the hard tip to the beak of unhatched birds,
used for breaking the eggs. It has been asserted, that of the best
short-beaked tumbler-pigeons a greater number perish in the egg than are
able to get out of it; so that fanciers assist in the act of hatching.
Now, if nature had to make the beak of a full-grown pigeon very short
for the bird's own advantage, the process of modification would be very
slow, and there would be simultaneously the most rigorous selection
of all the young birds within the egg, which had the most powerful and
hardest beaks, for all with weak beaks would inevitably perish: or, more
delicate and more easily broken shells might be selected, the thickness
of the shell being known to vary like every other structure.

It may be well here to remark that 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 that there is any variability in a favourable direction,
will tend to propagate their kind in larger numbers than the less
well adapted. If the numbers be wholly kept down by the causes just
indicated, as will often have been the case, natural selection will
be powerless in certain beneficial directions; but this is no valid
objection to its efficiency at other times and in other ways; for we
are far from having any reason to suppose that many species ever undergo
modification and improvement at the same time in the same area