have no desire to deny or even to question) can dispense with _guidance_
and the fixing of certain lines and limits within which, and of certain
types towards which, the development proceeds. That is our point.

It is hardly necessary to illustrate the enormous destruction of life
which goes on in the world. Even among the human race, the percentage of
infants that die in the first months of their life is very large. But in
the lower forms of life it is truly enormous. Only consider the myriads
of insects that perish from hunger or accident, and from the preying of
one species on another. If it were not so, the world would be overrun by
plagues of mice, of birds, of insects of all kinds, and indeed by
creatures of every grade. The term "struggle for existence" is, then,
not an inapt one. All forms of living creatures have to contend with
enemies which seek to prey upon or to destroy them, with the difficulty
of obtaining food, and with what I may call the chances of
nature--cold, storms, floods, disease, and so forth.

Now, it is obvious that if some creatures of a given kind possess some
accidental peculiarity or modification in their formation which gives
them (in one way or another) an advantage over their fellows, these
improved specimens are likely to survive, and, surviving, to have
offspring.

It is this perpetuation of advantageous changes, originally induced by
the circumstances of environment, that is indicated by the term "natural
selection." Nature chooses out the form best suited to the circumstances
which surround it, and this form lives while the others die out. And
this form goes on improving by slow successive changes, which make it
more and more fit for the continually changing circumstances of its
life.