MAN'S RELATIVES: THE PRIMATES 



477 



platyrrhines by the shape of the nose, the lack of a prehensile tail, and 

 the presence on the buttocks of bare callous areas which are often bril- 

 liantly colored, especially in the males. There are two groups, one of 

 which includes plant-feeding arboreal monkeys in which the thumb has 

 become vestigial, the hind legs are longer than the front ones, cheek 

 pouches are lacking, and the stomach has become large and complicated, 

 as in animals that chew their cud. 

 Most of the Old World monkeys, 

 however, belong to the other group 

 in which the thumb is well devel- 

 oped, the front legs are at least as 

 long as the hind ones, there are 

 cheek pouches for holding food, and 

 the stomach is simple. Many mem- 

 bers of this second group, such 

 as the guenons and mangabeys, 

 are typical tree-dwelling monkeys. 

 Others — the mandrills, drills, and 

 baboons of Arabia and Africa — have 

 taken to the ground. They walk and 

 run as quadrupeds on the palms of 

 the hands and soles of the feet but 

 retain the grasping thumb and big 

 toe. Their muzzles have become 

 elongated and doglike, and the 

 canine teeth are large tusks. The 

 Old World monkeys as a group show 

 many similarities to man, but they 

 have obviously played no part in 

 his evolution and are no more than 

 very distant cousins. 



The manlike apes. Of all ani- 

 mals, the apes of the family Simiidae 

 come closest to man in structure, 

 physiology, and behavior, and the 

 fossil record shows our own ancestry converging with theirs as we go back in 

 time. For this reason we shall take up their evolutionary history in con- 

 nection with that of man and shall here consider only the modern repre- 

 sentatives of this highly interesting group. There are four living types — 

 the gibbon, the orangutan, the chimpanzee, and the gorilla. The gibbon 

 is considerably smaller than man, while the other three types, called the 

 great apes, weigh as much as or considerably more than man. In all of 

 them the skeleton is quite manlike. The chest is broad, in contrast to the 



Fig. 29.7. A male mandrill, one of the large 

 West African baboons of the genus Papio, 

 family Cercopithecidae. These apes have 

 become completely terrestrial and wholly 

 herbivorous. The tooth row is much elon- 

 gated, forming a doglike muzzle armed with 

 large canine tusks (see Fig. 29.8). (Courtesy 

 American Museum of Natural History.) 



