250 THE DESCENT OF MAN 



in summer, and also the various hill-tribes of India, suffer 

 from dysentery and fever when on the plains; and they die 

 if they attempt to pass the whole year there. 



We thus see that many of the wilder races of man are apt 

 to suffer much m health when subjected to changed condi- 

 tions or habits of life, and not exclusively from being trans- 

 ported to a new climate. Mere alterations in habits, which 

 do not appear injurious in themselves, seem to have this 

 same effect; and in several cases the children are particu- 

 larly liable to suffer. It has often been said, as Mr. Mac- 

 namara remarks, that man can resist with impunity the 

 greatest diversities of climate and other changes; but this 

 is true only of the civilized races. Man in his wild condi- 

 tion seems to be in this respect almost as susceptible! as his 

 nearest allies, the anthropoid apes, which have never yet 

 survived long, when removed from their native country. 



Lessened fertility from changed conditions, as in the 

 case of the Tasmanians, Maories, Sandwich Islanders, and 

 apparently the Australians, is still more interesting than 

 their liability to ill-health and death; for even a slight de- 

 gree of infertility, combined with those other causes which 

 tend to check the increase of every population, would sooner 

 or later lead to extinction. The diminution of fertility may 

 be explained in some cases by the profligacy of the women 

 •(as until lately with the Tahitians), but Mr. Fenton has 

 shown that this explanation by no means suffices with the 

 New Zealanders, nor does it with the Tasmanians. 



In the paper above quoted, Mr. Macnamara gives reasons 

 for believing that the inhabitants of districts subject to 

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

 of the above cases. Some writers have suggested that the 

 aborigines of islands have suffered in fertility and health 

 from long-continued interbreeding; but in the above cases 

 infertility has coincided too closely with the arrival of Euro- 

 peans 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 interbreeding, especially in areas so 



