"powers of discrimination and taste on the part of the female" (p. 211[21]); "the females habitually or occasionally prefer the more beautiful males," "there is little improbability in the females of insects appreciating beauty in form or color" (p. 329); he speaks of birds as the most "esthetic" of all animals excepting man, and adds that they have "nearly the same taste for the beautiful as we have" (p. 359); he remarks that a change of any kind in the structure or color of the male bird "appears to have been admired by the female" (p. 385). He speaks of the female Argus pheasant as possessing "this almost human degree of taste." Birds, again, "seem to have some taste for the beautiful both in color and sound," and "we ought not to feel too sure that the female does not attend to each detail of beauty" (p. 421). Novelty, he says, is "admired by birds for its own sake" (p. 495). "Birds have fine powers of discrimination and in some few instances it can be shown that they have a taste for the beautiful" (p. 496). The "esthetic capacity" of female animals has been advanced by exercise just as our own taste has improved (p. 616). On the other hand, we find running throughout the book quite another idea. Of cicadas he tells us that it is probable that, "like female birds, they are excited or allured by the male with the most attractive voice" (p. 282); and, coming to _Locustidæ_, he states that "all observers agree that the sounds serve either to call or excite the mute females" (p. 283). Of birds he says, "I am led to believe that the females prefer or are most excited by the more brilliant males" (p. 316). Among birds also the males "endeavor to charm or excite their mates by love-notes," etc., and "the females are excited by certain males, and thus unconsciously prefer them" (p. 367), while ornaments of all kinds "apparently serve to excite, attract, or fascinate the female" (p. 394). In a supplemental note, also, written in 1876, five years after the first publication of the _Descent of Man_, and therefore a late statement of his views, Darwin remarks that "no supporter of the principle of sexual selection believes that the females select particular points of beauty in the males; they are merely excited or attracted in a greater degree by one male than by another, and this seems often to depend, especially with birds, on brilliant coloring" (p. 623). Thus, on the one hand, Darwin interprets the phenomena as involving a real esthetic element, a taste for the beautiful; on the other hand, he states, without apparently any clear perception that the two views are quite distinct, that the colors and sounds and other characteristics of the male are not an appeal to any esthetic sense of the female, but an appeal to her sexual emotions, a stimulus to sexual excitement, an allurement to sexual contact. According to the first theory, the female admires beauty, consciously or unconsciously, and selects the most beautiful partner[22]; according to the second theory, there is no esthetic question involved, but the female is unconsciously influenced by the most powerful or complex organic stimulus to which she is subjected. There can be no question that it is the second, and not the first, of these two views which we are justified in accepting. Darwin, it must be remembered, was not a psychologist, and he lived before the methods of comparative psychology had begun to be developed; had he written twenty years later we may be sure he would never have used so incautiously some of the vague and hazardous expressions I have quoted. He certainly injured his theory of sexual selection by stating it in too anthropomorphic language, by insisting on "choice," "preference," "esthetic sense," etc. There is no need whatever to burden any statement of the actual facts by such terms borrowed from human psychology. The female responds to the stimulation of the male at the right moment just as the tree responds to the stimulation of the warmest days in spring. We should but obscure this fact by stating that the tree "chooses" the most beautiful days on which to put forth its young sprouts. In explaining the correlation between responsive females and accomplished males the supposition of esthetic choice is equally unnecessary. It is, however, interesting to observe that, though Darwin failed to see that the love-combats, pursuits, dances, and parades of the males served as a method of stimulating the impulse of contrectation--or, as it would be better to term it, tumescence--in the male himself,[23] he to some extent realized the part thus played in exciting the equally necessary activity of tumescence in the female.
The justification for using the term "tumescence," which I here propose, is to be found in the fact that vascular congestion, more especially of the parts related to generation, is an essential preliminary to acute sexual desire. This is clearly brought out in Heape's careful study of the "sexual season" in mammals. Heape distinguishes between the "pro-estrum," or preliminary period of congestion, in female animals and the immediately following "estrus," or period of desire. The latter period is the result of the former, and, among the lower animals at all events, intercourse only takes place during the estrus, not during the pro-estrum. Tumescence must thus be obtained before desire can become acute, and courtship runs _pari passu_ with physiological processes. "Normal estrus," Heape states, "occurs in conjunction with certain changes in the uterine tissue, and this is accompanied by congestion and stimulation or irritation of the copulatory organs...Congestion is invariably present and is an essential condition...The first sign of pro-estrum noticed in the lower mammals is a swollen and congested vulva and a general restlessness, excitement, or uneasiness. There are other signs familiar to breeders of various mammals, such as the congested conjunctiva of the rabbit's eye and the drooping ears of the pig. Many monkeys exhibit congestion of the face and nipples, as well as of the buttocks, thighs, and neighboring parts; sometimes they are congested to a very marked extent, and in some species a swelling, occasionally prodigious, of the soft tissues round the anal and generative openings, which is also at the time brilliantly congested, indicates the progress of the pro-estrum...The growth of the stroma-tissue [in the uterus of monkeys during the pro-estrum] is rapidly followed by an increase in the number and size of the vessels of the stroma; the whole becomes richly supplied with blood, and the surface is flushed and highly vascular. This process goes on until the whole of the internal stroma becomes tense and brilliantly injected with blood...In all essential points the menstruation or pro-estrum of the human female is identical with that of monkeys...Estrus is possible only after the changes due to pro-estrum have taken place in the uterus. A wave of disturbance, at first evident in the external generative organs, extends to the uterus, and after the various phases of pro-estrum have been gone through in that organ, and the excitement there is subsiding, it would seem as if the external organs gain renewed stimulus, and it is then that estrus takes place...In all animals which have been investigated coition is not allowed by the female until some time after the swelling and congestion of the vulva and surrounding tissue are first demonstrated, and in those animals which suffer from a considerable discharge of blood the main portion of that discharge, if not the whole of it, will be evacuated before sexual intercourse is allowed." (W. Heape, "The 'Sexual Season' of Mammals," _Quarterly Journal of Microscopical Science_, vol. xliv, Part I, 1900. Estrus has since been fully discussed in Marshall's _Physiology of Reproduction_.) This description clearly brings out the fundamentally vascular character of the process I have termed "tumescence"; it must be added, however, that in man the nervous elements in the process tend to become more conspicuous, and more or less obliterate these primitive limitations of sexual desire. (See "Sexual Periodicity" in the first volume of these _Studies_.)
