thousand years, it may last for twenty or thirty thousand years more,
without obvious change; but, as surely as it has followed upon a very
different state, so it will be followed by an equally different
condition. That which endures is not one or another association of
living forms, but the process of which the cosmos is the product, and
of which these are among the transitory expressions. And in the living
world, one of the most characteristic features of this cosmic process
is the struggle for existence, the competition of each with all, the
result of which is the selection, that is to say, the survival of
those forms which, on the whole, are best adapted, to the conditions
which at any period obtain; and which are, therefore, in that respect,
and only in that respect, the fittest.* The acme reached by the cosmic
[5] process in the vegetation of the downs is seen in the turf, with
its weeds and gorse. Under the conditions, they have come out of the
struggle victorious; and, by surviving, have proved that they are the
fittest to survive.

* That every theory of evolution must be consistent not merely
with progressive development, but with indefinite persistence
in the same condition and with retrogressive modification, is a
point which I have insisted upon repeatedly from the year 1862
till now. See Collected Essays, vol. ii. pp. 461-89; vol. iii.
p. 33; vol. viii. p. 304. In the address on "Geological
Contemporaneity and Persistent Types" (1862), the
paleontological proofs of this proposition were, I believe,
first set forth.

That the state of nature, at any time, is a temporary phase of a
process of incessant change, which has been going on for innumerable
ages, appears to me to be a proposition as well established as any in