It is immensely difficult to separate the effects of the various factors.

Yet surely the race-factor counts for something in the mental constitution.

Any breeder of horses will tell you that neither the climate of Newmarket, nor careful training, nor any quantity of oats, nor anything else, will put racing mettle into cart-horse stock.
In what follows, then, I shall try to show just what the problem about 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.