iv PREFACE. 
The principles molding segregation, and so controlling variation 
and heredity, and the effects on racial and social evolution produced 
by such control, are presented with considerable fullness of illustra- 
tion on the biological side. For my purpose it did not seem necessary 
to dwell at equal length on the social aspects. 
Another broad department of the subject is referred to in only the 
briefest way. ‘This is the effect of amalgamation or regressive segrega- 
tion, both racial and social. I have, however, pointed out that in the 
history of man segregation was the leading factor through countless 
generations when races, languages, and institutions were becoming 
increasingly subdivided; and that it is only in modern times that the 
barriers to free intercourse have been so rapidly yielding that regres- 
sive segregation has been the predominant feature in human history. 
I have presented evidence that, even in the case of invertebrate 
animals, members of the same species, exposed to the same environ- 
ment in isolated groups, will often arrive at divergent methods of 
dealing with the environment, and so subject themselves to divergent 
forms of selection. If my contention is in accord with the facts, the 
assumption which we often meet that change in the organism is 
controlled in all its details by change in the environment, and that, 
therefore, human progress is ruled by an external fate, is certainly 
contrary to fact. 
It is of no little interest that the recent developments of biological 
science, in both Europe and America, are pointing, not only to the 
power of the organism to deal with the same environment in different 
ways, and so to determine the forms of what I have called active (or 
endonomic) selection, but also the power of many animals to deal with 
sudden changes in the environment in such a way that the group is 
saved from extinction till ‘‘cozncident variations’’ have time to arise, 
insuring completer adaptation to the new conditions through selection. 
The teachings of biology are thus coming more nearly into accord 
with that school of sociology which has for years maintained that the 
social group may learn to determine the form of its own social evolu- 
tion. We are thus led to hope that man will in time determine his 
own evolution, racial as well as social; for when sufficiently advanced 
to realize the breadth of the responsibilities resting upon him, the 
form of his racial inheritance will naturally be determined by the 
ideals shaping his social organization. 
In the third chapter, and again near the end of the last chapter, 
attention is called to the fact that, in accommodational and anticipa-. 
tory action, and in codéperation for the attainment of future results, 
all forms of life, from the earliest protozoa till we reach the highest 
