Secondary Sexual Characters
( Originally Published 1923 )
6. Secondary Sexual Characters.—Among animals in which the behavior of the two sexes is different, even though the eggs are still fertilized in the water, there is in some respect a better adaptation to life. The female salmon, with her tail, scoops away a little sand or gravel in the bottom of a quiet shallow spot, and deposits her eggs in it; the male comes along and de-posits his milt directly on the eggs. There is some-thing here which at once distinguishes the two sexes. There are often external differences between the sexes of various fish species, but here it is a question of bedhavior or instinct. The female deposits eggs only in protected shallows ; the male deposits milt only over the eggs. Now, whatever it is in the blood of the animal, or in the connections of the nervous system, or else-where, that makes the male of the species behave differently from the female is a "secondary fact of sex.
That is, while the difference results somehow from the fact that one individual is a male and another a female, it is not directly connected with the bearing of gametes.
In such animals as frogs and newts we see a further differentiation. Among the former, the male develops a strong voice, resonating pouches connected with the mouth, and peculiar pads on the front feet or hands. These are all related to breeding. The croaking is a courtship performance in the sense that it somehow stimulates the females, who now allow themselves to be grasped by the males. The pads on the hands serve to clasp the female as the male sits on her back. The eggs, as stated above, are discharged directly into the water, and the spermatic fluid directly onto the eggs as they emerge from the body of the female. The voice, the resonating pouches, and the pads are examples of secondary sexual characters, as well as the behavior of the males and females during the breeding period.
As we go up to higher forms of animals, we find a greater variety of structures that are related to courtship, copulation, and care of young, as well as a more complex type of behavior. But differences between the male and the female are not constant features of every species. Indeed, among many birds and even some mammals it is impossible to distinguish the two sexes except by the genitals. The differences which we do find, how-ever, are often so striking that they not only arouse the wonder and curiosity of children, but stimulate the scientific and philosophic speculation of thoughtful adults.
What is the meaning of the lion's mane, the peacock's tail, the nightingale's song, the glowworm's light, the stag's horns, the walrus' tusk? What is the meaning of the changing voice of our own boys during adolescence, of the bearded face, of the combativeness of the male, of the coyness and rounded outlines of the female? These are all examples of secondary sexual characters.
Many of the characteristics which distinguish the male from the female in various species are simply the greater development of some structure or trait in one sex than in the other. The cock's comb is the same as the hen's comb, only more elaborate. The horns of the stag-beetle are the same as the mandibles of the female, exaggerated in their development. The mammary glands of mammals are specialized skin glands, present in both sexes but functional as milk-producers only in the female. If we always found such sex differences, and if they were always cases of greater or less, it would be easier to formulate a theory to account for their development. But the facts being what they are, the secondary sexual character cannot be interpreted as being always related to some advantage for the individual or the species, or as being always the result of inherent differences between "maleness" and "femaleness," although this is at present the best general explanation that can be offered.
If we consider that the gametes themselves differ in a very profound way—as in size, composition, activities -we can readily suppose that in the course of their development they must influence the soma in which they reside and by which they are nourished. Given germ plasm that is male and germ plasm that is female, with fundamental differences between them, it is quite as easy to think that the germ plasm in the embryo determines the maleness or the femaleness of the body, as it is to think of the male body producing male gametes and the female bodies female gametes. Moreover, it is more in accord with what we know of the development of the embryo to consider the presence of male germ plasm to be the "cause" of the formation of a male carrier, and to consider the presence of female germ plasm as the "cause" of the formation of a female carrier.
If we compare the characteristics of the two kinds of germ cells with the characteristics of what we commonly consider male and female personalities, whether in human beings or in other organisms, this thought will be clearer. Associated with differences in size of gametes are the facts of the generally greater size of female bodies in many species, of the greater ease of assimilating food, and of the capacity to store away reserves of food. This relation to food may be further connected with the fact that it is the female that supplies food to the eggs where the eggs are discharged from the body; and among those species that develop the young internally, it is the female which nourishes the embryo, and even the young. The male, on the other hand, is the more active, not only as gamete, but as soma or body. This means a greater capacity to use up food, to liberate energy. This shows itself further in the generally greater elaboration of pigments, horns, hairs, feathers, and so on—all indications of a more intense activity on the part of the protoplasm, of the more rapid destruction of protoplasm.
