Tn] The Colors of Animals and Plants. 713 
be added, however, that the contents of the only volume as yet 
published refer chiefly to the historical development of geograph- 
ical discovery in China and Central Asia, forming by far the 
most copious and thoroughly digested summary of facts ever as 
yet presented relating to this interesting but difficult subject. 
THE COLORS OF ANIMALS AND PLANTS.? 
BY ALFRED RUSSEL WALLACE. 
I. THE COLORS OF ANIMALS. 
Theory of Sexual Colors.—In Mr. Darwin’s celebrated work, 
The Descent of Man and Selection in Relation to Sex, he has 
treated of sexual color in combination with other sexual charac- 
ters, and has arrived at the conclusion that all, or almost all, the 
colors of the higher animals (including among these insects and 
all vertebrates) are due to voluntary sexual selection ; and that 
diversity of color in the sexes is due, primarily, to the transmis- 
sion of color-variations either to one sex only, or to both sexes, 
the difference depending on some ünknowi law, and not being 
due to natural selection. 
I have long held this portion of Mr. Darwin’s theory to be er- 
roneous, and have argued that the primary cause of sexual diver- 
sity of color was the need of protection, repressing in the female 
those. os colors which are nominally produced in both sexes 
by general laws; and I have attempted to explain many of the 
more difficult cases on this principle (A Theory of Birds’ Nests, 
in Contributions, etc., page 231). As I have since given much 
thought to this sibfeot: and have arrived at some views which 
appear to me to be of considerable importance, it will be well to 
sketch briefly the theory I now hold, and afterward show its ap- 
plication to some of the detailed cases adduced in Mr Darwin’s 
work. 
The very frequent superiority of the male bird or insect in 
brightness or intensity of color, even when the general tints and 
coloration are the same, now seems to me to be due to the greater 
vigor and activity and the higher vitality of the male. The col- 
ors of an animal usually fade during disease or weakness, while 
robust health and vigor add to their intensity. This intensity of 
coloration is most manifest in the male during the breeding-sea- 
son, when the vitality is at a maximum. It is also very manifest 
1 From Macmillan’s Magazine, Concluded from page 662. 
