274 
DARWINISM 
CIIAP. 
as types—the two sexes are nearly alike, the male being 
sometimes more intensely coloured and with fewer pale 
markings ; but in the American groups—represented by P. 
seneas, P. sesostris, and allies—there is a wonderful diversity, 
the males having a rich green or bluish patch on the fore wings, 
while the females have a band or spots of pure white, not 
always corresponding in position to the green spot of the 
males. There are, however, transitional forms, by which a 
complete series can be traced, from close similarity to great 
diversity of colouring between the sexes ; and this may perhaps 
be only an extreme example of the intenser colour and more 
concentrated markings which are a very prevalent character¬ 
istic of male butterflies. 
There are, in fact, many indications of a regular succession 
of tints in which colour development has occurred in the 
various groups of butterflies, from an original grayish or 
brownish neutral tint. Thus in the “ AEneas ” group of 
Papilios we have the patch on the upper wings yellowish in 
P. triopas, olivaceous in P. bolivar, bronzy-gray with a white 
spot in P. erlaces, more greenish and buff’ in P. iphidamas, 
gradually changing to the fine blue of P. brissonius, and the 
magnificent green of P. sesostris. In like manner, the intense 
crimson spots of the lower wings can be traced step by step 
from a yellow or buff’ tint, which is one of the most wide¬ 
spread colours in the whole order. The greater purity and 
intensity of colour seem to be usually associated with more 
pointed wings, indicating greater vigour and more rapid flight. 
Sexual Selection as a supposed Cause of Colour Development. 
Mr. Darwin, as is Avell known, imputed most of the 
brilliant colours and varied patterns of butterflies’ wings to 
sexual selection—that is, to a constant preference, by female 
butterflies, for the more brilliant males; the colours thus 
produced being sometimes transmitted to the males alone, 
sometimes to both sexes. This view has always seemed to 
me to be unsupported by evidence, while it is also quite 
inadequate to account for the facts. The oidy direct evidence, 
as set forth with his usual fairness by Mr. Darwin himself, is 
opposed to his views. Several entomologists assured him 
that, in moths, the females evince not the least choice of their 
