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Descent of Man [ 1871]

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Bullseye
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« Reply #120 on: February 09, 2009, 03:10:05 pm »

* Yarrell, History of British Fishes, vol. ii., 1836, pp. 10, 12,
35.
  *(2) W. Thompson, in Annals and Magazine of Natural History, vol.
vi., 1841, p. 440.
  *(3) The American Agriculturalist, 1868, p. 100.
  *(4) Annals and Mag. of Nat. Hist., Oct., 1852.

  With respect to the courtship of fishes, other cases have been
observed since the first edition of this book appeared, besides that
already given of the stickleback. Mr. W. S. Kent says that the male of
the Labrus mixtus, which, as we have seen, differs in colour from
the female, makes "a deep hollow in the sand of the tank, and then
endeavours in the most persuasive manner to induce a female of the
same species to share it with him, swimming backwards and forwards
between her and the completed nest, and plainly exhibiting the
greatest anxiety for her to follow." The males of Cantharus lineatus
become, during the breeding-season, of deep leaden-black; they then
retire from the shoal, and excavate a hollow as a nest. "Each male now
mounts vigilant guard over his respective hollow, and vigorously
attacks and drives away any other fish of the same sex. Towards his
companions of the opposite sex his conduct is far different; many of
the latter are now distended with spawn, and these he endeavours by
all the means in his power to lure singly to his prepared hollow,
and there to deposit the myriad ova with which they are laden, which
he then protects and guards with the greatest care."*

  * Nature, May, 1873, p. 25.

  A more striking case of courtship, as well as of display, by the
males of a Chinese Macropus has been given by M. Carbonnier, who
carefully observed these fishes under confinement.* The males are most
beautifully coloured, more so than the females. During the
breeding-season they contend for the possession of the females; and,
in the act of courtship, expand their fins, which are spotted and
ornamented with brightly coloured rays, in the same manner,
according to M. Carbonnier, as the peacock. They then also bound about
the females with much vivacity, and appear by "l'etalage de leurs
vives couleurs chercher a attirer l'attention des femelles, lesquelles
ne paraissaient indifferentes a ce manege, elles nageaient avec une
molle lenteur vers les males et semblaient se complaire dans leur
voisinage." After the male has won his bride, he makes a little disc
of froth by blowing air and mucus out of his mouth. He then collects
the fertilised ova, dropped by the female, in his mouth; and this
caused M. Carbonnier much alarm, as he thought that they were going to
be devoured. But the male soon deposits them in the disc of froth,
afterwards guarding them, repairing the froth, and taking care of
the young when hatched. I mention these particulars because, as we
shall presently see, there are fishes, the males of which hatch
their eggs in their mouths; and those who do not believe in the
principle of gradual evolution might ask how could such a habit have
originated; but the difficulty is much diminished when we know that
there are fishes which thus collect and carry the eggs; for if delayed
by any cause in depositing them, the habit of hatching them in their
mouths might have been acquired.

  * Bulletin de la Societe d'Acclimation, Paris, July, 1869, and Jan.,
1870.

  To return to our more immediate subject. The case stands thus:
female fishes, as far as I can learn, never willingly spawn except
in the presence of the males; and the males never fertilise the ova
except in the presence of the females. The males fight for the
possession of the females. In many species, the males whilst young
resemble the females in colour; but when adult become much more
brilliant, and retain their colours throughout life. In other
species the males become brighter than the females and otherwise
more highly ornamented, only during the season of love. The males
sedulously court the females, and in one case, as we have seen, take
pains in displaying their beauty before them. Can it be believed
that they would thus act to no purpose during their courtship? And
this would be the case, unless the females exert some choice and
select those males which please or excite them most. If the female
exerts such choice, all the above facts on the ornamentation of the
males become at once intelligible by the aid of sexual selection.
  We have next to inquire whether this view of the bright colours of
certain male fishes having been acquired through sexual selection can,
through the law of the equal transmission of characters to both sexes,
be extended to those groups in which the males and females are
brilliant in the same, or nearly the same degree and manner. In such a
genus as Labrus, which includes some of the most splendid fishes in
the world- for instance, the peacock Labrus (L. pavo), described,*
with pardonable exaggeration, as formed of polished scales of gold,
encrusting lapis-lazuli, rubies, sapphires, emeralds, and amethysts-
we may, with much probability, accept this belief; for we have seen
that the sexes in at least one species of the genus differ greatly
in colour. With some fishes, as with many of the lowest animals,
splendid colours may be the direct result of the nature of their
tissues and of the surrounding conditions, without the aid of
selection of any kind. The gold-fish (Cyprinus auratus), judging
from the analogy of the golden variety of the common carp, is
perhaps a case in point, as it may owe its splendid colours to a
single abrupt variation, due to the conditions to which this fish
has been subjected under confinement. It is, however, more probable
that these colours have been intensified through artificial selection,
as this species has been carefully bred in China from a remote
period.*(2) Under natural conditions it does not seem probable that
beings so highly organised as fishes, and which live under such
complex relations, should become brilliantly coloured without
suffering some evil or receiving some benefit from so great a
change, and consequently without the intervention of natural
selection.

  * Bory de Saint Vincent, in Dict. Class. d'Hist. Nat., tom. ix.,
1826, p. 151.
  *(2) Owing to some remarks on this subject, made in my work On the
Variation of Animals under Domestication, Mr. W. F. Mayers (Chinese
Notes and Queries, Aug., 1868, p. 123) has searched the ancient
Chinese encyclopedias. He finds that gold-fish were first reared in
confinement during the Sung Dynasty, which commenced A.D. 960. In
the year 1129 these fishes abounded. In another place it is said
that since the year 1548 there has been "produced at Hangchow a
variety called the fire-fish, from its intensely red colour. It is
universally admired, and there is not a household where it is not
cultivated, in rivalry as to its colour, and as a source of profit."

  What, then, are we to conclude in regard to the many fishes, both
sexes of which are splendidly coloured? Mr. Wallace* believes that the
species which frequent reefs, where corals and other brightly-coloured
organisms abound, are brightly coloured in order to escape detection
by their enemies; but according to my recollection they were thus
rendered highly conspicuous. In the fresh-waters of the tropics
there are no brilliantly-coloured corals or other organisms for the
fishes to resemble; yet many species in the Amazons are beautifully
coloured, and many of the carnivorous Cyprinidae in India are
ornamented with "bright longitudinal lines of various tints."*(2)
Mr. M'Clelland, in describing these fishes, goes so far as to
suppose that "the peculiar brilliancy of their colours" serves as "a
better mark for king-fishers, terns, and other birds which are
destined to keep the number of these fishes in check"; but at the
present day few naturalists will admit that any animal has been made
conspicuous as an aid to its own destruction. It is possible that
certain fishes may have been rendered conspicuous in order to warn
birds and beasts of prey that they were unpalatable, as explained when
treating of caterpillars; but it is not, I believe, known that any
fish, at least any fresh-water fish, is rejected from being
distasteful to fish-devouring animals. On the whole, the most probable
view in regard to the fishes, of which both sexes are brilliantly
coloured, is that their colours were acquired by the males as a sexual
ornament, and were transferred equally, or nearly so, to the other
sex.

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