acquire brilliant colours and would transmit them exclusively to their
male offspring. But I by no means wish to maintain that the influence
of age on the form of transmission, is the sole cause of the great
difference in brilliancy between the sexes of many birds.
When the sexes of birds differ in colour, it is interesting to
determine whether the males alone have been modified by sexual
selection, the females having been left unchanged, or only partially
and indirectly thus changed; or whether the females have been specially
modified through natural selection for the sake of protection. I will
therefore discuss this question at some length, even more fully than
its intrinsic importance deserves; for various curious collateral
points may thus be conveniently considered.
Before we enter on the subject of colour, more especially in reference
to Mr. Wallace s conclusions, it may be useful to discuss some other
sexual differences under a similar point of view. A breed of fowls
formerly existed in Germany (6. Bechstein, Naturgeschichte
Deutschlands, 1793, B. iii. 339.) in which the hens were furnished
with spurs; they were good layers, but they so greatly disturbed their
nests with their spurs that they could not be allowed to sit on their
own eggs. Hence at one time it appeared to me probable that with the
females of the wild Gallinaceae the development of spurs had been
checked through natural selection, from the injury thus caused to their
nests. This seemed all the more probable, as wing-spurs, which would
not be injurious during incubation, are often as well-developed in the
female as in the male; though in not a few cases they are rather larger
in the male. When the male is furnished with leg-spurs the female
almost always exhibits rudiments of them, the rudiment sometimes
consisting of a mere scale, as in Gallus. Hence it might be argued that
the females had aboriginally been furnished with well-developed spurs,
but that these had subsequently been lost through disuse or natural
selection. But if this view be admitted, it would have to be extended
to innumerable other cases; and it implies that the female progenitors
of the existing spur-bearing species were once encumbered with an
injurious appendage.
In some few genera and species, as in Galloperdix, Acomus, and the
Javan peacock (Pavo muticus), the females, as well as the males,
possess well-developed leg-spurs. Are we to infer from this fact that
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