Sexual Selection

Abstract

MR. DARWIN in his recent work on the “Descent of Man has shown that throughout the animal kingdom the male generally displays the stronger passions and is always the most eager. The males, moreover, whenever secondary sexual characters occur, are, as a rule, the possessors of weapons for defence or offence, brilliant colours, or other ornamental appendages, all of which Mr. Darwin supposes to have been acquired through sexual selection, either for the purpose of charming the female or for struggling with other males for the possession of the females. In a few exceptional cases among birds, the females are the wooers, and these are then more brilliantly coloured than the males. In Westwood's work on insects^* I met with the following passage:—“M. Donzel has published a curious memoir upon the flight of butterflies whilst coupling (Ann. Soc. Ent. de France, 1837, P. 77.) showing that whilst the males of Pontia Brassicæ, &c., Colias, and Polyommatus support the females, it is the latter which support their partners in the genera Thais, Thecla, Argynnis, Melitæa, Hipparchia, and Pieris.” Now this is strictly analogous to these exceptional birds, because, among our British representatives of these genera whenever a considerable sexual difference of colour occurs, the female is always the more brilliantly coloured. Thus, the female Thecla Quercus has the bright purple patch, and the female Thecla Betulæ the brilliant orange blotch on the fore wing, while the females of Hipparchia (Satyrus), Janira, and H. Semele are considerably brighter than their partners. The female H. Megæra is rather brighter than the male, and the same is true of Colias Edusa and C. Hyale, since the females of these species have orange or yellow spots in the black marginal border, represented in the males by thin streaks only. The females of the whole genus Pieris also are ornamented with black spots on the fore wings, which are only partially present in the males. I must confess that I am not convinced of the action of sexual selection in producing the colours of insects, but it cannot be denied that these facts are strikingly corroborative of Mr. Darwin's views. With few exceptions the rule holds good throughout the exotic species of these genera.