oubt that healthy and vigorous birds best provide for their
young, natural selection, by always placing its premium on health and
vigour in the males, thus also incidentally promotes, through correlated
growth, their superior coloration.

Again, with regard to the display which is practised by male birds, and
which constitutes the strongest of all Mr. Darwin's arguments in favour
of sexual selection, Mr. Wallace points out that there is no evidence of
the females being in any way affected thereby. On the other hand, he
argues that this display may be due merely to general excitement; and he
lays stress upon the more special fact that moveable feathers are
habitually erected under the influence of anger and rivalry, in order to
make the bird look more formidable in the eyes of antagonists.

Furthermore, he adduces the consideration that, even if the females are
in any way affected by colour and its display on the part of the males,
and if, therefore, sexual selection be conceded a true principle in
theory, still we must remember that, as a matter of fact, it can only
operate in so far as it is allowed to operate by natural selection. Now,
according to Mr. Wallace, natural selection must wholly neutralize any
such supposed influence of sexual selection. For, unless the survivors
in the general struggle for existence happen to be those which are also
the most highly ornamented, natural selection must neutralize and
destroy any influence that may be exerted by female selection. But
obviously the chances against the otherwise best fitted males happening
to be likewise the most highly ornamented must be many to one, unless,
as Wallace supposes, there is some correlation between embellishment and
general perfection, in which case, as he points out, the theory of
sexual selection lapses altogether, and becomes but a special case of
natural selection.

Once more, Mr. Wallace argues that the evidence collected by Mr. Darwin
himself proves that each bird finds a mate under any circumstances--a
general fact which in itself must quite neutralize any effect of sexual
selection of colour or ornament, since the less highly coloured birds
would be at no disadvantage as regards the leaving of healthy progeny.

Lastly, he urges the high improbability that through thousands of
generations all the females of any particular species--possibly spread
over an enormous area--should uniformly and always have displayed
exactly the same taste wi