stands for the stiffening in the evolutionary process. Just up to what
point it goes in any given case we probably can never quite tell. Yet,
if we could think our way anywhere near to that point in regard to
man, I doubt not that we should eventually succeed in forging a fresh
instrument for controlling the destinies of our species, an instrument
perhaps more powerful than education itself--I mean, eugenics, the
art of improving the human breed.

To see what race means when considered apart, let us first of all take
your individual self, and ask how you would proceed to separate your
inherited nature from the nature which you have acquired in the course
of living your life. It is not easy. Suppose, however, that you had
a twin brother born, if indeed that were possible, as like you as one
pea is like another. An accident in childhood, however, has caused
him to lose a leg. So he becomes a clerk, living a sedentary life in
an office. You, on the other hand, with your two lusty legs to help
you, become a postman, always on the run. Well, the two of you are
now very different men in looks and habits. He is pale and you are
brown. You play football and he sits at home reading. Nevertheless,
any friend who knows you both intimately will discover fifty little
things that bespeak in you the same underlying nature and bent. You
are both, for instance, slightly colour-blind, and both inclined to
fly into violent passions on occasion. That is your common inheritance
peeping out--if, at least, your friend has really managed to make
allowance for your common bringing-up, which might mainly account for
the passionateness, though hardly for the colour-blindness.

But now comes the great difficulty. Let us further suppose that you
two twins marry wives who are also twins born as like as two peas;
and each pair of you has a family. Which of the two batches of children