The Courtship of Animals

by W. P. Pycraft

Nature is nothing, if not perverse. And hence it happens that there are many exceptions to every rule which one formulates. Among the birds, for example, there are species wherein the rule that the female follows her mate in the acquisition of new characters is, so to speak, set aside. She follows a line of her own. This is true, at any rate, of superficial characters, such as coloration. By some curious change in her “metabolism,” as the conversion into living tissue of the substances taken as food is called, this coloration may attain a brilliance in no way inferior to that of the male, but strikingly different. The beautiful Orange Fruit-pigeon (Chrysoenas victor) furnishes a case in point, the male being of a gorgeous orange-yellow, the female of a no less vivid green. But the differences are not so great as they appear at first sight. For the male was originally green, and the female has thus but intensified the ancestral livery. Green, it should be remarked, of a more or less olive shade, always precedes yellow in development; and yellow may yield to red, but this order is never reversed. A no less striking case is that of the Upland Goose (Cloephaga magellanica), the male of which is pure white, while the female wears a livery of chestnut and brown. But so sharply are the colours defined that it would be difficult to say that one was of a higher order of coloration than the other. To what causes or factors are these departures due?

Reproduction in the simplest living things takes place by a simple division of the body into two as soon as its maximum size or adult condition has been attained. In such simple types the body consists only of a single “blob,” or particle, of jelly. But a new era began when large numbers of such particles, or “cells,” began to form coherent masses, different parts of the mass performing different work for the mutual benefit of the community. Some have come to form what we call the body, which is born, and in due course dies. Others are alone concerned with the task of reproduction. They are nourished by the body, and on attaining maturity, give rise to new bodies. These reproductive cells are excessively small. The male, or “sperm” cell, can only be distinguished under the highest powers of the microscope. The female cell, or “Ovum,” is always larger than the male, because, in addition to the germinal matter which it contains, it is furnished with a store of food in the shape of yolk. This accounts for the relatively enormous size of the egg of the hen. Within the hardened shell the germ develops into the chick, deriving food for its growth from this generous store. Where this yolk is limited in quantity the growing body is hastily fashioned, and launched forth into the world in the form of a “larva,” when it must forage for itself till it has attained its adult form. Or it is retained within the body of the mother until development is complete.

The reproductive cells are the bearers of the Germ-plasm, the stuff of which man and the beasts of the field alike are fashioned. Only a portion of this germ-plasm gives rise to a new body; the rest is, as it were, held over and stored within the new body to give rise to another in due course. That which produces the body we call the “Somatoplasm,” because it is the “plasm” or stuff of which the “Soma,” or body, is made. As to the nature of this Germ-plasm and its mysterious properties, a wide divergency of opinion exists among savants. But the views which find most favour to-day are those of the veteran Professor August Weissmann, as set forth in his work on the “Germ-Plasm, a Theory of Heredity.”

The excessively minute quantity of this germ-plasm which suffices to form a new body is incredible. By what miracle of miracles is the essence of a man distilled? His body arises from the union or commingling of two particles of living matter so minute as to be invisible to the naked eye. One of these particles is the “sperm”—cell furnished by the male parent; the other, the “ovum,” furnished by the mother. True the ovum may measure as much as the one-hundred and fiftieth part of an inch, but the bulk of this is yolk-food necessary to furnish the tender germ with life and energy till it shall have attached itself to the walls of the womb, whence all its future nourishment is derived.

By no process of analysis known to us could the germ-plasm of man be distinguished from that of, say, a jelly-fish; and in the matter of quantity there is no more difference. Yet, identical to our senses, in potentiality how amazingly different are these two particles of jelly! In the lowliest animals, such as jelly-fish, one cannot distinguish male and female at sight. The appearance of separate male and female individuals begins somewhat high in the scale marking an epoch in the history of animal life. For the birth of sex inaugurated not merely individuals producing distinctive “male” and “female” germs, but individuals which, by virtue of their sex, developed differences of behaviour and mentality which were to be followed by tremendous consequences. Certain aspects of this behaviour are to furnish the theme of these pages; others, and no less important, those who will may discover in Professor Arthur Thomson’s “Evolution of Sex.”

