Page Two 



EVOLUTION 



January, 1929 



The Origin of Man from the Anthropoid Stem 



When and Where? 



{From Bicentenary Number of American Philosophical Society's Proceedings, Vol. LXI'I, 1927) 



By WILLIAM K. GREGORY 



PROFESSOR OSBORN has recently argued that for 

 more than one million years past our ancestors have 

 been erect-walking, large-brained, speaking men, not dif- 

 fering in essentials from the human genus of to-day and 

 contrasting profoundly with the arboreal or semi-arboreal 

 great apes. 



This immense vista of man's antiquity and of his aloof- 

 ness from other mammals has called forth more than one 

 expression of thankfulness that the much maligned human 

 race has at last been freed by anthropological science 

 from a degrading sense of kinship with apes and monkeys 

 — repulsive creatures whose very names in ancient and 

 modern times have been used in contempt and derision. 

 This bar sinister in man's reputed pedigree has been 

 viewed with horror by many anti-evolutionists, who have 

 sought by every artifice of rhetoric to discredit the idea; 

 but scientists of world-wide reputation have also striven 

 either to secure a verdict of "not proven" or to establish 

 a complete alibi for mankind. 



And now Professor Osborn hands down a decision at 

 first sight quite adverse to the claims of the anthropoid 

 tribe to the place of honor as man's next of kin. Specific- 

 ally, he holds that these animals "constitute a separate 

 branch of the great division of primates, not only inferior 

 to the HominidjE but totally disconnected from the human 

 family from its earliest infancy." 



But, like the slave in the classical story whose unpleas- 

 ant and doubtless risky duty it was to remind royalty 

 "Memento te hominem esse." I conceive it as my hard 

 duty to remind mankind that these poor relations of ours, 

 mute witnesses of the past, are still with us and that the 

 evidence of our lowly origin can hardly be waved aside 

 on the ground of the length and aloofness of our own 

 lineage. 



If we concentrate our attention on the evidence for the, 

 at first, almost inconceivable antiquity of man as an inde- 

 pendent family, we may easily forget that the Pliocene 

 epoch is next to the nearest to us of a long line of known 

 geologic epochs, most of which are many times longer 

 than the Pliocene itself. If we accept Barrell's estimates 

 based on the rate of disintegration of uranium into lead 

 and helium, we find that even the Lower Pliocene is only 

 some six million years distant from us, while the begin- 

 ning of the Eocene is set down as some sixty million years 

 ago. And what is this in turn, compared with the 700 

 millions of years since the beginning of the Palaeozoic? 

 At most, the human race has then been proved to be a 

 superior line of its own for less than one hundredth part 

 of the time that bivalve molluscs have been separate from 

 univalves or sponges from corals. 



Man is not the only mammal of the Pliocene epoch that 

 was already substantially like his modern representatives. 

 Palaeontologists have shown that the same is true of the 



horses, tapirs, rhinoceroses, elephants, bears, pigs, mon- 

 keys, apes and many other mammals. In other words, 

 the amount of evolution that has apparently taken place 

 since Pliocene times in all these groups appears at first 

 sight to be surprisingly slight. 



However, if the geologic epochs themselves extend as 

 many millions of years as they are supposed to do, is it 

 any wonder that the old "phylogenetic trees" have been 

 lengthened into clusters of nearly parallel lines, converg- 

 ing only at extremely distant points? But because horses 

 and asses may have been on separate lines far longer than 

 was formerly thought are they in reality any less nearly 

 related to each other than they were before? And in 

 general are zoological relationships, e.g. of the horse to 

 the rhinoceros and the tapir, really altered because our 

 ideas of the antiquity in years of all creatures has been 

 greatly expanded ? 



Partly because the amount of evolution since Pliocene 

 times appears at first sight to have been very slight and 

 because evolution in the horses, proboscideans, and many 

 other families has usually been extremely slow through- 

 out the Tertiary period, it might be suspected that evo- 

 lution in man has been equally slow and that man will be 

 proved to be distinct from other families as far back as 

 the families of horses, rhinoceroses, proboscideans, etc., 

 vv-ere separate from each other; that is, as far back as at 

 least the Eocene epoch. 



However, primitive horses, with undiminished side toes 

 and short-crowned teeth, in general characteristic of the 

 Oligocene epoch, persist in the Miocene, side by side with 

 more progressive families with reduced side toes and 

 long-crowned teeth, leading to modern horses. So, too, 

 it is generally recognized that certain groups have changed 

 but little during enormous reaches of geologic time, while 

 others have become profoundly specialized during the same 

 period. Among the mammals, the opossum has come 

 down to us with only slight modifications in the dentition 

 from the primitive marsupials of the Upper Cretaceous. 

 The family of horses, on the other hand, during the same 

 period underwent intensive modifications. In view of 

 all this, where is the direct evidence that the evolution of 

 man has proceeded at approximately the same average rate 

 as that of the horse and his congeners, and that the two 

 families date back equally far in geologic time? 



Before taking up the direct palaeontological evidence 

 on this matter, let us consider several lines of indirect 

 evidence. 



If man and ape had parted company as long ago as did 

 tapir and horse, their relatively higher instability should 

 have made their molar patterns far more different from 

 each other than those of tapir and horse, whereas the con- 

 trary is the fact. This assuredly adds weight to the 

 argument that the kinship of man to the chimpanzee is 



