THE RACES OF MAN. 215 



In the paper above quoted, Mr. Macnamara gives veasons 

 for believing that the inhabitants of districts subj.ect to 

 malaria are apt to be sterile; but this cannot apply in sev- 

 eral of the above cases. Some writers have suggested that 

 the aborigines of islands have suffered in fertility and 

 health from long continued 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 sen- 

 sitive to the evil effects of inter-breeding, especially in 

 areas so large as New Zealand and the Sandwich Archi- 

 pelago 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. * 



A much more probable view is suggested by the analogy 

 of the lower animals. The reproductive system can be 

 shown 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- 

 ter xviii, of volume 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, vigor and fertility of most or all organic beings, 

 while 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 mon- 

 keys, 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 instance, because of their 

 relationship to man. It is remarkable how slight a change 



*0n the close relationship of tlie Norfolk Islanders, see Sir W, 

 Denison, "Varieties of Vice-Kegal liife," vol. i, 1870, p. 410. For 

 tlie Todas, see Col. Marshall's work, 1873, p. 110. For the Western 

 Islands of Scotland. Dr. Mitchell, "Edinburgh Medical Journal," 

 March to June, 1865. 