We are far, indeed, from being able to explain the attributes of sex. At most, we can but endeavour to interpret the behaviour associated therewith. This was the task which Darwin set himself to achieve in his theory of sexual selection. He was influenced in the train of thought which he followed up with such brilliant success by what he had observed in the behaviour of highly-ornamented species, such as the Peacock and the Birds of Paradise. The strange antics of these birds when under the influence of sexual excitement persuaded him that they were at least dimly conscious of their splendour, and of its power to fascinate. The female, on the other hand, was supposed to be coy, and to bestow her person on the finest performer. In this way the dullest birds and the poorest performers were gradually eliminated. Here, indeed, was sexual selection. The frills thus begotten he called “Secondary Sexual Characters,” a term which is also used, and was used, by him, to include any feature whereby the sexes can be distinguished apart from the character of the genital organs.

Horns, tusks, and spurs are other forms of secondary sexual characters. And these stand for another form of sexual selection—that of selection by battle. Herein victory falls to the strongest and most pugnacious male who, as the spoils of victory, annexes the females which formed the subject of the duel. This theory, which must be discussed at greater length in the course of these pages, has had many critics, and among them men of mark. But whatever modifications may be deemed necessary, they will be such as are demanded by the results of later discoveries rather than to the force and subtlety of the arguments of his opponents.

One of the most formidable of the opponents of the Sexual Selection theory was Wallace. But his arguments were far from convincing, and often inconsistent. He attributed the more frequent occurrence in male animals of brilliant coloration and exaggerations of growth such as give rise to manes, beards, long plumes, and so on, to a “surplus of strength, vitality and growth-power which is able to expend itself in this way without injury,” or, as he sometimes expresses it, to superabundant vitality. He was evidently striving to find words for the faith that was in him, and he was nearer the truth than he knew or than his critics supposed. He was seeking facts which only the physiologist could furnish. And these made their appearance long years after with Professor Starling’s discovery of Hormones. We are far from understanding the origin of these mysterious juices which must be so frequently alluded to in these pages, but they are evidently intimately associated with the expenditure of energy. This may sometimes find an outlet in increased stature, sometimes in pure luxuries of growth. The force of Wallace’s arguments was crushed out by the weight of detail they were made to bear.

Mr. J. T. Cunningham a few years ago entered the lists and failed to achieve his purpose no less completely. His was a theory which assumed too much. In the first place it was based on the transmissibility of acquired characters, of the truth of which there is at present no evidence.

He contends, for example, that the vivid hues of scarlet, blue, yellow and violet which colour the naked skin of the neck of the cassowaries and of both sexes, and the curious horny casque which surmounts the head, are the outcome of the constant laceration of the skin inflicted by the males during their conflicts for the possession of the females. He assumes that such conflicts take place, and he assumes that such “acquired characters” are transmitted. Now, as a matter of fact, these birds do not fight with their beaks, but with their feet. And to this end the claw of the inner toe is enlarged to form a great spur. But there is no evidence that the skin of the neck is ever damaged in such conflicts as they may engage in. No scars are ever found, at any rate, to lend support to this theory. The casque, which is similarly supposed to be a mark of honourable conflict, is an “ornament” of great frailty, for it is composed of a delicate filigree-work of bone covered with a thin sheath of horn. In like manner, the long plumes which surmount the heads of birds like the Peacock, and many Birds of Paradise, and the wattle which surmounts the beak of the Turkey, are supposed to have had their origin in similar pugilistic encounters in the past. Mr. Cunningham is surely pushing the theory of the transmission of acquired characters a little far. For what has been transmitted in these cases is not a number of scarred surfaces, but a series of hypertrophied structures. An amazing array of ornamental characters, symmetrically disposed, and often vividly coloured, in short, has been produced from lacerated tissues which in kind and extent can have varied but little.