216 THE DESCENT OF MAN. 



in the conditions often induces sterility in a wild animal 

 when captured; and this is the more strange as all our 

 domesticated animals have become more fertile than they 

 were in a state of nature; and some of them can resist the 

 most unnatural conditions with undiminished fertility.* 

 Certain groups of animals are much more liable than others 

 to be affected by captivity; and generally all the species of 

 the same group are affected in the same manner. But 

 sometimes a single species in a group is rendered sterile^ 

 while the others are not so; on the other hand,, a single 

 species may retain its fertility while most of the others fail 

 to breed. "The males and females of some species when 

 con fined, or when allowed to live almost but not quite free, 

 in their native country never unite; others thus circum- 

 stanced frequently unite but never produce offspring; 

 others again produce some offspring, but fewer than in a 

 state of nature; and as bearing on the above cases of man 

 it is important to remark that the young are apt to be 

 weak and sickly, or malformed, and to perish at an early 

 age. 



Seeing how general is this law of the susceptibility of the 

 reproductive system to changed conditions of life, and that 

 it holds good with our nearest allies, the Quadrumana, I 

 can hardly doubt that it applies to man in his primeval state. 

 Hence, if savages of any race are induced suddenly to change 

 their habits of life they become more or less sterile, and 

 their young offspring suffer in health in the same manner 

 and from the same cause as do the elephant and hunting- 

 leopard in India, many monkeys in America, and a host 

 of animals of all kinds on removal from their natural 

 conditions. 



We can see why it is that aborigines, who have long 

 inhabited islands, and who must have been long exposed to 

 nearly uniform conditions, should be specially affected by 

 any change in their habits, as seems to be the case. Civil- 

 ized races can certainly resist changes of all kinds far 

 better than savages ; and in this respect they resemble 

 domesticated animals, for though the latter sometimes 

 suffer in health (for instance European dogs in India), yet 

 they are rarely rendered sterile, though a few such 



*For the evidence on this head, see " Variation of Animals," etc., 

 vol. ii, p. 111. 



