NATURAL SELECTION IN MAN 199 



infants are very young that the death rate is by far the highest. 

 An indiscriminate death rate not only tends to mask the operation 

 of natural selection, but it interferes with its action. The more 

 the purely fortuitous causes of death are removed the more truly 

 selective the remaining part of the death rate becomes. It is 

 probable that many important causes of infant mortality could be 

 removed without interfering greatly with the kind of selective 

 elimination which is of value in maintaining racial vitality. 

 Certain congenital variations may lessen the chances of survival 

 as an infant, but once the period of infancy is passed there may 

 be no deleterious effect in the later years of life. Immaturity 

 at birth may lessen an infant's chance of life, but after a few 

 weeks have passed there may be no more trouble from this cir- 

 cumstance. The lessening of infant mortality which is now being 

 so successfully accomplished may not be so disadvantageous 

 racially after all. It possibly may be of greater racial advantage 

 to shield infancy as much as possible and thus allow an increase 

 of deaths to occur later in life when the death rate is apt to be 

 more discriminating. It is only those infant traits which are 

 correlated with undesirable adult characteristics which it would 

 be of advantage to have eliminated from the race, and it is not 

 clear what is the best method of securing this result. 



There is reason to believe that a considerable part of the 

 infant death rate is due not to any inherent weakness in the 

 infants themselves, but to defects in the stock which are mani- 

 fested in later years. Just as there may be variations which are 

 injurious to infancy but have no effect on the welfare of an older 

 person, so there are variations which will tend to be eliminated in 

 older persons but which have little immediate effect upon infancy. 

 In the latter class are to be included those inherent defects of 

 mind and character which are most conspicuously revealed after 

 several years of life. While the lower types of mental defectives 

 may be more apt to succumb at all ages, the high-grade morons 

 and people of dull mentality are frequently of good physical 

 constitution, and it is probable that their infants under good 

 care would have as low a death rate as those born of more intelli- 



