HUMAN HISTOKY 109 



Pleistocene 



3. With man are associated among mammals more or less closely 

 five groups of animals — the Anthropoid apes, the Platyrrhini or 

 Old World monkeys, the Catarrhini or New World monkeys, 

 the Lenmrs, and the Tarsii. It is clear that all these groups 

 diverged from a common stem ; the first divergence, however, 

 must have occurred not later than the Eocene. To ascertain the 

 interrelationship of these groups and the order of their divergence 

 we have to rely chiefly upon the evidence provided by fossils. 

 This evidence is very incomplete and, so far as the definitely 

 pre-human ancestor is concerned, is lacking entirely until we come 

 to a form known as Pithecanthropus, found in Java in a deposit 

 attributed either to the late Pliocene or early Pleistocene. With 

 regard to the evolution of the Primate stock it is usual to assume 

 that the Lemurs ^ and the Tarsii branched off from the main stem 

 very early, and that the Catarrhini followed by the Platyrrhini 

 branched off in the Eocene. It is usual, therefore, to assume 

 that in Oligocene times there was existing a Primate stock 

 ancestral both to the anthropoid apes and to man. It is possible 

 that Propliopithecus from the Fayum is a representative of this 

 common stock from which the gibbons branched off in the 

 Miocene in one direction, and the orang, chimpanzee, gorilla, 

 and man in another. Man, it is imagined, branched off from this 

 latter stock in the early Miocene and the orang shortly after- 

 wards, the separation of the chimpanzee and gorilla occurring 

 somewhat later. Various ancestral gibbons (Pliopithecus and 

 Pliohylobates) and ancestral anthropoids (Dryopithecus, Neo- 

 pithecus, and Palaeopithecus) are known from the Miocene and 

 Pliocene, but nothing has come to light as yet of the distinctively 

 pre-human stock in these times. 



1 The extinct Lemurs of the Lower Eocene were, it may be noticed, of a very 

 generalized type and can only with difficulty be distinguished from Insectivores. 

 At this time the chief features now characteristic of the various Mammalian 

 classes had not yet appeared. 



