THE HISTORY OF THE PRIMATES 



Africa. These most nearly resemble man in structure of skull and skeleton, 

 dentition, physiology, blood groups, parasitic susceptibilities, and other 

 characteristics. They are, however, highly specialized for an arboreal 

 mode of life. Their arms are greatly elongated, and they swing through 

 the trees by a method called brachiation, that is, they swing from branch 

 to branch with their arms alone, their bodies and legs playing only an 

 indirect role. The thumbs have accordingly become reduced, so that the 

 hand can function largely as a hook in grasping branches. The legs are 

 much shorter than the arms, in contrast to the Old World monkeys and man. 



The gibbon is the smallest of the anthropoid apes, and in many respects 

 it is the most primitive. It is completely arboreal, and, while it is capable 

 of remarkably swift and accurate brachiation, it is more adroit on foot 

 than most of the apes, for it can run along the branches quite skillfully. 

 The siamang is closely related to the gibbon, and differs from it only in 

 details. The orangutan is a much larger ape, often weighing well over 

 100 pounds, but it is still primarily arboreal, and moves quite successfully 

 by brachiation. It rarely descends to the ground. The chimpanzee is some- 

 what larger and is arboreal. The gorilla is much the largest of the apes, 

 reaching weights in excess of 600 pounds. Although gorillas are brachi- 

 ators morphologically, the huge size of the adults confines them to the 

 ground, where they use a peculiar type of quadripedal locomotion. 



Summary of Classification. This, then, is the array of organisms which 

 makes up the order Primates, of which man is the dominant member. In 

 the most recent taxonomic revision of the mammals, the Primates are 

 divided into two suborders, the Prosimii, including tree shrews, lemurs, 

 and tarsiers; and the Anthropoidea, including monkeys, the anthropoid 

 apes, and man. The Anthropoidea are further subdivided into three super- 

 families, the Ceboidea, including the platyrrhine monkeys; the Cerco- 

 pithecoidea, or catarrhine monkeys; and the Hominoidea, including man 

 and the anthropoid (man-like) apes. The Hominoidea is divided into two 

 families, the Hominidae including only man, and the Pongidae including 

 all of the anthropoid apes. 



Each group of Primates discussed above shows some significant ad- 

 vances over the one preceding it, and there is a temptation to treat them 

 as an evolutionary series, as has been done in the past. Yet a little reflec- 

 tion will make it clear that each of these groups is the more or less spe- 

 cialized end product of a long evolution of its own, and the living tree 

 shrews, for example, could hardly be ancestral to the lemurs. But very 

 primitive ancestors of the tree shrews of today may well have been an- 

 cestral also to the lemurs. It is important to bear this in mind, for there 

 used to be much argument over which of the living apes was the pro- 

 genitor of man, and this viewpoint has been revived in a recent book. But 

 most authorities now regard the question as quite absurd. 



PROSIMIANS IN THE FOSSIL RECORD 



The paleontological record of the Primates is very incomplete but it is 

 ancient, for primate remains have been found from rocks of mid-Paleocene 



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