History of the World/History of the World (Bureau Development, Inc.)(1992).BIN/dp/0109/01096.txt

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$Unique_ID{how01096}
$Pretitle{}
$Title{Descent Of Man, The
Chapter 16.1}
$Subtitle{}
$Author{Darwin, Charles}
$Affiliation{}
$Subject{young
species
female
females
male
plumage
adult
sexes
males
birds}
$Date{1874}
$Log{}
Title:       Descent Of Man, The
Book:        Part II: Sexual Selection
Author:      Darwin, Charles
Date:        1874

Chapter 16.1

     The immature plumage in relation to the character of the plumage in both
sexes when adult - Six classes of cases - Sexual differences between the males
of closely allied or representative species - The female assuming the
characters of the male - Plumage of the young in relation to the summer and
winter plumage of the adults - On the increase of beauty in the birds of the
world - Protective coloring - Conspicuously colored birds - Novelty
appreciated - Summary of the four chapters on birds.

     We must now consider the transmission of characters as limited by age, in
reference to sexual selection.  The truth and importance of the principle of
inheritance at corresponding ages need not here be discussed, as enough has
already been said on the subject.  Before giving the several rather complex
rules or classes of cases under which the differences in plumage between the
young and the old, as far as known to me, may be included, it will be well to
make a few preliminary remarks.

     With animals of all kinds, when the adults differ in color from the
young, and the colors of the latter are not, as far as we can see, of any
special service, they may generally be attributed, like various embryological
structures, to the retention of a former character.  But this view can be
maintained with confidence only when the young of several species resemble
each other closely, and likewise resemble other adult species belonging to the
same group; for the latter are the living proofs that such a state of things
was formerly possible.  Young lions and pumas are marked with feeble stripes
or rows of spots, and as many allied species both young and old are similarly
marked no believer in evolution will doubt that the progenitor of the lion and
puma was a striped animal, and that the young have retained vestiges of the
stripes like the kittens of black cats, which are not in the least striped
when grown up.  Many species of deer, which when mature are not spotted, are
while young covered with white spots, as are likewise some few species in the
adult state.  So again the young in the whole family of pigs (Suidae), and in
certain rather distantly allied animals, such as the tapir, are marked with
dark longitudinal stripes; but here we have a character apparently derived
from an extinct progenitor, and now preserved by the young alone.  In all such
cases the old have had their colors changed in the course of time, while the
young have remained but little altered, and this has been effected through the
principle of inheritance at corresponding ages.

     This same principle applies to many birds belonging to various groups in
which the young closely resemble each other, and differ much from their
respective adult parents.  The young of almost all the Gallinaceae and of some
distantly allied birds, such as ostriches, are covered with longitudinally
striped down; but this character points back to a state of things so remote
that it hardly concerns us.  Young cross-bills (Loxia) have at first straight
beaks like those of other finches, and in their immature striated plumage they
resemble the mature redpole and female siskin, as well as the young of the
goldfinch, greenfinch and some other allied species.  The young of many kinds
of buntings (Emberiza) resemble one another, and likewise the adult states of
the common bunting, E. miliaria.  In almost the whole large group of thrushes
the young have their breasts spotted - a character which is retained
throughout life by many species, but is quite lost by others, as by the Turdus
migratorius.  So again with many thrushes, the feathers on the back are
mottled before they are moulted for the first time, and this character is
retained for life by certain eastern species.  The young of many species of
shrikes (Lanius), of some woodpeckers and of an Indian pigeon (Chalcophaps
indicus) are transversely striped on the under surface; and certain allied
species or whole genera are similarly marked when adult.  In some closely
allied and resplendent Indian cuckoos (Chrysococcyx) the mature species differ
considerably from one another in color, but the young cannot be distinguished.
The young of an Indian goose (Sarkidiornis melanonotus) closely resemble in
plumage an allied genus, Dendrocygna, when mature. ^926 Similar facts will
hereafter be given in regard to certain herons.  Young black grouse (Tetrao
tetrix) resemble the young as well as the old of certain other species, for
instance, the red grouse or T. scoticus.  Finally, as Mr. Blyth, who has
attended closely to this subject, has well remarked, the natural affinities of
many species are best exhibited in their immature plumage; and as the true
affinities of all organic beings depend on their descent from a common
progenitor, this remark strongly confirms the belief that the immature plumage
approximately shows us the former or ancestral condition of the species.

