IN looking over the life of Wallace recently, my attention was again drawn to the differences in opinion existing between Darwin and himself, with reference to sexual selection. Wallace objected to Darwin's assumption that a bright or peculiar color or a peculiar note or call would attract the attention of other individuals of the same species but of the opposite sex, on the ground that such a process could not become operative in forms which did not have sufficient intelligence to discriminate, and hence could not explain the occurrence of such characters in the lower forms. And if the plaint of the eugenists be accepted at its face value, the degree of intelligence even in the human subject to-day is not sufficient to insure discrimination in choosing a mate.
The development of our knowledge of animal behavior, on the one hand, and the advances in our knowledge of the nervous system, on the other, appear to me to make possible a reconsideration of the matter from the point of view of one or the other of these two lines of work at the present time. It must not be supposed that the approach from this angle will settle the question quite independently of other considerations, but such a method of approach may adduce some independent probability of the soundness or unsoundness of Darwin's point of view.
In the first place, sexual selection with reference to color of coat or plumage or of song is dependent upon the existence of a particular group of sense organs capable of perceiving objects at a distance—the distance receptors as Sherrington calls them. These are the eye and the ear and the olfactory organ. The perception of color and voice depends therefore upon the development of the eye and the ear. Sexual selection with reference to these two characters can not be operative, therefore, in forms not able to see or hear.
It is evident that any other process of selection that is dependent upon coloration, even including protective coloration under certain conditions, must be considered from the same point of view. We may, therefore, discuss the subjects of colors of flowers as a means of attracting bees, warning coloration, protection by mimicry, and certain phases
- Sherrington, "Integrative Action of the Nervous System," New York, 1906.