On concluding his chapter on choice in pairing among quadrupeds, Mr. Darwin remarks:
It is improbable that the unions of quadrupeds in a state of nature should be left to mere chance. It is much more probable that the females are allured or excited by particular males, who possess certain characters in a higher degree than other males.[14]
As the female among birds selects her partner, he thinks it would be a strange anomaly if among quadrupeds, which stand higher in the scale and have higher mental powers, she did not also exert a choice.[15]
Because of the indifference of the female to the attentions of the male, in order to carry on the processes of reproduction, it was necessary among the lower orders that the male become eager in his pursuit of her, and as a result of this eagerness excessive passion was developed in him. As the most eager would be the most successful in propagating, they would leave the greatest number of offspring to inherit their characters—namely, in males, passion and pugnacity correlated with the physical qualities acquired through Sexual Selection.
On the subject of the acquirement of secondary sexual characters, Mr. Darwin says: “The great eagerness of the males has thus indirectly led to their much more frequently developing secondary sexual characters.” Indeed, by all naturalists, the fact is recognized that the appearance of these characters is closely connected with the reproductive function.
Later experiments have confirmed the observations of Mr. Darwin concerning the intelligence of the female among the lower orders of life. Among these experiments are those recently made by Professor Harper, of the Department of Biology, in the Northwestern University. Professor Harper announces that in all the experiments conducted by him, the female animal showed a greater degree of perception, or intelligence, than the male. He says: “In all my experiments, I found that the female displayed a remarkable quickness in grasping ideas which the male after numerous sluggish efforts finally accomplished.” Professor Harper declared that these facts regarding animals apply with equal force to human beings.
Regarding the power of the female to appreciate the beauty of the males, Mr. Darwin says:
No doubt this implies powers of discrimination and taste on the part of the female which will at first appear extremely improbable; but by the facts to be adduced hereafter, I hope to be able to show that the females actually have these powers.[16]
In commenting on the fact that the female Argus pheasant appreciates the exquisite shading of the ball-and-socket ornaments, and the elegant patterns on the wing-feathers of the male, Mr. Darwin writes:
He who thinks that the male was created as he now exists, must admit that the great plumes which prevent the wings from being used for flight, and which are displayed at courtship and at no other time, in a manner quite peculiar to this species, were given to him as ornaments. If so he must likewise admit that the female was created and endowed with the capacity for appreciating such ornaments. Every one who admits the principle of evolution, and yet feels great difficulty in believing the high taste implied by the beauty of the males, and which generally coincides with our own standard, should reflect that the nerve cells of the brain in the highest as in the lowest members of the vertebrate series are derived from those of the common progenitor of this great kingdom.