transferred exclusively to that sex, in which they first appear. Ample
evidence on this head has been advanced in my work on Variation under
Domestication, but a few instances may here be given. There are breeds
of the sheep and goat, in which the horns of the male differ greatly in
shape from those of the female; and these differences, acquired under
domestication, are regularly transmitted to the same sex. As a rule, it
is the females alone in cats which are tortoise-shell, the
corresponding colour in the males being rusty-red. With most breeds of
the fowl, the characters proper to each sex are transmitted to the same
sex alone. So general is this form of transmission that it is an
anomaly when variations in certain breeds are transmitted equally to
both sexes. There are also certain sub-breeds of the fowl in which the
males can hardly be distinguished from one another, whilst the females
differ considerably in colour. The sexes of the pigeon in the
parent-species do not differ in any external character; nevertheless,
in certain domesticated breeds the male is coloured differently from
the female. (36. Dr. Chapuis, Le Pigeon Voyageur Belge, 1865, p. 87.
Boitard et Corbie, Les Pigeons de Voliere, etc., 1824, p. 173. See,
also, on similar differences in certain breeds at Modena, Le
variazioni dei Colombi domestici, del Paolo Bonizzi, 1873.) The wattle
in the English Carrier pigeon, and the crop in the Pouter, are more
highly developed in the male than in the female; and although these
characters have been gained through long-continued selection by man,
the slight differences between the sexes are wholly due to the form of
inheritance which has prevailed; for they have arisen, not from, but
rather in opposition to, the wish of the breeder.
Most of our domestic races have been formed by the accumulation of many
slight variations; and as some of the successive steps have been
transmitted to one sex alone, and some to both sexes, we find in the
different breeds of the same species all gradations between great
sexual dissimilarity and complete similarity. Instances have already
been given with the breeds of the fowl and pigeon, and under nature
analogous cases are common. With animals under domestication, but
whether in nature I will not venture to say, one sex may lose
characters proper to it, and may thus come somewhat to resemble the
opposite sex; for instance, the males of some breeds of the fowl have
lost their masculine tail-plumes and hackles. On the other hand, the
differences between the sexes may be increased under domestication, as
with merino sheep, in which the ewes have lost their horns. Again,
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