[Footnote 926: In regard to thrushes, shrikes and woodpeckers, see Mr. Blyth,
in Charlesworth's "Mag. of Nat. Hist.," vol. i, 1837, p. 304; also foot-note
to his translation of Cuvier's "Regne Animal," p. 159.  I give the case of
Loxia on Mr. Blyth's information.  On thrushes, see also Audubon, "Ornith.
Biography," vol. ii, p. 195.  On Chrysococcyx and Chalcophaps, Blyth, as
quoted in Jerdon's "Birds of India," vol. iii, p. 485.  On Sarkidiornis,
Blyth, in "Ibis," 1867, p. 175.]

     Although many young birds belonging to various families thus give us a
glimpse of the plumage of their remote progenitors, yet there are many other
birds, both dull-colored and bright-colored, in which the young closely
resemble their parents.  In such cases the young of the different species
cannot resemble each other more closely than do the parents; nor can they
strikingly resemble allied forms when adult.  They give us but little insight
into the plumage of their progenitors, excepting in so far that when the young
and the old are colored in the same general manner throughout a whole group of
species, it is probable that their progenitors were similarly colored.

     We may now consider the classes of cases under which the differences and
resemblances between the plumage of the young and the old, in both sexes or in
one sex alone, may be grouped.  Rules of this kind were first enounced by
Cuvier; but with the progress of knowledge they require some modification and
amplification.  This I have attempted to do, as far as the extreme complexity
of the subject permits, from information derived from various sources; but a
full essay on this subject by some competent ornithologist is much needed.  In
order to ascertain to what extent each rule prevails I have tabulated the
facts given in four great works, namely, by Macgillivray on the birds of
Britain, Audubon on those of North America, Jerdon on those of India, and
Gould on those of Australia. I may here premise, first, that the several cases
or rules graduate into each other; and secondly, that when the young are said
to resemble their parents it is not meant that they are identically alike, for
their colors are almost always less vivid, and the feathers are softer and
often of a different shape.

Rules Or Classes Of Cases.

     I.  When the adult male is more beautiful or conspicuous than the adult
female, the young of both sexes in their first plumage closely resemble the
adult female, as with the common fowl and peacock; or, as occasionally occurs,
they resemble her much more closely than they do the adult male.

     II.  When the adult female is more conspicuous than the adult male, as
sometimes, though rarely, occurs, the young of both sexes in their first
plumage resemble the adult male.

     III.  When the adult male resembles the adult female, the young of both
sexes have a peculiar first plumage of their own, as with the robin.

     IV.  When the adult male resembles the adult female, the young of both
sexes in their first plumage resemble the adults, as with the kingfisher, many
parrots, crows, hedgewarblers.

     V.  When the adult of both sexes have a distinct winter and summer
plumage, whether or not the male differs from the female, the young resemble
the adults of both sexes in their winter dress, or much more rarely in their
summer dress, or they resemble the females alone.  Or the young may have an
intermediate character; or again they may differ greatly from the adults in
both their seasonal plumages.

     VI.  In some few cases the young in their first plumage differ from each
other according to sex; the young males resembling more or less closely the
adult males, and the young females more or less closely the adult females.

     Class I. - In this class the young of both sexes more or less closely
resemble the adult female, while the adult male differs from the adult female,
often in the most conspicuous manner.  Innumerable instances in all orders
could be given; it will suffice to call to mind the common pheasant, duck and
house-sparrow.  The cases under this class graduate into others.  Thus the two
sexes when adult may differ so slightly, and the young so slightly from the
adults, that it is doubtful whether such cases ought to come under the
present, or under the third or fourth classes.  So, again, the young of the
two sexes, instead of being quite alike, may differ in a slight degree from
each other, as in our sixth class.  These transitional cases, however, are
few, or at least are not strongly pronounced, in comparison with those which
come strictly under the present class.

