714 The Colors of Animals and Plants. [ December, 
in those cases in which the male is smaller than the female, as in 
the hawks and in’ most butterflies and moths. The same phe- 
nomena occur, though in a less marked degree, among mamma- 
lia. Whenever there isa difference of color between the sexes 
the male is the darker or more strongly marked, and difference 
of intensity is most visible during the breeding season (Descent 
of Man, page 533). Numerous cases among domestic animals 
also prove that there is an inherent tendency in the male to spe- 
cial developments of dermal appendages and ‘color, quite inde- 
pendently of sexual or any other form of selection. Thus, “ the 
hump on the male zebu cattle of India, the tail of fat-tailed rams, 
the arched outline of the forehead in the males of several breeds 
of sheep, and the mane, the long hairs on the hind-legs, and the 
dewlap of the male of the Berbura goat,” are all adduced by Mr. 
Darwin as instances of characters peculiar to the male, yet not 
derived from any parent ancestral form. Among domestic pig- 
eons the character of the different breeds is often most strongly 
manifested in the male birds; the wattle of the carriers and the 
eye-wattles of the barbs are largest in the males, and male pout- 
ers distend their crops to a much greater extent than do the fe- 
males, and the cock fantails often have a greater number of tail- 
feathers than the females. There are also some varieties of pig- — 
eons of which the males are striped or spotted with black, while - 
the females are never so spotted (Animals and Plants under Do- 
mestication, i., 161); yet in the parent stock of these pigeons 
there are no differences between the sexes either of plumage or _ 
color, and artificial selection has not been applied to produce — 
them. 
The greater intensity of coloration in the male — which may 
be termed the normal sexual difference — would be further de- 
veloped by the combats of the males for the possession of the fe- 
males. The most vigorous and energetic usually being able to 
rear most offspring, intensity of color, if dependent on or cor- 
related with vigor, would tend to increase. But as differences of 
color depend upon minute chemical or structural differences 1m 
the organism, increasing vigor acting unequally on different por- 
tions of the integument, and often producing at the same time 
abnormal developments of hair, horns, scales, feathers, etc., 
would almost necessarily lead also to variable distribution of oes 
color, and thus to the production of new tints and markings. 
hese acquired colors would, as Mr. Darwin has shown, be trans- 
mitted to both sexes or to one only, according as they first ap- — - 
Spans one 
