it again, at length you will find that out of all your varieties only
two or three have lived, or perhaps even only one. There were one or
two varieties which were best fitted to get on, and they have killed
out the other kinds in just the same way and with just the same
certainty as if you had taken the trouble to remove them. As I have
already said, the operation of nature is exactly the same as the
artificial operation of man.

But if this be true of that simple case, which I put before you, where
there is nothing but the rivalry of one member of a species with
others, what must be the operation of selective conditions, when you
recollect as a matter of fact, that for every species of animal or
plant there are fifty or a hundred species which might all, more or
less, be comprehended in the same climate, food, and station;--that
every plant has multitudinous animals which prey upon it, and which are
its direct opponents; and that these have other animals preying upon
them,--that every plant has its indirect helpers in the birds that
scatter abroad its seed, and the animals that manure it with their
dung;--I say, when these things are considered, it seems impossible
that any variation which may arise in a species in nature should not
tend in some way or other either to be a little better or worse than
the previous stock; if it is a little better it will have an advantage
over and tend to extirpate the latter in this crush and struggle; and if
it is a little worse it will itself be extirpated.

I know nothing that more appropriately expresses this, than the phrase,
"the struggle for existence"; because it brings before your minds, in a
vivid sort of way, some of the simplest possible circumstances
connected with it. When a struggle is intense there must be some who
are sure to be trodden down, crushed, and overpowered by others; and