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Descent of Man [ 1871]

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Author Topic: Descent of Man [ 1871]  (Read 2925 times)
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« Reply #120 on: February 09, 2009, 03:10:24 pm »

* Westminster Review, July, 1867, p. 7.
  *(2) "Indian Cyprinidae," by Mr. M'Clelland, Asiatic Researches,
vol. xix., part ii., 1839, p. 230.

  We have now to consider whether, when the male differs in a marked
manner from the female in colour or in other ornaments, he alone has
been modified, the variations being inherited by his male offspring
alone; or whether the female has been specially modified and
rendered inconspicuous for the sake of protection, such
modifications being inherited only by the females. It is impossible to
doubt that colour has been gained by many fishes as a protection: no
one can examine the speckled upper surface of a flounder, and overlook
its resemblance to the sandy bed of the sea on which it lives. Certain
fishes, moreover, can through the action of the nervous system
change their colours in adaptation to surrounding objects, and that
within a short time.* One of the most striking instances ever recorded
of an animal being protected by its colour (as far as it can be judged
of in preserved specimens), as well as by its form, is that given by
Dr. Gunther*(2) of a pipe-fish, which, with its reddish streaming
filaments, is hardly distinguishable from the sea-weed to which it
clings with its prehensile tail. But the question now under
consideration is whether the females alone have been modified for this
object. We can see that one sex will not be modified through natural
selection for the sake of protection more than the other, supposing
both to vary, unless one sex is exposed for a longer period to danger,
or has less power of escaping from such danger than the other; and
it does not appear that with fishes the sexes differ in these
respects. As far as there is any difference, the males, from being
generally smaller and from wandering more about, are exposed to
greater danger than the females; and yet, when the sexes differ, the
males are almost always the more conspicuously coloured. The ova are
fertilised immediately after being deposited; and when this process
lasts for several days, as in the case of the salmon,*(3) the
female, during the whole time, is attended by the male. After the
ova are fertilised they are, in most cases, left unprotected by both
parents, so that the males and females, as far as oviposition is
concerned, are equally exposed to danger, and both are equally
important for the production of fertile ova; consequently the more
or less brightly-coloured individuals of either sex would be equally
liable to be destroyed or preserved, and both would have an equal
influence on the colours of their offspring.

  * G. Pouchet, L'Institut., Nov. 1, 1871, p. 134.
  *(2) Proc. Zoolog. Soc., 1865, p. 327, pls. xiv. and xv.
  *(3) Yarrell, British Fishes, vol. ii., p. 11.

  Certain fishes belonging to several families, make nests, and some
of them take care of their young when hatched. Both sexes of the
bright-coloured Crenilabrus massa and melops work together in building
their nests with seaweed, shells, &c.* But the males of certain fishes
do all the work, and afterward take exclusive charge of the young.
This is the case with the dull-coloured gobies,*(2) in which the sexes
are not known to differ in colour, and likewise with the
sticklebacks (Gasterosteus), in which the males become brilliantly
coloured during the spawning season. The male of the smooth-tailed
stickleback (G. leiurus) performs the duties of a nurse with exemplary
care and vigilance during a long time, and is continually employed
in gently leading back the young to the nest, when they stray too far.
He courageously drives away all enemies including the females of his
own species. It would indeed be no small relief to the male, if the
female, after depositing her eggs, were immediately devoured by some
enemy, for he is forced incessantly to drive her from the nest.*(3)

  * According to the observations of M. Gerbe; see Gunther's Record of
Zoolog. Literature, 1865, p. 194.
  *(2) Cuvier, Regne Animal, vol. ii., 1829, p. 242.
  *(3) See Mr. Warington's most interesting description of the
habits of the Gasterosteus leiurus in Annals and Magazine of Nat.
History, November, 1855.

  The males of certain other fishes inhabiting South America and
Ceylon, belonging to two distinct Orders, have the extraordinary habit
of hatching within their mouths, or branchial cavities, the eggs
laid by the females.* I am informed by Professor Agassiz that the
males of the Amazonian species which follow this habit, "not only
are generally brighter than the females, but the difference is greater
at the spawning-season than at any other time." The species of
Geophagus act in the same manner; and in this genus, a conspicuous
protuberance becomes developed on the forehead of the males during the
breeding-season. With the various species of chromids, as Professor
Agassiz likewise informs me, sexual differences in colour may be
observed, "whether they lay their eggs in the water among aquatic
plants, or deposit them in holes, leaving them to come out without
further care, or build shallow nests in the river mud, over which they
sit, as our Pomotis does. It ought also to be observed that these
sitters are among the brightest species in their respective
families; for instance, Hygrogonus is bright green, with large black
ocelli, encircled with the most brilliant red." Whether with all the
species of chromids it is the male alone which sits on the eggs is not
known. It is, however, manifest that the fact of the eggs being
protected or unprotected by the parents, has had little or no
influence on the differences in colour between the sexes. It is
further manifest, in all the cases in which the males take exclusive
charge of the nests and young, that the destruction of the
brighter-coloured males would be far more influential on the character
of the race, than the destruction of the brighter-coloured females;
for the death of the male during the period of incubation or nursing
would entail the death of the young, so that they could not inherit
his peculiarities; yet, in many of these very cases the males are more
conspicuously coloured than the females.

  * Prof. Wyman, in Proc. Boston Soc. of Nat. Hist., Sept. 15, 1857.
Also Prof. Turner, in Journal of Anatomy and Physiology, Nov. 1, 1866,
p. 78. Dr. Gunther has likewise described other cases.

  In most of the Lophobranchii (pipe-fish, Hippocampi, &c.) the
males have either marsupial sacks or hemispherical depressions on
the abdomen, in which the ova laid by the female are hatched. The
males also shew great attachment to their young.* The sexes do not
commonly differ much in colour; but Dr. Gunther believes that the male
Hippocampi are rather brighter than the females. The genus
Solenostoma, however, offers a curious exceptional case,*(2) for the
female is much more vividly-coloured and spotted than the male, and
she alone has a marsupial sack and hatches the eggs; so that the
female of Solenostoma differs from all the other Lophobranchii in this
latter respect, and from almost all other fishes, in being more
brightly-coloured than the male. It is improbable that this remarkable
double inversion of character in the female should be an accidental
coincidence. As the males of several fishes, which take exclusive
charge of the eggs and young, are more brightly coloured than the
females, and as here the female Solenostoma takes the same charge
and is brighter than the male, it might be argued that the conspicuous
colours of that sex which is the more important of the two for the
welfare of the offspring, must be in some manner protective. But
from the large number of fishes, of which the males are either
permanently or periodically brighter than the females, but whose
life is not at all more important for the welfare of the species
than that of the female, this view can hardly be maintained. When we
treat of birds we shall meet with analogous cases, where there has
been a complete inversion of the usual attributes of the two sexes,
and we shall then give what appears to be the probable explanation,
namely, that the males have selected the more attractive females,
instead of the latter having selected, in accordance with the usual
rule throughout the animal kingdom, the more attractive males.

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