138 THE DESCENT OF MAN 



and the other ought not; the one would have been right, and 

 the other wrong; but to these terms I shall recur. 



Sociability. — Animals of many kinds are social; we find 

 even distinct species living together; for example, some 

 American monkeys; and united flocks of rooks, jackdaws, 

 and starlings. Man shows the same feeling in his strong 

 love for the dog, which the dog returns with interest. 

 Every one must have noticed how miserable horses, dogs, 

 sheep, etc., are when separated from their companions, 

 and what strong mutual affection the two former kinds, at 

 least, show on their reunion. It is curious to speculate 

 on the feelings of a dog, who will rest peacefully for hours 

 in a room with his master or any of the family, without the 

 least notice being taken of him; but if left for a short time 

 by himself, barks or howls dismally. We will confine our 

 attention to the higher social animals ; and pass over insects, 

 although some of these are social, and aid one another in 

 many important ways. The most common mutual service 

 in the higher animals is to warn one another of danger by 

 means of the united senses of all. Every sportsman knows, 

 as Dr. Jaeger remarks,' how difficult it is to approach ani- 

 mals in a herd or troop. "Wild horses and cattle do not, 1 

 believe, make any danger-signal; but the attitude of any 

 one of them who first discovers an enemy warns the others. 

 Babbits stamp loudly on the ground with their hind feet as 

 a signal ; sheep and chamois do the same with their forefeet, 

 uttering likewise a whistle. Many birds, and some mam- 

 mals, post sentinels, which in the case of seals are said' 

 generally to be the females. The leader of a troop of 

 monkeys acts as the sentinel, and utters cries expressive 

 both of danger and of safety.' Social animals perform 



' "Die Darwin'sche Theorie," s. 101. 



8 Mr. B. Brown in "Proc. Zoolog. Soc," 1868, p. 409. 



» Brehm, "Thierleben," B. i., 1864, s. 52, 19. For the case of the monlieys 

 extracting thorns from each other, see s. 54. "With respect to the Hamadryas 

 turning over stones, the fact is given (s. 76) on the evidence of Alvarez, whose 

 observations Brehm thinks quite trustworthy. For the cases of the old male 

 Imboons attacking the dogs, see s. 79 ; and with respect to the eagle, 8. 66L 



