Chap. VII. The Extinction of Races. 1 89 



inter-breeding ; but in the above cases infertility has coincided 

 too closely with the arrival of Europeans for us to admit this 

 explanation. Nor have we at present any reason to believe 

 that man is highly sensitive to the evil effects of inter-breeding., 

 especially in areas so large as New Zealand, and the Sandwich 

 archipelago with its diversified stations. On the contrary, it is 

 known that the present inhabitants of Norfolk Island are nearly 

 all cousins or near relations, as are the Todas in India, and the 

 inhabitants of some of the Western Islands of Scotland; and 

 yet they seem not to have suffered in fertility. 45 



A much more probable view is suggested by the analogy of 

 the lower animals. The reproductive system can be shewn to be 

 susceptible to an extraordinary degree (though why we know 

 not) to changed conditions of life ; and this susceptibility leads 

 both to beneficial and to evil results. A large collection of facts 

 on this subject is given in chap, xviii. of vol. ii. of my ' Variation 

 of Animals and Plants under Domestication/ I can here give only 

 the briefest abstract ; and every one interested in the subject 

 may consult the above work. Very slight changes increase the 

 health, vigour and fertility of most or all organic beings, 

 whilst other changes are known to render a large number of 

 animals sterile. One of the most familiar cases, is that of tamed 

 elephants not breeding in India; though they often breed in 

 Ava, where the females are allowed to roam about the forests to 

 some extent, and are thus placed under more natural conditions. 

 The case of various American monkeys, both sexes of which 

 have been kept for many years together in their own countries, 

 and yet have very rarely or never bred, is a more apposite in- 

 stance, because of their relationship to man. It is remarkable 

 how slight a change 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. 46 Certain 

 groups of animals are much more |iable 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, whilst the others are not 

 so ; on the other hand, a single species may retain its fertility 



45 On the close relationship of the Scotland, Dr. Mitchell, 'Edinburgh 



Norfolk Islanders, see Sir \V. Deni- Medical Journal,' March to June, 



son, 'Varieties of Vice-Regal Lite,' 18G5. 



vol. i. 1870, p. 410. For the Todas, ia For the evidence on this head, 



»e« Col. Marshall's work, 1873, p. see 'Variation of Animals' &c, 



110. For the Western Islands of vol ii. p. 111. 



