view is the right one, and accords with the laws of logical inference. Pithe- canthroþus e1"'ectus of Dubois is truly a Pliocene remainder of that famous group of highest Catarrhines which were the immediate pithecoid ancestors of n1an. He is, indeed, the long-searched-for ' missing link,' for which, in 1866, I myself had proposed the hypothetical genus Pithecanthropus, species Alalus. I t must, however, be admitted that this opinion is still strongly combated by some distinguished authorities. At the I....eyden congress it was attacked by the illustrious pathologist Rudolf Virchow. * He, however, is one of the minority of leading men of science who set themselves to refute the theory of Evolution in every possible way. F or thirty years he has defended the thesis: , I t is quite certain that n1an is not a * See Notes, p. 93. FOSSIL PRI1}IA TES 27 descendant of apes.' He declares any inter- mediate form to be unin1aginable save in a dream. Virchow went to the Leyden Congress \yith the set purpose of disproving that the bones found by Dubois belonged to a creature which linked together apes and man. First, he maintained that the skull was that of an ape, while the thigh belonged to man. This insinuation was at once refuted by the expert palæontologists, who declared that without the slightest doubt the bones belonged to one and the same individual. Next, Virchow eXplained that certain exostoses or growths observable on the thigh proved its human nature, since only under careful treatment the patient could have healed the original injury. Thereupon Professor 1\1arsh, the celebrated palæontologist, exhibited a nU111ber of thigh-bones of wild monkeys which showed similar exostoses and had healed without hospital treatment. As a last argu- n1ent the Berlin pathologist declared that 28 TIlE LAST LINK the deep constriction behind the upper margin of the orbits proved that the skull was that of an ape, as such never occurred in man. I t so happened that a few weeks later Professor Nehring of Berlin den10nstrated exactly the same formation on a human pre- historic skull received by him frotn Santos, in Brazil. Virchow was, in fact, just as unlucky in Leyden in his fight with our pliocene ancestor as he had been unfortunate in his opinion on the famous skulls of Neanderthal, Spy, La N aulette, etc., everyone of \vhich he eXplained as a pathological abnorma1ity. It would be a very curious coincidence indeed if all these and other fossil hun1an ren1ains were those of idiots or otherwise abnormal indi viduals, provided they are old and lovv enough in their organization to be of phylo- genetic value to the unbiassed zoologist. As the sworn adversary of Evolution, transforn1isn1, and Darwinisn1 in particular, but a believer in the constancy of species, the FOSSIL PRllJIATES 29 great and renowned pathologist has been drh en to the incredible contention that all variations of organic fornls are pathological. F our years ago, as honorary president of the Anthropological Congress at Vienna, he attacked Darwinism in the severest nlanner, and declared that 'man may be as well descended from the elephant or fron1 the sheep as fronl the ape.' Such attacks on the theory of transformism indicate a failure to understand the principles of the theory of Evolution and to appreciate the significance of palæontology, comparative anatomy, and on togen y. The thousands of other objections which have been made during the last forty years (chiefly by outsiders) may be passed over in silence. They do not require serious refuta- tion. In spite of, or perhaps because of, these attacks, the theory of Evolution stands established more firmly than ever. I t is easy for the outsider to exult over the difficulties which our problem implies- diffi- 3 0 THE LASE LINK culties which we who have given our lives to the study understand likewise, and try our best not only to bridge over, but also to point out. Anyhow, we do not conceal them; while those who reject the explanation offered by Evolution make the most of the gaps, and pass silently over the far more nun1erous points favourable to our theory. How fruitful during the last thirty years the astonishing progress in our palæonto- logical knowledge has been for our Pithe- cOllletra-thesis is best shown by a short glance at the growth of our knowledge of fossil Prin1ates. Cuvier, * the founder of palæonto- logy, continued up to the time of his death, in 1832, to assert that fossil remains