     The force of the present law is well shown in those groups, in which, as
a general rule, the two sexes and the young are all alike; for when in these
groups the male does differ from the female, as with certain parrots,
kingfishers, pigeons, etc., the young of both sexes resemble the adult female.
^927 We see the same fact exhibited still more clearly in certain anomalous
cases; thus the male of Heliothrix auriculata (one of the humming-birds)
differs conspicuously from the female in having a splendid gorget and fine
ear-tufts, but the female is remarkable from having a much longer tail than
that of the male; now the young of both sexes resemble (with the exception of
the breast being spotted with bronze) the adult female in all other respects,
including the length of her tail, so that the tail of the male actually
becomes shorter as he reaches maturity, which is a most unusual circumstance.
^928 Again, the plumage of the male goosander (Mergus merganser) is more
conspicuously colored than that of the female, with the scapular and secondary
wing-feathers much longer; but differently from what occurs, as far as I know
in any other bird, the crest of the adult male, though broader than that of
the female, is considerably shorter, being only a little above an inch in
length; the crest of the female being two and a half inches long.  Now the
young of both sexes entirely resemble the adult female, so that their crests
are actually of greater length, though narrower than in the adult male. ^929

[Footnote 927: See, for instance, Mr. Gould's account ("Hand-book to the Birds
of Australia" vol. i, p. 133) of Cyanalcyon (one of the kingfishers), in
which, however, the young male, though resembling the adult female, is less
brilliantly colored.  In some species of Dacelo the males have blue tails, and
the females brown ones; and Mr. R. B. Sharpe informs me that the tail of the
young male of D. gaudichaudi is at first brown.  Mr. Gould has described
(ibid, vol. ii, pp. 14, 20, 37) the sexes and the young of certain black
cockatoos and of the King Lory, with which the same rule prevails.  Also
Jerdon ("Birds of India," vol. i, p. 260) on the Paloeornis rosa, in which the
young are more like the female than the male.  See Audubon ("Ornith.
Biograph.," vol. ii, p. 475) on the two sexes and the young of Columba
passerina.]

[Footnote 928: I owe this information to Mr. Gould, who showed me the
specimens; see also his "Introduction to the Trochilidae," 1861, p. 120.]

[Footnote 929: Macgillivray, "Hist. Brit. Birds," vol. v, pp. 207, 214.]

     When the young and the females closely resemble each other and both
differ from the males, the most obvious conclusion is that the males alone
have been modified.  Even in the anomalous cases of the Heliothrix and Mergus,
it is probable that originally both adult sexes were furnished - the one
species with a much elongated tail and the other with a much elongated crest -
these characters having since been partially lost by the adult males from some
unexplained cause, and transmitted in their diminished state to their male
offspring alone, when arrived at the corresponding age of maturity.  The
belief that in the present class the male alone has been modified, as far as
the differences between the male and the female together with her young are
concerned, is strongly supported by some remarkable facts recorded by Mr.
Blyth, ^930 with respect to closely allied species which represent each other
in distinct countries.  For with several of these representative species the
adult males have undergone a certain amount of change and can be
distinguished; the females and the young from the distinct countries being
indistinguishable, and therefore absolutely unchanged.  This is the case with
certain Indian chats (Thamnobia), with certain honey-suckers (Nectarinia),
shrikes (Tephrodornis), certain kingfishers (Tanysiptera), Kalij pheasants
(Gallophasis) and tree-partridges (Arboricola).

[Footnote 930: See his admirable paper in the "Journal of the Asiatic Soc. of
Bengal," vol xix, 1850, p. 223; see also Jerdon, "Birds of India," vol. i,
introduction, p. 29.  In regard to Tanysiptera, Prof. Schlegel told Mr. Blyth
that he could distinguish several distinct races, solely by comparing the
adult males.]

     In some analogous cases, namely, with birds having a different summer and
winter plumage, but with the two sexes nearly alike, certain closely allied
species can easily be distinguished in their summer or nuptial plumage, yet
are indistinguishable in their winter as well as in their immature plumage.
This is the case with some of the closely allied Indian wag-tails or
Motacillae.  Mr. Swinhoe ^931 informs me that three species of Ardeola, a
genus of herons, which represent one another on separate continents, are "most
strikingly different" when ornamented with their summer plumes, but are
hardly, if at all, distinguishable during the winter.  The young also of these
three species in their immature plumage closely resemble the adults in their
winter dress.  This case is all the more interesting, because with two other
species of Ardeola both sexes retain, during the winter and summer, nearly the
same plumage as that possessed by the three first species during the winter
and in their immature state; and this plumage, which is common to several
distinct species at different ages and seasons, probably shows us how the
progenitors of the genus were colored.  In all these cases, the nuptial
plumage which we may assume was originally acquired by the adult males during
the breeding-season, and transmitted to the adults of both sexes at the
corresponding season, has been modified, while the winter and immature
plumages have been left unchanged.

