THE DESCENT OR OBIGIN OF MAN 139 



many little services for each other; horses nibble, and 

 cows lick each other, on any spot which itches; monkeys 

 search each other for external parasites ; and Brehm states 

 that after a troop of the Cercopithecus griseo-viridis has rushed 

 through a thorny brake, each monkey stretches itself on a 

 branch, and another monkey sitting by, "conscientiously" 

 examines its fur, and extracts every thorn or bur. 



Animals also render more important services to one 

 another; thus wolves and some other beasts of prey hunt 

 in packs, and aid one another in attacking their victims. 

 Pelicans fish in concert. The Hamadryas baboons turn 

 over stones to find insects, etc. ; and when they come to a 

 large one, as many as can stand round turn it over together 

 and share the booty. Social animals mutually defend each 

 other. Bull bisons in North America, when there is danger, 

 drive the cows and calves into the middle of the herd, while 

 they defend the outside. I shall also in a future chapter 

 give an account of two young wild bulls at Chillingham at- 

 tacking an old one in concert, and of two stallions together 

 trying to drive away a third staHion from a troop of mares. 

 In Abyssinia, Brehm encountered a great troop of baboons, 

 who were crossing a valley: some had already ascended the 

 opposite mountain, and some were still in the valley: the 

 latter were attacked by the dogs, but the old males immedi- 

 ately hurried down from the rocks, and with mouths widely 

 opened, roared so fearfully that the dogs quickly drew 

 back. They were again encouraged to the attack; but by 

 this time ^11 the baboons had reascended the heights, ex- 

 cepting a young one, about six months old, who, loudly 

 calling for aid, climbed on a block of rock, and was sur- 

 rounded. Now one of the largest males, a true hero, came 

 down again from the mountain, slowly went to the young 

 one, coaxed him, and triumphantly led him away — the dogs 

 being too much astonished to make an attack. I cannot 

 resist giving another scene which was witnessed by this 

 same naturalist: An eagle seized a young Cercopithecus, 

 which, by clinging to a branch, was not at once carried oflE; 



