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Show 1 9 0 5 . ] MR. R. I. POCOCK ON A HAINAN GIBBON. 1 7 9 stand third in climbing, third in bipedal and first in quadrupedal powers. Since, therefore, the action of Monkeys, whether Cercopitliecidae, Cebidse, or Hapalidae, and of Lemurs is essentially quadrupedal, the fore and hind limbs being used to an approximately equal extent, both in terrestrial and arboreal locomotion, it may be inferred that the Chimpanzees have departed least in these respects from the primitive Primate stock; the Gorillas a little more in the line of bipedal erection and, concomitantly, loss of climbing power; the Orangs still more in the direction of loss of terrestrial activity and increase of arboreal expertness; the Gibbons most of all in the line of bipedal activity, dexterity in hand-climbing, and loss of quadrupedal power. This serial arrangement of the Apes is the exact opposite of the one prevalent in text-books, where the order adopted is based upon structure with Man placed first as the standard for comparison. It suggests that for the origin of Gibbons we must look not to forms resembling any known Cercopithecoid type, but to forms which had already acquired the Simiine or Antliropo-morphine characteristics and had either lost or never learnt the method and skill in climbing found in the former group. They may have started from a type somewhat on a level with the Chimpanzees with respect to terrestrial and arboreal activity; and to swing with greater facility from tree to tree and to obviate the risk of injury in case of a fall, it is highly probable that they have become dwarfed in stature and grown lighter in build. Their muscularity and length of arm, slightness of body and strength of leg, all factors of importance in enabling them to traverse the jungle and, in case of a miss or a breaking branch, to drop lightly to the ground and run to the nearest tree for safety, were probably perfected concomitantly. That Gibbons are able to drop with safety a considerable distance is substantiated by the fact that Mr. de St. Croix has seen his specimen come to the ground without injury from a height of about 20 feet. When leaping to the ground Gibbons swiftly draw up the knees as the feet touch, exactly as a man does under similar circumstances, to break the shock. Another interesting feature connected with the habits of the Anthropoid Apes is the size of their ears. I have already suggested that the difference in size between the ears of the Orang and those of the Chimpanzee may be connected with the difference of habits of the two animals. The Orang lives a more arboreal and therefore a safer life than the Chimpanzee, which requires quick hearing to enable it to escape to the trees when feeding on the ground*'. Gibbons also, which have relatively large ears, need auditory acuteness for the same purpose as Chimpanzees. This explanation, however, is not complete and appears at first sight to be contradicted by the case of the Gorillas, which have small ears * ‘ Nature,' Oct. 11th, p. 585 (1900). 12* |