[Footnote 931: See also Mr. Swinhoe, in "Ibis," July, 1863, p. 131; and a
previous paper, with an extract from a note by Mr. Blyth, in "Ibis," Jan.
1861, p. 24.]

     The question naturally arises, how is it that in these latter cases the
winter plumage of both sexes, and in the former cases the plumage of the adult
females, as well as the immature plumage of the young, have not been at all
affected?  The species which represent each other in distinct countries will
almost always have been exposed to somewhat different conditions, but we can
hardly attribute to this action the modification of the plumage in the males
alone, seeing that the females and the young, though similarly exposed, have
not been affected.  Hardly any fact shows us more clearly how subordinate in
importance is the direct action of the conditions of life, in comparison with
the accumulation through selection of indefinite variations, than the
surprising difference between the sexes of many birds; for both will have
consumed the same food, and have been exposed to the same climate.
Nevertheless we are not precluded from believing that in the course of time
new conditions may produce some direct effect either on both sexes, or from
their constitutional differences chiefly on one sex.  We see only that this is
subordinate in importance to the accumulated results of selection.  Judging,
however, from a wide-spread analogy, when a species migrates into a new
country (and this must precede the formation of representative species), the
changed conditions to which they will almost always have been exposed will
cause them to undergo a certain amount of fluctuating variability. In this
case sexual selection, which depends on an element liable to change - the
taste or admiration of the female - will have had new shades of color or other
differences to act on and accumulate; and as sexual selection is always at
work, it would (from what we know of the results on domestic animals of man's
unintentional selection) be surprising if animals inhabiting separate
districts, which can never cross and thus blend their newly acquired
characters, were not, after a sufficient lapse of time, differently modified.
These remarks likewise apply to the nuptial or summer plumage, whether
confined to the males or common to both sexes.

     Although the females of the above closely allied or representative
species, together with their young, differ hardly at all from one another, so
that the males alone can be distinguished, yet the females of most species
within the same genus obviously differ from each other.  The differences,
however, are rarely as great as between the males.  We see this clearly in the
whole family of the Gallinaceae; the females, for instance, of the common and
Japan pheasant, and especially of the gold and Amherst pheasant - of the
silver pheasant and the wild fowl - resemble one another very closely in
color, while the males differ to an extraordinary degree.  So it is with the
females of most of the Cotingidae, Fringillidae, and many other families.
There can indeed be no doubt that, as a general rule, the females have been
less modified than the males.  Some few birds, however, offer a singular and
inexplicable exception; thus the females of Paradisea apoda and P. papuana
differ from each other more than do their respective males; ^932 the female of
the latter species having the under surface pure white, while the female P.
apoda is deep brown beneath.  So, again, as I hear from Prof. Newton, the
males of two species of Oxynotus (shrikes), which represent each other in the
Islands of Mauritius and Bourbon, ^933 differ but little in color, while the
females differ much.  In the Bourbon species the female appears to have
partially retained an immature condition of plumage, for at first sight she
"might be taken for the young of the Mauritian species." These differences may
be compared with those inexplicable ones which occur independently of man's
selection in certain sub-breeds of the game-fowl, in which the females are
very different, while the males can hardly be distinguished. ^934

[Footnote 932: Wallace, "The Malay Archipelago," vol. ii, 1869, p. 394.]

[Footnote 933: These species are described with colored figures, by M. F.
Pollen, in "Ibis," 1866, p. 275.]

[Footnote 934: "Variation of Animals, etc., under Domestication," vol. i, p.
251.]

