appear oftener in the
male than in the female. Secondly, characters may be developed and be
confined to the male, and long afterwards be transferred to the female.
Thirdly, characters may arise in either sex and be transmitted to both
sexes, either in an equal or unequal degree. In this latter case I have
supposed that the survival of the fittest has come into play with female
birds and kept the female dull-coloured. With respect to the absence of
spurs in the female gallinaceous birds, I presume that they would be
in the way during incubation; at least I have got the case of a German
breed of fowls in which the hens were spurred, and were found to disturb
and break their eggs much. With respect to the females of deer not
having horns, I presume it is to save the loss of organised matter. In
your note you speak of sexual selection and protection as sufficient to
account for the colouring of all animals, but it seems to me doubtful
how far this will come into play with some of the lower animals, such as
sea anemones, some corals, etc., etc. On the other hand Hackel (430/1.
See "Descent of Man" (1901) page 402.) has recently well shown that
the transparency and absence of colour in the lower oceanic animals,
belonging to the most different classes, may be well accounted for on
the principle of protection.

Some time or other I should like much to know where your paper on the
nests of birds has appeared, and I shall be extremely anxious to read
your paper in the "Westminster Review." (430/2. "Westminster Review,"
July, 1867.) Your paper on the sexual colouring of birds will, I have
no doubt, be very striking. Forgive me, if you can, for a touch of
illiberality about your paper.

LETTER 431. TO A.R. WALLACE. March 19th, 1868.

(431/1. "The Variation of Animals and Plants" having been published on
January 30th, 1868, Mr. Darwin notes in his diary that on February 4th
he "Began on Man and Sexual Selection." He had already (in 1864 and
1867) corresponded with Mr. Wallace on these questions--see for
instance the "Life and Letters," III., page 89; but, owing to various
interruptions, serious work on the subject did not begin until 1869. The
following quotations show the line of work undertaken early in 1868.

Mr. Wallace wrote (March 19th, 1868): "I am glad you have got good
materials on sexual selection. It is no doubt a difficult subject.
One difficulty to me is, that I do not see how the constant MINUTE
variations, whi