Such study as I have been able to give to nature makes me believe that
parts or organs which are highly developed, were acquired at some
period for a special purpose. With those antelopes in which the adult
male is more strongly-coloured than the female, and with those monkeys
in which the hair on the face is elegantly arranged and coloured in a
diversified manner, it seems probable that the crests and tufts of hair
were gained as ornaments; and this I know is the opinion of some
naturalists. If this be correct, there can be little doubt that they
were gained or at least modified through sexual selection; but how far
the same view may be extended to other mammals is doubtful.
COLOUR OF THE HAIR AND OF THE NAKED SKIN.
I will first give briefly all the cases known to me of male quadrupeds
differing in colour from the females. With Marsupials, as I am informed
by Mr. Gould, the sexes rarely differ in this respect; but the great
red kangaroo offers a striking exception, delicate blue being the
prevailing tint in those parts of the female which in the male are
red. (19. Osphranter rufus, Gould, Mammals of Australia, 1863, vol.
ii. On the Didelphis, Desmarest, Mammalogie, p. 256.) In the
Didelphis opossum of Cayenne the female is said to be a little more red
than the male. Of the Rodents, Dr. Gray remarks: African squirrels,
especially those found in the tropical regions, have the fur much
brighter and more vivid at some seasons of the year than at others, and
the fur of the male is generally brighter than that of the female.
(20. Annals and Magazine of Natural History, Nov. 1867, p. 325. On
the Mus minutus, Desmarest, Mammalogie, p. 304.) Dr. Gray informs me
that he specified the African squirrels, because, from their unusually
bright colours, they best exhibit this difference. The female of the
Mus minutus of Russia is of a paler and dirtier tint than the male. In
a large number of bats the fur of the male is lighter than in the
female. (21. J.A. Allen, in Bulletin of Mus. Comp. Zoolog. of
Cambridge, United States, 1869, p. 207. Mr. Dobson on sexual
characters in the Chiroptera, Proceedings of the Zoological Society,
1873, p. 241. Dr. Gray on Sloths, ibid. 1871, p. 436.) Mr. Dobson also
remarks, with respect to these animals: Differences, depending partly
or entirely on the possession by the male of fur of a much more
brilliant hue, or distinguished by different markings or by the greater
length of certain portions, are met only, to any appreciable extent, in
the frugivorous bats in which the sense of sight is well developed.
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