     As I account so largely by sexual selection for the differences between
the males of allied species, how can the differences between the females be
accounted for in all ordinary cases?  We need not here consider the species
which belong to distinct genera; for with these, adaptation to different
habits of life, and other agencies, will have come into play.  In regard to
the differences between the females within the same genus it appears to me
almost certain, after looking through various large groups, that the chief
agent has been the greater or less transference to the female of the
characters acquired by the males through sexual selection.  In the several
British finches the two sexes differ either very slightly or considerably; and
if we compare the females of the greenfinch, chaffinch, goldfinch, bullfinch,
crossbill, sparrow, etc., we shall see that they differ from one another
chiefly in the points in which they partially resemble their respective males;
and the colors of the males may safely be attributed to sexual selection. With
many gallinaceous species the sexes differ to an extreme degree, as with the
peacock, pheasant and fowl, while with other species there has been a partial
or even complete transference of character from the male to the female.  The
females of the several species of Polyplectron exhibit in a dim condition, and
chiefly on the tail, the splendid ocelli of their males.  The female partridge
differs from the male only in the red mark on her breast being smaller; and
the female wild turkey only in her colors being much duller.  In the
guinea-fowl the two sexes are indistinguishable.  There is no improbability in
the plain, though peculiarly spotted, plumage of this latter bird having been
acquired through sexual selection by the males, and then transmitted to both
sexes; for it is not essentially different from the much more beautifully
spotted plumage, characteristic of the males alone of the Tragopan pheasants.

     It should be observed that in some instances the transference of
characters from the male to the female has been effected apparently at a
remote period, the male having subsequently undergone great changes without
transferring to the female any of his later gained characters. For instance,
the female and the young of the black grouse (Tetrao tetrix) resemble pretty
closely both sexes and the young of the red grouse (T. scoticus); and we may
consequently infer that the black grouse is descended from some ancient
species, of which both sexes were colored in nearly the same manner as the red
grouse.  As both sexes of this latter species are more distinctly barred
during the breeding-season than at any other time, and as the male differs
slightly from the female in his more strongly pronounced red and brown tints,
^935 we may conclude that his plumage has been influenced by sexual selection,
at least to a certain extent.  If so, we may further infer that the nearly
similar plumage of the female black grouse was similarly produced at some
former period.  But since this period the male black grouse has acquired his
fine black plumage with his forked and outwardly curled tail-feathers; but of
these characters there has hardly been any transference to the female,
excepting that she shows in her tail a trace of the curved fork.

[Footnote 935: Macgillivray, "Hist. British Birds," vol. i, pp. 172-174.]

     We may therefore conclude that the females of distinct though allied
species have often had their plumage rendered more or less different by the
transference of various degrees of characters acquired by the males through
sexual selection both during former and recent times.  But it deserves
especial attention that brilliant colors have been transferred much more
rarely than other tints.  For instance, the male of the red-throated
blue-breast (Cyanecula suecica) has a rich blue breast, including a
sub-triangular red mark; now marks of nearly the same shape have been
transferred to the female, but the central space is fulvous instead of red and
is surrounded by mottled instead of blue feathers. The Gallinaceae offer many
analogous cases; for none of the species, such as partridges, quails,
guinea-fowl, etc., in which the colors of the plumage have been largely
transferred from the male to the female, are brilliantly colored.  This is
well exemplified with the pheasants, in which the male is generally so much
more brilliant than the female; but with the eared and cheer pheasants
(Crossoptilon auritum and Phasianus wallichii) the sexes closely resemble each
other and their colors are dull.  We may go so far as to believe that if any
part of the plumage in the males of these two pheasants had been brilliantly
colored it would not have been transferred to the females.  These facts
strongly support Mr. Wallace's view that with birds which are exposed to much
danger during incubation, the transference of bright colors from the male to
the female has been checked through natural selection.  We must not, however,
forget that another explanation, before given, is possible; namely, that the
males which varied and became bright, while they were young and inexperienced,
would have been exposed to much danger and would generally have been
destroyed; the older and more cautious males, on the other hand, if they
varied in a like manner, would not only have been able to survive, but would
have been favored in their rivalry with other males. Now variations occurring
late in life tend to be transmitted exclusively to the same sex, so that in
this case extremely bright tints would not have been transmitted to the
females.  On the other hand, ornaments of a less conspicuous kind, such as
those possessed by the eared and cheer pheasants, would not have been
dangerous, and if they appeared during early youth would generally have been
transmitted to both sexes.

     In addition to the effects of the partial transference of characters from
the males to the females some of the differences between the females of
closely allied species may be attributed to the direct or definite action of
the conditions of life. ^936 With the males any such action would generally
have been masked by the brilliant colors gained through sexual selection; but
not so with the females.  Each of the endless diversities in plumage which we
see in our domesticated birds is, of course, the result of some definite
cause; and, under natural and more uniform conditions, some one tint, assuming
that it was in no way injurious, would almost certainly sooner or later
prevail.  The free intercrossing of the many individuals belonging to the same
species would ultimately tend to make any change of color thus induced uniform
in character.

