1 40 EVOLUTION OF THE EARTH 



and hence more active, swinging from tree to tree by the hands 

 with great agility. They rest in the sitting posture, sometimes 

 stand or walk, but run on all fours. Jaws and teeth are their 

 chief defense. 



The gorilla (Fig. 28) is by far the most formidable of all 

 the great apes, for its huge size and strength and its unparal- 

 leled ferocity make it a veritable terror. An authentic re- 

 corded size makes the gorilla five feet one and one-half inches 

 tall and 418 pounds in weight. Its lower limbs, while 

 enormously powerful, are disproportionately short. If the 

 limbs bore a human proportion to the torso, the creatures 

 would stand at least seven feet in height, with a weight of 

 half a thousand pounds! The huge size of this ape has forced 

 it to become partially terrestrial, but instead of becoming 

 more man-like as an adaptation to ground-living, it has taken 

 a yet more brutal aspect, more like a bear than a human being. 



All of these apes, the orang, chimpanzee, and gorilla, are 

 degenerating from the higher condition of their common 

 ancestor with mankind, the chimpanzee least, the gorilla most 

 of all. The gibbons (Fig. 29), however, of which there are 

 several species, while the most remote from mankind in actual 

 relationship, have probably retained in greater degree than 

 any others the habits and development of the anthropoid stem- 

 form. They are wonderful acrobats, their relatively small size 

 and immensely long and powerful arms lending themselves to 

 the full measure of arboreal progression. The gibbons are 

 oriental in distribution, living in the wooded regions of south- 

 eastern Asia and the islands of Sumatra, Borneo, and Java. 



It were well to dwell for a moment upon the locomotive 

 methods of these apes which, instead of running upon the 

 upper side of the branches, as do most arboreal forms, swing 

 beneath them by means of their hands. This method of loco- 

 motion has been called brachiation (Lat. brachium, arm) and 

 in all probability took its rise with the earliest anthropoids, 



