With all beings there must be much fortuitous destruction, which can
have little or no influence on the course of natural selection. For
instance, a vast number of eggs or seeds are annually devoured, and
these could be modified through natural selection only if they varied
in some manner which protected them from their enemies. Yet many of
these eggs or seeds would perhaps, if not destroyed, have yielded
individuals better adapted to their conditions of life than any of those
which happened to survive. So, again, a vast number of mature animals
and plants, whether or not they be the best adapted to their conditions,
must be annually destroyed by accidental causes, which would not be in
the least degree mitigated by certain changes of structure or
constitution which would in other ways be beneficial to the species.

But let the destruction of the adults be ever so heavy, if the number
which can exist in any district be not wholly kept down by such
causes--or, again, let the destruction of eggs or seeds be so great that
only a hundredth or a thousandth part are developed--yet of those which
do survive, the best adapted individuals, supposing there is any
variability in a favourable direction, will tend to propagate their kind
in larger numbers than the less well adapted.

On our theory the continued existence of lowly organisms offers no
difficulty; for natural selection does not necessarily include
progressive development; it only takes advantage of such variations as
arise and are beneficial to each creature under its complex relations of
life.

The mere lapse of time by itself does nothing, either for or against
natural selection. I state this because it has been erroneously asserted
that the element of time has been assumed by me to play an all-important
part in modifying species, as if all the forms of life were necessarily
undergoing change through some innate law.

_V.--Sexual Selection_

This form of selection depends, not on a struggle for existence in
relation to other organic beings or to external conditions, but on a
struggle between the individuals of one sex, generally the males, for
the possession of the other sex. The result is not death to the
unsuccessful competitor, but few or no offspring. Sexual selection is,
therefore, less rigorous than natural selection. Generally, the most
vigorous males, those which are best fitted for their places in Nature,
will leave most progeny. But, in many cases,