[Footnote 936: See, on this subject, chap. xxiii, in the "Variation of Animals
and Plants under Domestication."]

     No one doubts that both sexes of many birds have had their colors adapted
for the sake of protection; and it is possible that the females alone of some
species may have been modified for this end.  Although it would be a
difficult, perhaps an impossible, process, as shown in the last chapter, to
convert one form of transmission into another through selection, there would
not be the least difficulty in adapting the colors of the female,
independently of those of the male, to surrounding objects, through the
accumulation of variations which were from the first limited in their
transmission to the female sex.  If the variations were not thus limited the
bright tints of the male would be deteriorated or destroyed.  Whether the
females alone of many species have been thus specially modified is at present
very doubtful.  I wish I could follow Mr. Wallace to the full extent; for the
admission would remove some difficulties.  Any variations which were of no
service to the female as a protection would be at once obliterated, instead of
being lost simply by not being selected, or from free intercrossing, or from
being eliminated when transferred to the male and in any way injurious to him.
Thus the plumage of the female would be kept constant in character.  It would
also be a relief if we could admit that the obscure tints of both sexes of
many birds had been acquired and preserved for the sake of protection, for
example, of the hedge-warbler or kitty-wren (Accentor modularis and
Troglodytes vulgaris), with respect to which we have no sufficient evidence of
the action of sexual selection.  We ought, however, to be cautious in
concluding that colors which appear to us dull are not attractive to the
females of certain species; we should bear in mind such cases as that of the
common house-sparrow, in which the male differs much from the female, but does
not exhibit any bright tints.  No one probably will dispute that many
gallinaceous birds which live on the open ground have acquired their present
colors, at least in part, for the sake of protection.  We know how well they
are thus concealed; we know that ptarmigans, while changing from their winter
to their summer plumage, both of which are protective, suffer greatly from
birds of prey.  But can we believe that the very slight differences in tints
and markings between, for instance, the female black-grouse and red-grouse
serve as a protection?  Are partridges, as they are now colored, better
protected than if they had resembled quails?  Do the slight differences
between the females of the common pheasant, the Japan and gold pheasants,
serve as a protection, or might not their plumages have been interchanged with
impunity?  From what Mr. Wallace has observed of the habits of certain
gallinaceous birds in the east, he thinks that such slight differences are
beneficial.  For myself, I will only say that I am not convinced.

     Formerly when I was inclined to lay much stress on protection as
accounting for the duller colors of female birds, it occurred to me that
possibly both sexes and the young might aboriginally have been equally bright
colored; but that subsequently, the females from the danger incurred during
incubation, and the young from being inexperienced, had been rendered dull as
a protection.  But this view is not supported by any evidence, and is not
probable; for we thus in imagination expose during past times the females and
the young to danger, from which it has subsequently been necessary to shield
their modified descendants.  We have, also, to reduce, through a gradual
process of selection, the females and the young to almost exactly the same
tints and markings, and to transmit them to the corresponding sex and period
of life.  On the supposition that the females and the young have partaken
during each stage of the process of modification of a tendency to be as
brightly colored as the males, it is also a somewhat strange fact that the
females have never been rendered dull colored without the young participating
in the same change; for there are no instances, as far as I can discover, of
species with the females dull and the young bright colored.  A partial
exception, however, is offered by the young of certain woodpeckers, for they
have "the whole upper part of the head tinged with red," which afterward
either decreases into a mere circular red line in the adults of both sexes, or
quite disappears in the adult females. ^937

[Footnote 937: Audubon, "Ornith.  Biography," vol. i, p. 193. Macgillivray,
"Hist. Brit. Birds," vol. iii, p. 85.  See also the case before given of
Indopicus carlotta.]

     Finally, with respect to our present class of cases, the most probable
view appears to be that successive variations in brightness or in other
ornamental characters occurring in the males at a rather late period of life
have alone been preserved; and that most or all of these variations, owing to
the late period of life at which they appeared, have been from the first
transmitted only to the adult male offspring.  Any variations in brightness
occurring in the females or in the young would have been of no service to
them, and would not have been selected; and moreover, if dangerous would have
been eliminated.  Thus the females and the young will either have been left
unmodified, or (as is much more common) will have been partially modified by
receiving through transference from the males some of his successive
variations.  Both sexes have perhaps been directly acted on by the conditions
of life to which they have long been exposed; but the females from not being
otherwise much modified will best exhibit any such effects.  These changes and
all others will have been kept uniform by the free intercrossing of many
individuals.  In some cases, especially with ground birds, the females and the
young may possibly have been modified, independently of the males, for the
sake of protection so as to have acquired the same dull-colored plumage.

