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- 
