(or any
other insect?) _alone_ mimicking a Danais, etc.

11. But colour is more frequent in males, and _variations_ always seem
ready for purposes of sexual or other selection.

12. The fair inference seems to be that given in proposition 5 of the
general argument, viz. that _each species_ and _each sex_ can only be
modified by selection just as far as is absolutely necessary, not a step
farther. A male, being by structure and habits less exposed to danger
and less requiring protection than the female, cannot have more
protection given to it by Natural Selection, but a female must have some
extra protection to balance the greater danger, and she rapidly acquires
it in one way or another.

13. An objection derived from cases like male fish, which seem to
require protection, yet having brighter colours, seems to me of no more
weight than is that of the existence of many white and unprotected
species of Leptalis to Bates's theory of mimicry, that only one or two
species of butterflies perfectly resemble leaves, or that the instincts
or habits or colours that seem essential to the preservation of one
animal are often totally absent in an allied species.

* * * * *

_Down, Bromley, Kent. September 23, 1868._

My dear Wallace,--I am very much obliged for all your trouble in writing
me your long letter, which I will keep by me and ponder over. To answer
it would require at least 200 folio pages! If you could see how often I
have rewritten some pages, you would know how anxious I am to arrive as
near as I can to the truth. We differ, I think, chiefly from fixing our
minds perhaps too closely on different points, on which we agree: I lay
great stress on what I know takes place under domestication: I think we
start with different fundamental notions on inheritance. I find it most
difficult, but not, I think, impossible, to see how, for instance, a few
red feathers appearing on the head of a male bird, and which _are at
first transmitted to both sexes_, could come to be transmitted to males
alone;[72] but I have no difficulty in making the whole head red if the
few red feathers in the male from the first tended to be sexually
transmitted. I am quite willing to admit that the female may have been
modified, either at the same time or subsequently, for protection, by
the accumulation of variations limited in their transmission to the
female sex. I owe to your writings the consideration of this lat