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Bullseye
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* Dr. Chapius, Le Pigeon Voyageur Belge, 1865, p. 87.
*(2) The Field, Sept., 1872.
With fowls, variations of colour, limited in their transmission to
the male sex, habitually occur. When this form of inheritance
prevails, it might well happen that some of the successive
variations would be transferred to the female, who would then slightly
resemble the male, as actually occurs in some breeds. Or again, the
greater number, but not all, of the successive steps might be
transferred to both sexes, and the female would then closely
resemble the male. There can hardly be a doubt that this is the
cause of the male pouter pigeon having a somewhat larger crop, and
of the male carrier pigeon having somewhat larger wattles, than
their respective females; for fanciers have not selected one sex
more than the other, and have had no wish that these characters should
be more strongly displayed in the male than in the female, yet this is
the case with both breeds.
The same process would have to be followed, and the same
difficulties encountered, if it were desired to make a breed with
the females alone of some new colour.
Lastly, our fancier might wish to make a breed with the two sexes
differing from each other, and both from the parent species. Here
the difficulty would be extreme, unless the successive variations were
from the first sexually limited on both sides, and then there would be
no difficulty. We see this with the fowl; thus the two sexes of the
pencilled Hamburghs differ greatly from each other, and from the two
sexes of the aboriginal Gallus bankiva; and both are now kept constant
to their standard of excellence by continued selection, which would be
impossible unless the distinctive characters of both were limited in
their transmission.
The Spanish fowl offers a more curious case; the male has an immense
comb, but some of the successive variations, by the accumulation of
which it was acquired, appear to have been transferred to the
female; for she has a comb many times larger than that of the
females of the parent species. But the comb of the female differs in
one respect from that of the male, for it is apt to lop over; and
within a recent period it has been ordered by the fancy that this
should always be the case, and success has quickly followed the order.
Now the lopping of the comb must be sexually limited in its
transmission, otherwise it would prevent the comb of the male from
being perfectly upright, which would be abhorrent to every fancier. On
the other hand, the uprightness of the comb in the male must
likewise be a sexually-limited character, otherwise it would prevent
the comb of the female from lopping over.
From the foregoing illustrations, we see that even with almost
unlimited time at command, it would be an extremely difficult and
complex, perhaps an impossible process, to change one form of
transmission into the other through selection. Therefore, without
distinct evidence in each case, I am unwilling to admit that this
has been effected in natural species. On the other hand, by means of
successive variations, which were from the first sexually limited in
their transmission, there would not be the least difficulty in
rendering a male bird widely different in colour or in any other
character from the female; the latter being left unaltered, or
slightly altered, or specially modified for the sake of protection.
As bright colours are of service to the males in their rivalry
with other males, such colours would be selected whether or not they
were transmitted exclusively to the same sex. Consequently the females
might be expected often to partake of the brightness of the males to a
greater or less degree; and this occurs with a host of species. If all
the successive variations were transmitted equally to both sexes,
the females would be indistinguishable from the males; and this
likewise occurs with many birds. If, however, dull colours were of
high importance for the safety of the female during incubation, as
with many ground birds, the females which varied in brightness, or
which received through inheritance from the males any marked accession
of brightness, would sooner or later be destroyed. But the tendency in
the males to continue for an indefinite period transmitting to their
female offspring their own brightness, would have to be eliminated
by a change in the form of inheritance; and this, as shewn by our
previous illustration, would be extremely difficult. The more probable
result of the long-continued destruction of the more brightly-coloured
females, supposing the equal form of transmission to prevail would
be the lessening or annihilation of the bright colours of the males,
owing to their continual crossing with the duller females. It would be
tedious to follow out all the other possible results; but I may remind
the reader that if sexually limited variations in brightness
occurred in the females, even if they were not in the least
injurious to them and consequently were not eliminated, yet they would
not be favoured or selected, for the male usually accepts any
female, and does not select the more attractive individuals;
consequently these variations would be liable to be lost, and would
have little influence on the character of the race; and this will
aid in accounting for the females being commonly duller-coloured
than the males.
In the eighth chapter instances were given, to which many might here
be added, of variations occurring at various ages, and inherited at
the corresponding age. It was also shewn that variations which occur
late in life are commonly transmitted to the same sex in which they
first appear; whilst variations occurring early in life are apt to
be transmitted to both sexes; not that all the cases of
sexually-limited transmission can thus be accounted for. It was
further shewn that if a male bird varied by becoming brighter whilst
young, such variations would be of no service until the age for
reproduction had arrived, and there was competition between rival
males. But in the case of birds living on the ground and commonly in
need of the protection of dull colours, bright tints would be far more
dangerous to the young and inexperienced than to the adult males.
Consequently the males which varied in brightness whilst young would
suffer much destruction and be eliminated through natural selection;
on the other hand, the males which varied in this manner when nearly
mature, notwithstanding that they were exposed to some additional
danger, might survive, and from being favoured through sexual
selection, would procreate their kind. As a relation often exists
between the period of variation and the form of transmission, if the
bright-coloured young males were destroyed and the mature ones were
successful in their courtship, the males alone would 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* 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.
* Bechstein, Naturgeschichte Deutschlands, 1793, B. iii., 339.
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 they construct a different sort of nest from that made by their
nearest allies, and not liable to be injured by their spurs; so that
the spurs have not been removed? Or are we to suppose that the females
of these several species especially require spurs for their defence?
It is a more probable conclusion that both the presence and absence of
spurs in the females result from different laws of inheritance
having prevailed, independently of natural selection. With the many
females in which spurs appear as rudiments, we may conclude that
some few of the successive variations, through which they were
developed in the males, occurred very early in life, and were
consequently transferred to the females. In the other and much rarer
cases, in which the females possess fully developed spurs, we may
conclude that all the successive variations were transferred to
them; and that they gradually acquired and inherited the habit of
not disturbing their nests.
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