of monkeys and lemurs did not exist. rrhe only skull of a fossil lemuroid which he de- scribed (namely, Adapis) he declared to be that of an ungulate. Not until 1836 were the first fragments of extinct monkeys found in India; it was two years later, near Athens, * See notes, p. 87. FOSSIL PRI.JLIIES 3 1 that the skeleton of A-Iesoþithecus þentheliclts was discovered. Other remains of lemurs were found in 1862. But during the last t\venty years the number of fossil Primates has been augmented by the remarkable dis- coveries of Gaudry, Filhol, Milne Edwards, Seeley, Schlosser, and others in Europe; of l\Iarsh, Cope, Osborn, Leidy, Aineghino, In South America; and Forsyth Major In IVI adagascar."* These tertiary remains, chiefly * F. AI\IEGHINO: 'Contribucion al conocimiento de los mamíferos de la república Argentina.' In A das de la Academia 7laciollal de Scie7zcÙls ell Cordoba, 1889.-Another article in Revista A rgelltillll de His- torill natural. Buenos Aires, 1891. A. GAUDRY: 'Animaux fossiles et géologie de l'Attique.' 1862.-' Le Dryopithèque.' Mém. Soc. géol. de .l'rall{e : 'Paléontologie.' 1890. O. l\IARSH: 'Introduction and Succession of Vertebrate Life in America.' Address, Amer. Assoc. Ad v. Sci., Nashville, 1887. H. F. OSBORN: 'The Rise of the Iamma]ia in North America.' Address, AlTIer. Assoc. Adv. Sci., l\1adi- son, 1893. L. RUETII\IEYER : 'Ueber die Herkunft unserer Thierwelt,' Basel, 1867. C. S. FORSYTH MAJOR: 'Fossil Monkeys from l\Iadagas- car.' Geological bf agll Ùze, 1896. :\1. SCHLOSSER: 'U eher die Beziehungen der ausgestorbenen Saeugethielfaunen und ihr VerhaeILni s zur Saeuge- thierfauna der Gegenwart.' Diolog. Centralblatt, 1888. ....., .)- THE LAST LliVR of Eocene and IVI iocene date, fill many gaps between existing genera of Primates, and afford us quite a clear insight into the phy- letic developn1ent of this order during the millions of years of the Cænozoic age. The most in1portant difference between the two groups of existing monkeys is indicated by their dentition. Adult man possesses, like all the other Catarrhine Simiæ, thirty-two teeth, whilst the American monkeys (the Platyrrhinæ) have thirty-six teeth--namely, one pair of premolars more in the upper and lower jaws. Comparative odontology leads us to the phylogenetic conclusion that this number has been produced by reduction from a still older form with forty-four teeth. 1'his typical dental formula (three incisors, one canine, four premolars, and three molars, in each half-jaw) is common to all those n10st important older mammals which in the begin- ning of the Eocene period constituted the four large groups of Lemuravida, Condylarthra, Esthonychida, and I ctopsida. These are the FOSSIL PRIJIATES "... J.J four ancestral groups of the four main orders of Placenta1ia - namely, of the Primates, V ngu]ata, Rodentia, and Carnassia. They seem to be so closely related by their primi- tive organization that they may be united in one common super-order, Prochoriata. With a considerable degree of proba- bility, we are led to formulate the further hypothesis that all the orders of Placentalia -from the lowest Prochoriata upwards to man-have descended from some unknown common ancestor living in the Cretaceous period, and that this oldest placental form originated from some Jurassic group of marsupials. Among these numerous fossil Lemures which have been discovered within the last twen ty years, there exist, indeed, all the con- necting forms of the older series of Primates, all the 'missing links' sought for by com- parative odontology. The oldest Lemures of the tertiary age are the Eocene Pachylemures, or Hyopso- ..., ..) 3-+ THE L..1ST LINK dlna. They possess the complete dentition of the Prochoriata-namely, forty-four teeth ( 3. _ 1 .4.3 _ ). Th 11 h E I - en fo ow t e ocene Pa æo- 3.1.4.3 lemures, or Adapida, with forty teeth, they having lost one pair of incisors in each jaw. To these are attached the younger Auto- lemures, or Stenopida, with thirty-six teeth, they thus possessing already the same den- tition as the Platyrrhinæ. The characteristic dentition of the Catarrhinæ is derived from this formula by the loss of another premolar. These relations are so clear and so closely connected with a gradual transformation of the whole skull, and with the progressive differentiation of the Primate-form, that we are justified in saying that the pedigree of the Primates, from the oldest Eocene Lemures upwards to man, is n