vill Preface 
when I should only have been justified in stating the different 
aspects of the question. But this will do little harm provided 
the issue has been sharply drawn. Indeed, it seems to me 
that the only scientific value, that a discussion of what the 
French call “les grands problémes de la Biologie” has, is to 
get a clearer understanding of the relation of what is known 
to what is unknown or only surmised. 
In some quarters speculation concerning the origin of the 
adaptation of living things is frowned upon, but I have failed 
to observe that the critics themselves refrain entirely from 
theorizing. They shut one door only to open another, which 
also leads out into the dark. To deny the right to speculative 
thought would be to deny the right to use one of the best 
tools of research. 
Yet it must be admitted that all speculation is not equally 
valuable. The advance of science in the last hundred years 
has shown that the kind of speculation that has real worth is 
that which leads the way to further research and possible 
discovery. Speculation that leads to this end must be recog- 
nized as legitimate. It becomes useless when it deals with 
problems that cannot be put to the actual test of observation 
or experiment. It is in this spirit that I have approached the 
topics discussed in the following pages. 
The unsophisticated man believes that all other animals 
exist to minister to his welfare; and from this point of view 
their adaptations are thought of solely in their relation to 
himself. A step in advance was taken when the idea was 
conceived that adaptations are for the good of the organisms 
themselves. It seemed a further advance when the con- 
clusion was reached that the origin of adaptations could be 
accounted for, as the result of the benefit that they conferred 
on their possessor. This view was the outcome of the accep- 
tation of the theory of evolution, combined with Darwin’s 
theory of natural selection. It is the view held by most 
biologists at the present time; but I venture to prophesy 
