478 



THE CHANGING GENERATIONS 



deep chest of monkeys and of mammals in general. The arms are longer 

 than the legs; the hands are quite similar to those of man but with rela- 

 tively longer fingers and shorter thumb ; and the feet are used mostly for 

 walking but are still well fitted for grasping, with the toes long and the 

 big toe opposable and thumblike. The tail is even more rudimentary than 

 in man, and does not project externally. 



These features of the body are related to the mode of locomotion. As 

 the weight increased, the monkeylike four-footed running on a single 

 branch was abandoned in favor of placing the feet on one branch and the 

 hands on a higher one; from this to brachiation was an easy transition. 

 As it swings from the hands, the body necessarily hangs vertical; and 



because the arms are long and the 

 legs are short, an inclined, suberect 

 position of the trunk is maintained 

 even in quadrupedal locomotion on 

 the ground. These are steps in the 

 direction of the erect posture 

 characteristic of man. 



The gibbon. The smallest and 

 most primitive of the manlike apes 

 is the gibbon, of which several kinds 

 inhabit Malaya. This ape averages 

 about 3 feet in height and has extra- 

 ordinarily long arms, which reach to 

 the ground when the animal stands 

 erect. The body is very slender and 

 light, covered with fur rather than 

 with coarse hair like that of the great 

 apes. The skull is low, with prominent brow ridges, a rather flat nose, and 

 protruding jaws; the canine teeth are long tusks; and the hand is long and 

 narrow with a short thumb. Gibbons are the only apes which customarily 

 walk erect, extending the arms to the sides as balancers. They are seldom 

 seen on the ground, however; it is in the trees that they are truly at 

 home. The gibbons have developed brachiation to its highest perfection. 

 They hurl themselves through the air from branch to branch, easily 

 clearing distances of 20 feet, and on occasion making 40-foot leaps. In 

 such progression the feet are doubled up close to the body and the arms 

 are used alternately, taking off with the right, catching momentarily 

 with the left to obtain impetus for a new leap, and so on indefinitely. 

 Brachiation calls for the greatest agility, exact coordination, precise 

 judgment of distance and of strength of branches, sharp eyesight, and 

 general alertness; the penalty for failure is injury or death. 



Fig 29.8. The skull of a baboon in front 

 view, showing the tremendous fighting 

 tusks. {Courtesy American Museum of Nat- 

 ural History.) 



