the female till it becomes positively injurious
to her during incubation and the race is in danger of extinction, do you
not think that all the females who had acquired less of the male's
bright colours or who themselves varied in a protective direction would
be preserved, and that thus a good protective colouring would be
acquired? If you admit that this could occur, and can show no good
reason why it should not often occur, then we no longer differ, for this
is the main point of my view.

Have you ever thought of the red wax-tips of the Bombycilla beautifully
imitating the red fructification of lichens used in the nest, and
therefore the females have it too? Yet this is a very sexual-looking
character.

We begin printing this week.--Yours very faithfully,

ALFRED R. WALLACE.

P.S.--Pray don't distress yourself on this subject. It will all come
right in the end, and after all it is only an episode in your great
work.--A.R.W.

* * * * *

_9 St. Mark's Crescent, N.W. October 4, 1868._

Dear Darwin,--I should have answered your letter before, but have been
very busy reading over my MSS. the last time before going to press,
drawing maps, etc. etc.

Your first question cannot be answered, because we have not, in
_individual cases_ of _slight sexual_ difference, sufficient evidence to
determine how much of that difference is due to sexual selection acting
on the male, how much to natural selection (protective) acting on the
female, or how much of the difference may be due to inherited
differences from ancestors who lived under different conditions. On your
second question I can give an opinion. I do think the females of the
Gallinaceae you mention have been either _modified_; or _prevented from
acquiring much of the brighter plumage of the males_, by the need of
protection. I know that _Gallus bankiva_ frequents drier and more open
situations than _Pavo muticus_, which in Java is found among grassy and
leafy vegetation corresponding with the colours of the two females. So
the Argus pheasants, male and female, are, I feel sure, protected by
their tints corresponding to dead leaves of the dry lofty forests in
which they dwell; and the female of the gorgeous fire-back pheasant,
_Lophura viellottii_, is of a very similar rich brown colour.

These and many other colours of female birds seem to me exactly
analogous to the colours of _both sexes_ in such groups as the snipes,
woodcocks, pl