84 THE DESCENT OF MAN. Part I. 



preservation. Nevertheless trie migratory instinct is so 

 powerful that late in the autumn swallows and house- 

 martins frequently desert their tender young, leaving 

 them to perish miserably in their nests. 18 



We can perceive that an instinctive impulse, if it be in 

 any way more beneficial to a species than some other or 

 opposed instinct, would be rendered the more potent of 

 the two through natural selection ; for the individuals 

 which had it most strongly developed would survive in 

 larger numbers. Whether this is the case with the 

 migratory in comparison with the maternal instinct, 

 may well be doubted. The great persistence or steady 

 action of the former at certain seasons of the year 

 during the whole day, may give it for a time para- 

 mount force. 



Man a social animal. — Most persons admit that man 

 is a social being. We see this in his dislike of solitude, 

 and in his wish for society beyond that of his own 

 family. Solitary confinement is one of the severest 

 punishments which can be inflicted. Some authors sup- 

 pose that man primevally lived in single families ; but 

 at the present day, though single families, or only two 

 or three together, roam the solitudes of some savage 

 lands, they are always, as far as I can discover, friendly 

 with other families inhabiting the same district. Such 

 families occasionally meet in council, and they unite 



18 This fact, the Eev. L. Jenyns states (see his edition of ' White's 

 Nat. Hist, of Selborne,' 1853, p. 204) was first recorded by the illus- 

 trious Jenner, in ' Phil. Transact.' 1824, and has since been confirmed 

 by several observers, especially by Mr. Blackwall. This latter careful 

 observer examined, late in the autumn, during two years, thirty-six 

 nests ; he found that twelve contained young dead birds, five contained 

 eggs on the point of being hatched, and three eggs not nearly hatched. 

 Many birds not yet old enough for a prolonged flight are likewise 

 deserted and left behind. See Blackwall, 'Researches in Zoology,' 

 1834, pp. 108, 118. For some additional evidence, although this is nut 

 wanted, see Leroy, 4 Lettres Phil.' 1802, p. 217. 