Again, the greater motility of the male gamete may be related to the greater impulsiveness and aggressiveness of the male individual, as compared to the sluggishness of the female gamete and the greater passivity of the female individual. We are familiar on the one side with the capacity for great outbursts of energy; on the other, with the capacity for great endurance. The venturesomeness of the male may be contrasted with the conservatism of the female. These contrasts are of course not to be considered in any absolute sense; and we must not infer from them too much by way of establishing standards of what boys and girls, men and women, ought or ought not to do and be. Yet they are suggestive of fundamental differences which are worth considering in our efforts to understand the place of sex in life.
There can be no question that the boy begins to show male characteristics and the girl to show female characteristics from the day of birth. We should learn to recognize and to value these differentiated manifestations of fundamental human traits, and eventually to guide them into the most profitable modes of expression, just as we consider it important to guide the various impulses which supply the energy for all activities.
Since we must consider that all impulses are of potential service, regardless of how they first show themselves, and regardless of how easily they are turned into undesirable or even disastrous types of activity, so must we consider that the traits which distinguish males and females have potential values, instead of assuming that some traits are better than others, or that some are even undesirable. It is more profitable again to take the children as we find them and see what can be done with them, rather than to set up a more or less arbitrary model of what we think children ought to be and attempt to coerce the developing organism into conformity with our standard.
The secondary sexual characters, beginning with mere accessories of the gonads, such as ducts and various glands (for example, yolk glands and shell glands among birds), and leading up to structures and activities only remotely connected with the gonads (such as milk glands and nest-building), may be looked upon as by-products of the exuberance of the germ plasm. They are the surplus, the overflow from the life abundant. Where life is found in its lowest terms, among the simplest plants and animals, there is food-getting, escape from enemies, direct reproduction. There is, so to say, no margin for display, no reserve for extras. Among the highest plants and animals, those that have developed adequate apparatus for insuring the essentials of material existence, the surplus is turned into elaborations of structures and processes related to reproduction. This does not imply, of course, that these plants and animals are in any sense conscious of a desire to display, to venture, to experiment. It is intended only to suggest that the activity of living matter, protoplasm, will continue in proportion as there is an abundance of the necessities. Overfeeding does indeed often interfere with reproduction; but starved organisms never produce either abundant offspring or brilliant secondary structures.
Among human beings, also, abundant supplies of emotional energy are necessary to produce the activities which are most suggestive of the secondary sexual processes found in other animals. Considered from this point of view, we may perhaps more easily find ways of utilizing these manifestations. The preening of birds is suggested by the display and coquetry of our adolescents ; song in the bird, like bellowing in the elephant or the bull, suggests outbursts of strong feeling, just as it does in human beings. The dance has its homolog among insects, crabs, spiders, and many backboned animals. The increased sensitiveness to color, odor, taste, as well as to touch, with the advance of puberty, is paralleled by similar phenomena during the breeding period of many animals. Finally, these conditions fail altogether, both among human beings and among other animals, if the primary sex organs, that is the gonads, are removed or injured early in life. That is to say, the capacity to develop these secondary characters depends upon the presence of the germinal tissues in the body. And among human beings these secondary characters are the foundation of all the art and music, poetry, and dance, and other qualities that we consider the most distinctly human traits in our whole constitution.
There is much in our past traditions that stands in the way of a ready acceptance of this view of the relation between the highest manifestations of humanity and the roots of our character in sexual organs and processes. Yet the very philosophy which has condemned sex to the dark corners of shame gives evidence of very keen insight or of a sound instinct; for it discredits equally dancing and music, painting and sculpture, humor and drama, adventure and research. The quest for beauty and light and laughter is denounced because, like sensual debauchery, it is a search for pleasure. But we can save ourselves a great deal of unnecessary worry if we recognize that we are dealing with a primitive force which, like fire or electricity, can either be turned to the highest service or be allowed to become a source of dire calamity. It is not the force of the sexual impulse which is either good or bad but the use to which we put it.