1 68 THE EVOLUTION OF MAN 



sanitation have made great advances in recent years and this 

 has had a beneficial influence on the health and vigor of this 

 generation, but there is no satisfactory evidence that these 

 effects are inherited. The average length of life has been 

 increased, chiefly by saving the babies, but the maximum length 

 of life has not been raised; men live no longer now than in 

 the time of Methuselah, and since longevity is hereditary, it 

 may well be that the artificial prolongation of the lives of those 

 who are hereditarily weak and short-lived may actually reduce 

 the natural longevity of the race as a whole. 



Mental and moral degeneracy runs in families, as is proved 

 by such cases as the "Jukes," "Kalikaks," "Zeros," "Nams," 

 "Ishmaels," etc., but social selection against such groups is 

 pretty severe and it does not seem probable that extreme de- 

 fectives of this class are increasing very rapidly. Inmates of 

 custodial institutions are usually prevented from having off- 

 spring and they do not greatly threaten racial standards; the 

 greatest danger comes from somewhat less defective indi- 

 viduals who are at large and are free to have as many children 

 as they can. 



Retrogressive Selection of Civilization. Much worse than 

 this partial failure of natural selection is the retrogressive 

 selection of civilization. If society had deliberately set about 

 the propagation of the unfit it could hardly have devised 

 more effective means than many of those which are now in 

 vogue. Frequent wars have taken the best blood of the na- 

 tions, and while casualties in modern battle are more or less 

 indiscriminate, soldiers represent a selected group; those who 

 go to war are usually the young, the strong, the capable, while 

 the weak, incompetent, and degenerate are left behind as unfit 

 for military service. Furthermore, these casualties must be 

 doubled when their influence on the race is considered, for in 

 general every man killed leaves one woman unmated for life. 

 As a result of the last war millions of women can never marrv 



