typical centre of their race, deteriorating in the first
case but not in the second. The two cases, though theoretically
distinct, are confused in reality, owing to the frequency with which
exceptional personal qualities connote the departure of the entire
nature of the individual from his ancestral type, and the formation
of a new strain having its own typical centre. It is hardly
necessary to add that it is in this indirect way that natural
selection improves a race. The two events of selection and
difference of race ought, however, to be carefully distinguished in
broad practical considerations, while the frequency of their
concurrence is borne in mind and allowed for.

So long as the race remains radically the same, the stringent
selection of the best specimens to rear and breed from, can never
lead to any permanent result. The attempt to raise the standard of
such a race is like the labour of Sisyphus in rolling his stone
uphill; let the effort be relaxed for a moment, and the stone will
roll back. Whenever a new typical centre appears, it is as though
there was a facet upon the lower surface of the stone, on which it
is capable of resting without rolling back. It affords a temporary
sticking-point in the forward progress of evolution. The causes that
check the unlimited improvement of highly-bred animals, so long as
the race remains unchanged, are many and absolute.

In the first place there is an increasing delicacy of constitution;
the growing fineness of limb and structure end, after a few
generations, in fragility. Overbred animals have little stamina;
they resemble in this respect the "weedy" colts so often reared from
first-class racers. One can perhaps see in a general way why this
should be so. Each individual is the outcome of a vast number of
organic elements of the most various species, just as some nation
might be the outcome of a vast number of castes of individuals, each
caste monopolising a special pursuit. Banish a number of the humbler
castes--the bakers, the bricklayers, and the smiths, and the nation
would soon come to grief. This is what is done in high breeding;
certain qualities are bred for, and the rest are diminished as far
as possible, but they cannot be dispensed with entirely.

The next difficulty lies in the diminished fertility of highly-bred
animals. It is not improbable that its cause is of the same
character as that of the delicacy of their constitution. Together
with infertil