202 Changing Human Nature 



in the teeth. Thus, the Propliopithecus of the Egyptian 

 Eocene has a molar tooth pattern that might have led as 

 readily to the anthropoid as to the human type. During 

 the following fifteen million years there was an increasing 

 number of anthropoid forms characterized by the same basic 

 tooth pattern as that found both in anthropoids and in man. 

 The forest ape Dryopithecus, which became dominant in 

 Miocene times, was an animal about the size of the modern 

 chimpanzee. It had powerful canine teeth resembling those 

 of modern apes. On the other hand, the molar teeth were 

 remarkably like modern human molars, while the chin was 

 also more like man's than like the modern chimpanzee's or 

 gorilla's. It is on such facts as these that Professor 

 W. K. Gregory rests the theory that Dryopilhecus, or a 

 close relative of this type, was the common ancestor of 

 modern anthropoids and of man, although President 

 Henry Fairfield Osborn would expect to find a com- 

 mon ancestor in a more primitive type of a much earlier 

 period. 



At the present time the divergence between the Old 

 World monkeys and the New World monkeys, between the 

 monkeys and the apes, between the apes and man, are so 

 great that they indicate a very rapid change in type during 

 the sixty to one hundred million years that have elapsed 

 since the most primitive primates made their first appearance. 

 This end result of wide divergence is significantly related by 

 Professor Gregory to the exceptional variability of all 

 human and anthropoid material which has been studied. 

 That is to say, out of a given number of specimens of such 

 material, there is more difference between extreme measure- 

 ments or proportions than is found in a corresponding lot of 

 material representing other orders of vertebrates, let us say 

 the ungulates or the carnivora. This greater variability would 

 mean more rapid modification of forms, no matter what 

 theory we may adopt as to the actual mechanism by which 

 change of type has been brought about. 



