Origin of Species Variorum

→ more 1859 1860 1861 1866

a greater number 1869 1872

↑ 6 blocks not present in 1859 1860 1861 1866 1869; present in 1872

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.

→ the same fact probably occurs 1859 1860 1861 1866

the same fact no doubt occurs 1869

so no doubt it will be 1872

→ and if so, 1859 1860 1861 1866 1869

Thus it is rendered possible for the two sexes to be modified through 1872

→ will be able to modify one sex in its functional 1859 1860 1861 1866 1869

in 1872

→ the other sex, or in relation to wholly 1859 1860 1861 1866 1869

OMIT 1872

→ in the two sexes, 1859 1860 1861 1866 1869

OMIT 1872

→ with insects. 1859 1860 1861 1866 1869

or for one sex to be modified in relation to the other sex, as commonly occurs. 1872

to modify the structure of one species, without giving it any advantage, for the good of another species; and though statements to this effect may be found in works of natural history, I cannot find one case which will bear investigation. A structure used only once in an

animals

animal's

~~whole~~

whole

life, if of high importance to it, might be modified to any extent by natural selection; for instance, the great jaws possessed by certain insects,

and

....

used exclusively for opening the cocoon— or the hard tip to the beak of

unhatched

nestling

birds, used for breaking the egg. It has been asserted, that of the best short-beaked tumbler-pigeons →more perish in the egg than are able to get out of it; so that fanciers assist in the act of hatching.

Now

Now,

if nature had to make the beak of a full-grown pigeon very short for the

birds

bird's

own advantage, the process of modification would be very slow, and there would be simultaneously the most rigorous selection of

all the

the

young birds within the egg, which had the most powerful and hardest beaks, for all with weak beaks would inevitably

perish:

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. ↑

Sexual

Selection .—

Selection. —

Selection.

Inasmuch as peculiarities often appear under domestication in one sex and become hereditarily attached to that sex, →the same fact probably occurs under

nature.

nature,

→and if so, natural selection →will be able to modify one sex in its functional

relation

relations

to →the other sex, or in relation to wholly different habits of

life,

life

→in the two sexes, as is sometimes the

case;

case

→with insects.