uous, the female dull and obscure, the nest is open
and the sitting bird exposed to view." At this time Wallace allowed
considerably more influence to _sexual_ selection (in combination with
the need of protection) than in his later writings. See his letter to
Darwin of July 23, 1877 (p. 298), which fixes the period at which the
change in his views occurred. He finally rejected Darwin's theory that
colours "have been developed by the preference of the females, the more
ornamented males becoming the parents of each successive generation."
(_See_ "Darwinism," 1889, p. 285.)

_Down, Bromley, Kent, S.E. April 15, 1868._

My dear Wallace,--I have been deeply interested by your admirable
article on Birds' Nests. I am delighted to see that we really differ
very little--not more than two men almost always will. You do not lay
much or any stress on new characters spontaneously appearing in one sex
(generally the male) and being transmitted exclusively, or more commonly
only in excess, to that sex. I, on the other hand, formerly paid far too
little attention to protection. I had only a glimpse of the truth. But
even now I do not go quite as far as you. I cannot avoid thinking rather
more than you do about the exceptions in nesting to the rule, especially
the partial exceptions, i.e. when there is some little difference
between the sexes in species which build concealed nests. I am now quite
satisfied about the incubating males; there is so little difference in
conspicuousness between the sexes. I wish with all my heart I could go
the whole length with you. You seem to think that such birds probably
select the most beautiful females: I must feel some doubt on this head,
for I can find no evidence of it. Though I am writing so carping a note,
I admire the article _thoroughly_.

And now I want to ask a question. When female butterflies are more
brilliant than their males, you believe that they have in most cases, or
in all cases, been rendered brilliant so as to mimic some other species
and thus escape danger. But can you account for the males not having
been rendered equally brilliant and equally protected? Although it may
be most for the welfare of the species that the female should be
protected, yet it would be some advantage, certainly no disadvantage,
for the unfortunate male to enjoy an equal immunity from danger. For my
part, I should say that the female alone had happened to vary in the
right manner, and that the benefic