     Class II.  When the adult female is more conspicuous than the adult male
the young of both sexes in their first plumage resemble the adult male. - This
class is exactly the reverse of the last, for the females are here brighter
colored or more conspicuous than the males; and the young, as far as they are
known, resemble the adult males instead of the adult females.  But the
difference between the sexes is never nearly so great as with many birds in
the first class, and the cases are comparatively rare.  Mr. Wallace, who first
called attention to the singular relation which exists between the less bright
colors of the males and their performing the duties of incubation, lays great
stress on this point ^938 as a crucial test that obscure colors have been
acquired for the sake of protection during the period of nesting.  A different
view seems to me more probable.  As the cases are curious and not numerous I
will briefly give all that I have been able to find.

[Footnote 938: "Westminster Review," July, 1867, and A. Murray, "Journal of
Travel," 1868, p. 83.]

     In one section of the genus Turnix, quail-like birds, the female is
invariably larger than the male (being nearly twice as large in one of the
Australian species), and this is an unusual circumstance with the Gallinaceae.
In most of the species the female is more distinctly colored and brighter than
the male, ^939 but in some few species the sexes are alike.  In Turnix taigoor
of India the male "wants the black on the throat and neck, and the whole tone
of the plumage is lighter and less pronounced than that of the female." The
female appears to be noisier, and is certainly much more pugnacious than the
male; so that the females and not the males are often kept by the natives for
fighting, like gamecocks.  As male birds are exposed by the English
bird-catchers for a decoy near a trap, in order to catch other males by
exciting their rivalry, so the females of this Turnix are employed in India.
When thus exposed the females soon begin their "loud, purring call, which can
be heard a long way off, and any females within ear-shot run rapidly to the
spot and commence fighting with the caged bird." In this way from twelve to
twenty birds, all breeding-females, may be caught in the course of a single
day.  The natives assert that the females after laying their eggs associate in
flocks, and leave the males to sit on them.  There is no reason to doubt the
truth of this assertion, which is supported by some observations made in China
by Mr. Swinhoe. ^940 Mr. Blyth believes that the young of both sexes resemble
the adult male.

[Footnote 939: For the Australian species, see Gould's "Hand-book," etc., vol.
ii, pp. 178, 180, 186, 188.  In the British Museum specimens of the Australian
Plain-wanderer (Pedionomus torquatus) may be seen, showing similar sexual
differences.]

[Footnote 940: Jerdon, "Birds of India," vol. iii, p. 596.  Mr. Swinhoe, in
"Ibis," 1865, p. 542; 1866, pp. 131, 405.]

     The females of the three species of painted snipes (Rhynchaea, fig. 62)
"are not only larger but much more richly colored than the males." ^941 With
all other birds in which the trachea differs in structure in the two sexes it
is more developed and complex in the male than in the female; but in the
Rhynchaea australis it is simple in the male, while in the female it makes
four distinct convolutions before entering the lungs. ^942 The female,
therefore, of this species has acquired an eminently masculine character.  Mr.
Blyth ascertained, by examining many specimens, that the trachea is not
convoluted in either sex of R. bengalensis, which species resembles R.
australis so closely that it can hardly be distinguished except by its shorter
toes.  This fact is another striking instance of the law that secondary sexual
characters are often widely different in closely allied forms, though it is a
very rare circumstance when such differences relate to the female sex.  The
young of both sexes of R. bengalensis in their first plumage are said to
resemble the mature male. ^943 There is also reason to believe that the male
undertakes the duty of incubation, for Mr. Swinhoe ^944 found the females
before the close of the summer associated in flocks, as occurs with the
females of the Turnix.

[Footnote 941: Jerdon, "Birds of India," vol. iii, p. 677.]

[Footnote 942: Gould's "Hand-book to the Birds of Australia," vol. ii, p.
275.]

[Footnote 943: "The Indian Field," Sept., 1858, p. 3.]

[Footnote 944: "Ibis," 1866, p. 298.]