204 APPENDIX II—INTENSIVE SEGREGATION. 
with the exception of a few of mankind, and still fewer of domestic 
animals, it may be truly said of every individual mammal that all its 
ancestry, through all generations since they became fairly mammalian, 
have had this instinct in full force; and yet it sometimes fails and the 
line of descent is cut short with the individual that fails. Till compara- 
tively recent times the same was true of man; but we now find some 
cases in which the young survive in spite of their inability to suck, 
and the constancy of this mammalian characteristic is being gradually 
impaired. There is also in some races an increasing tendency to 
shorter periods of lactation, or to the entire suppression of the func- 
tion; so that it seems not improbable that there may yet arise a 
variety of the human species in which the power will be comparatively 
obsolete. Under such conditions the instinct for sucking would cease 
to be of any advantage, while special advantage would accrue to those 
best able to thrive on the artificial food habitually provided by the 
parents. In some countries this would be the milk of ruminating 
animals, while in other countries it would be some vegetable prepara- 
tion. Through this diversity in the food provided by the parents for 
their infants and small children, there is even now a constant diversity 
in the parental selection prevailing in different countries. Diversity 
in the forms of parental selection is also produced by diversity in the 
clothing and artificial heat provided by parents; in the protection, on 
the one hand, of children from the wind and rain and direct rays of the 
sun, and on theother hand, their exposure to the same with shaven 
heads or naked bodies; and inthe methods of binding, cramping, and 
mutilating the head, feet, waist, and other parts of the body. From 
this point of view we see how largely the form of parental selection is 
determined by social custom, and how it is sometimes enforced by 
social selection, which excludes from the benefits of the caste or tribe 
all who have not passed through the ordeal. 
As filio-parental selection is due to different degrees of adaptation 
between the parent and offspring, it may be characterized not only by 
fatal departures in offspring from the characters required in their rela- 
tions to their parents, but by fatal departures in parents from the char- 
acters required in parents in their relations to their offspring. Asan 
example of the former, we may refer to the death at birth of children 
with excessively large heads; and as an example of the latter, to the 
death at birth of all the children of a mother with a contracted pelvis. 
(13) Dominational selection.—Variations that are equally fitted to 
cope with the environment may be divided into two classes—those 
better able and those less able to cope with other members of the 
species in the appropriation of resources. Increase of population and 
