nclusion ought, I
think, to depend upon what we mean by an explanation in the case which
is before us. If we mean only that, given the large class of known facts
and unknown causes which are conveniently summarized under the terms
Heredity and Variability, then the further facts of Struggle and
Survival serve, in some considerable degree or another, to account for
the phenomena of adaptive evolution, I cannot see any room to question
that the evidence is sufficient to prove the statement. But it is clear
that by taking for granted these great facts of Heredity and
Variability, we have assumed the larger part of the problem as a whole.
Or, more correctly, by thus generalizing, in a merely verbal form, all
the unknown causes which are concerned in these two great factors of the
process in question, we are not so much as attempting to explain the
precedent causation which serves as a condition to the process. Much
more than half the battle would already have been won, had Darwin's
predecessors been able to explain the causes of Heredity and Variation;
hence it is but a very partial victory which we have hitherto gained in
our recent discovery of the effects of Struggle and Survival.

Yet partial though it be in relation to the whole battle, in itself, or
considered absolutely, there can be no reasonable doubt that it
constitutes the greatest single victory which has ever been gained by
the science of Biology. For this very reason, however, it behoves us to
consider all the more carefully the extent to which it goes. But my
discussion of this matter must be relegated to the next volume, where I
hope to give abundant proof of the soundness of Darwin's judgment as
conveyed in the words:--"I am convinced that natural selection has been
the main, but not the exclusive, means of modification."

CHAPTER X.

THE THEORY OF SEXUAL SELECTION, AND CONCLUDING REMARKS.

Although the explanatory value of the Darwinian theory of natural
selection is, as we have now seen, incalculably great, it nevertheless
does not meet those phenomena of organic nature which perhaps more than
any other attract the general attention, as well as the general
admiration, of mankind: I mean all that class of phenomena which go to
constitute the Beautiful. Whatever value beauty as such may have, it
clearly has not a life-preserving value. The gorgeous plumage of a
peacock, for instance, is of no advantage to the peacock in his struggle
for life, an