73. He here treats in fuller
detail the view already published in the _Westminster Review_ for July,
1867, p. 38. The rule which Wallace believes, with very few exceptions,
to hold good is, "that when both sexes are of strikingly gay and
conspicuous colours, the nest is ... such as to conceal the sitting
bird; while, whenever there is a striking contrast of colours, the male
being gay and conspicuous, 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.
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