The Courtship of Animals

by W. P. Pycraft

Evidence has been accumulating during the last few years which would have rejoiced the heart of Darwin. Had he known that birds of sober hues “display” with the same animation and with as much elaboration of posture as the Peacock and the Pheasant, his theory of “Sexual Selection “would probably have left little for those who came after him to criticize. Since his time it has been discovered that both permanent and recurrent secondary sexual characters, such as the antlers of deer and the temporary nuptial plumage of birds, such as the Ruff for example, are controlled as to their growth by the stimulating action of the “secretions or juices formed by certain of the ductless glands “; that is to say, of glands having no apparent connection with their surrounding tissues. We owe much of our knowledge of this subject to Professor Starling, who has called these secretions “Hormones.”

Darwin knew that the essential sexual glands, the testes and the ovaries, in some mysterious way controlled, in a large degree, the development of these “hall-marks” of sex, for it was known in his time that castrated stags failed to produce antlers, and that hen pheasants, for example, in extreme old age, or when the ovaries were damaged by disease or injury, at once assumed the plumage of the cock; but the part played by these ductless glands was quite unsuspected. They are the Thyroid, and the Thymus glands, which are attached to the outer walls of the trachea or windpipe. The Pituitary body, which forms part of the brain, and the Suprarenal bodies, attached to the kidneys. It would be foreign to the purpose of these pages to enter into the functions of these glands; suffice it to say, that the juices formed therein are taken up by the blood, and distributed over the system. Their action is only very imperfectly understood. We know that any derangement in their efficiency results in disease, and that they play a very important part in the reproductive system, as will become abundantly evident in the course of these pages. Much hitherto attributed to the action of “Sexual Selection” alone, it is now evident is largely due to their action.

The all-sufficiency of the “Sexual Selection” theory to account for the development of armature, such as horns, antlers, and the huge spine-like outgrowths which form so conspicuous a feature of many of the extinct Land-dragons, or Dinosaurs, has been by no means universally accepted. Some authorities like Dr. A. Smith Woodward and Professor Osborne interpret these after another fashion. They hold that these are the “expression points” of inherent growth forces, a process of concentration marking the final stages of evolution prior to extinction. From which it may be inferred that there is a term to the life of a species as there is to the life of the individual. In many cases it is suggested the very exuberance of growth has been the exterminating factor, as in the case of the huge antlers of the Irish “elk,” whose enormous weapons hampered his endeavours to escape his enemies. This is the theory of “Orthogenesis,” or direct development. According to this, new structures, arising in the germ-plasm as “variations,” will of their own inherent vitality go on increasing in each generation unless, and until, checked by “Natural Selection.” Changes in the character of the “Hormones” might very well bring about these excesses of growth. It is well known that the exuberance of growth which produces giants among the human race is due to a derangement of the secretions or hormones of the pituitary body which largely control growth.

Another factor of Sexual Selection which is commonly ignored, but which is of profound importance, is to be found in the part played by the emotions in regard to sexual relationships; the part which the “mind” has played, and plays, in the mating of animals, at any rate of the higher types.

Darwin touched but lightly on this theme. Later writers have almost entirely ignored it. Almost all that is worth knowing on the subject we owe to Professor Lloyd Morgan, who was one of the first to take up this difficult line of investigation, and to Professor Groos. Their researches have shown that there can be no doubt but that the emotions have played and are playing an important part in the phenomena we are striving to analyse. Sexual selection, in short, is concerned not merely with the evolution of the physical characters of the body, but also, and no less, with the psychological attributes thereof. Many new and extremely valuable facts in this regard have been brought to light by Mr. H. Eliot Howard in the course of his remarkable studies on our native warblers. Not until the psychology of sex in the lower orders of creation has been further investigated shall we have a properly balanced account of the part played by sexual selection in the scheme of evolution.

By now it will have become apparent that the study of the “Courtship” of animals is one of alluring interest and full of pitfalls for the unwary. And this because of the apparent difficulty in drawing any hard-and-fast line between the part played by “Natural” and the part played by “Sexual” Selection, at any rate in some cases.

To this aspect of the theme Professor Lloyd Morgan has drawn particular attention. “It is difficult,” he remarks, to accept the view that individual choice has played no part where the sexual instincts are concerned. But supposing that it has played its part ... the effects will be wrought into the congenital tissue of the race if, and only if, there are certain individuals which, through failure to elicit the pairing response, die unmated. Is preferential mating, supposing it to occur, carried to such a degree that some individuals fail to secure a mate? That is the question. If so, sexual selection is a factor in race progress; if not, though it may occur in nature, it is inoperative as a means of evolutionary development. The whole question, in itself a difficult one, is further complicated by the fact that the males which are possessed of the most exuberant vitality, and are therefore by hypothesis rendered the most acceptable through emotional suggestion, are likely to compete with other males of less exuberant vitality by direct combat. Such competition, by which the weakest are excluded from mating through no choice on the part of the female, falls under the head of natural selection, and not of sexual selection, if by that term we understand preferential mating.

“This serves to bring out the difference ... between natural selection through elimination and conscious selection through choice.... Sexual selection by preferential mating begins by selecting the most successful in stimulating the pairing instinct.... The process is determined by conscious choice. It is in and through such choice that consciousness has been a factor in evolution.”

Herein Lloyd Morgan, like Darwin, recognizes the existence of a dual machinery in determining survival, where this depends on the co-operation of two individuals leading separate existences—Natural, and Sexual, Selection—sometimes the one and sometimes the other prevailing. In the former, the females are seized by force; in the latter, won by displays.

But is this really so? In these pages it is contended that a sharp line must be drawn between all those attributes and characters which are necessary to achieve individual survival, the survival of the Ego, and all those which, on the other hand, are necessary to achieve reproduction and the survival of the race. The former are governed, or determined, by Natural, the latter by Sexual, Selection.