the race-factor is, even if I have to trespass a little way into general
biology in order to do so.[2] And I shall not attempt to conceal the
difficulties relating to the race-problem. I know that the ordinary
reader is supposed to prefer that all the thinking should be done
beforehand, and merely the results submitted to him. But I cannot
believe that he would find it edifying to look at half-a-dozen books
upon the races of mankind, and find half-a-dozen accounts of their
relationships, having scarcely a single statement in common. Far
better face the fact that race still baffles us almost completely.
Yet, breed is there; and, in its own time and in its own way, breed
will out.

[Footnote 2: The reader is advised to consult also the more
comprehensive study on _Evolution_ by Professors Geddes and Thomson
in this series.]

Race or breed was a moment ago described as a factor in human nature.
But to break up human nature into factors is something that we can
do, or try to do, in thought only. In practice we can never succeed
in doing anything of the kind. A machine such as a watch we can take
to bits and then put together again. Even a chemical compound such
as water we can resolve into oxygen and hydrogen and then reproduce
out of its elements. But to dissect a living thing is to kill it once
and for all. Life, as was said in the first chapter, is something unique,
with the unique property of being able to evolve. As life evolves,
that is to say changes, by being handed on from certain forms to certain
other forms, a partial rigidity marks the process together with a
partial plasticity. There is a stiffening, so to speak, that keeps
the life-force up to a point true to its old direction; though, short
of that limit, it is free to take a new line of its own. Race, then,