I fear this letter will trouble you to read it. A very short answer
about your belief in regard to the [female symbol] finches and
Gallinaceae would suffice.--Believe me, my dear Wallace, yours very
sincerely,
CH. DARWIN.
* * * * *
_9 St. Mark's Crescent, S.W. September 27, 1868._
Dear Darwin,--Your view seems to be that variations occurring in one sex
are transmitted either to that sex exclusively or to both sexes equally,
or more rarely partially transferred. But we have every gradation of
sexual colours from total dissimilarity to perfect identity. If this is
explained solely by the laws of inheritance, then the colours of one or
other sex will be always (in relation to their environment) a _matter of
chance_. I cannot think this. I think Selection more powerful than laws
of inheritance, of which it makes use, as shown by cases of two, three
or four forms of female butterflies, all of which have, I have little
doubt, been specialised for protection.
To answer your first question is most difficult, if not impossible,
because we have no sufficient evidence in _individual cases of slight
sexual difference_, to determine whether the male alone has acquired his
superior brightness by sexual selection, or the female been made duller
by need of protection, or whether the two causes have acted.
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