Man and Monkeys 133 



pentadactylous Eocene forms, which may either have led directly 

 to the evolution of man (AdlofF), or have given rise to an ancestral 

 form common to apes and men (Klaatsch 1 , Giuffrida-Ruggeri). The 

 common ancestral form, from which man and apes are thus supposed 

 to have arisen independently, may explain the numerous resemblances 

 which actually exist between them. That is to say, all the characters 

 upon which the great structural resemblance between apes and 

 man depends must have been present in their common ancestor. 

 Let us take an example of such a common character. The bony 

 external ear-passage is in general as highly developed in the lower 

 Eastern monkeys and the anthropoid apes as in man. This character 

 must, therefore, have already been present in the common primitive 

 form. In that case it is not easy to understand why the Western 

 monkeys have not also inherited the character, instead of possessing 

 only a tympanic ring. But it becomes more intelligible if we assume 

 that forms with a primitive tympanic ring were the original type, and 

 that from these were evolved, on the one hand, the existing New 

 World monkeys with persistent tympanic ring, and on the other an 

 ancestral form common to the lower Old World monkeys, the anthro- 

 poid apes and man. For man shares with these the character in 

 question, and it is also one of the "unimportant" characters required 

 by Darwin. Thus we have two divergent lines arising from the 

 ancestral form, the Western monkeys (Platyrrhine) on the one hand, 

 and an ancestral form common to the lower Eastern monkeys, the 

 anthropoid apes, and man, on the other. But considerations similar 

 to those which showed it to be impossible that man should have 

 developed from an ancestor common to him and the monkeys, yet 

 outside of and parallel with these, may be urged also against the 

 likelihood of a parallel evolution of the lower Eastern monkeys, the 

 anthropoid apes, and man. The anthropoid apes have in common 

 with man many characters which are not present in the lower Old 

 World monkeys. These characters must therefore have been present 

 in the ancestral form common to the three groups. But here, again, 

 it is difficult to understand why the lower Eastern monkeys should 

 not also have inherited these characters. As this is not the case, 

 there remains no alternative but to assume divergent evolution from 

 an indifferent form. The lower Eastern monkeys are carrying on 

 the evolution in one direction — I might almost say towards a blind 

 alley — while anthropoids and men have struck out a progressive 

 path, at first in common, which explains the many points of re- 

 semblance between them, without regarding man as derived directly 

 from the anthropoids. Their many striking points of agreement 



1 Klaatsch in his last publications speaks in the main only of an anceritral form 

 common to men and anthropoid apes. 