Moll subsequently restated his position with reference to my somewhat different analysis of the sexual impulse, still maintaining his original view ("Analyse des Geschlechtstriebes," _Medizinische Klinik_, Nos. 12 and 13, 1905; also _Geschlecht und Gesellschaft_, vol. ii, Nos. 9 and 10). Numa Praetorius (_Jahrbuch für Sexeuelle Zwischenstufen_, 1904, p. 592) accepts contrectation, tumescence, and detumescence as all being stages in the same process, contrectation, which he defines as the sexual craving for a definite individual, coming first. Robert Müller (_Sexualbiologie_, 1907, p. 37) criticises Moll much in the same sense as I have done and considers that contrectation and detumescence cannot be separated, but are two expressions of the same impulse; so also Max Katte, "Die Präliminarien des Geschlechtsaktes," _Zeitschrift für Sexualwissenschaft_, Oct., 1908, and G. Saint-Paul, _L'Homosexualité et les Types Homosexuels_, 1910, p. 390.
While I regard Moll's analysis as a valuable contribution to the elucidation of the sexual impulse, I must repeat that I cannot regard it as final or completely adequate. As I understand the process, contrectation is an incident in the development of tumescence, an extremely important incident indeed, but not an absolutely fundamental and primitive part of it. It is equally an incident, highly important though not primitive and fundamental, of detumescence. Contrectation, from first to last; furnishes the best conditions for the exercise of the sexual process, but it is not an absolutely essential part of the process and in the early stages of zoölogical development it had no existence at all. Tumescence and detumescence are alike fundamental, primitive, and essential; in resting the sexual impulse on these necessarily connected processes we are basing ourselves on the solid bedrock of nature.
Moreover, of the two processes, tumescence, which in time comes first, is by far the most important, and nearly the whole of sexual psychology is rooted in it. To assert, with Moll, that the sexual process may be analyzed into contrectation and detumescence alone is to omit the most essential part of the process. It is much the same as to analyze the mechanism of a gun into probable contact with the hand, and a more or less independent discharge, omitting all reference to the loading of the gun. The essential elements are the loading and the discharging. Contrectation is a part of loading, though not a necessary part, since the loading may be effected mechanically. But to understand the process of firing a gun and to comprehend the mechanism of the discharge, we must insist on the act of loading and not merely on the contact of the hand. So it is in analyzing the sexual impulse. Contrectation is indeed highly important, but it is important only in so far as it aids tumescence, and so may be subordinated to tumescence, exactly as it may also be subordinated to detumescence. It is tumescence which is the really essential part of the process, and we cannot afford, with Moll, to ignore it altogether.
Wallace opposed Darwin's theory of sexual selection, but it can scarcely be said that his attitude toward it bears critical examination. On the one hand, as has already been noted, he saw but one side of that theory and that the unessential side, and, on the other hand, his own view really coincided with the more essential elements in Darwin's theory. In his _Tropical Nature_ he admitted that the male's "persistency and energy win the day," and also that this "vigor and liveliness" of the male are usually associated with intense coloration, while twenty years later (in his _Darwinism_) he admitted also that it is highly probable that the female is pleased or excited by the male's display. But all that is really essential in Darwin's theory is involved, directly or indirectly, in these admissions.
Espinas, in 1878, in his suggestive book, _Des Sociétés Animales_, described the odors, colors and forms, sounds, games, parades, and mock battles of animals, approaching the subject in a somewhat more psychological spirit than either Darwin or Wallace, and he somewhat more clearly apprehended the object of these phenomena in producing mutual excitement and stimulating tumescence. He noted the significance of the action of the hermaphroditic snails in inserting their darts into each other's flesh near the vulva in order to cause preliminary excitation. He remarks of this whole group of phenomena: "It is the preliminary of sexual union, it constitutes the first act of it. By it the image of the male is graven on the consciousness of the female, and in a manner impregnates it, so as to determine there, as the effects of this representation descend to the depths of the organism, the physiological modifications necessary to fecundation." Beaunis, again, in an analysis of the sexual sensations, was inclined to think that the dances and parades of the male are solely intended to excite the female, not perceiving, however, that they at the same time serve to further excite the male also.[24] A better and more comprehensive statement was reached by Tillier, who, to some extent, may be said to have anticipated Groos. Darwin, Tillier pointed out, had not sufficiently taken into account the coexistence of combat and courtship, nor the order of the phenomena. Courtship without combat, Tillier argued, is rare; "there is a normal coexistence of combat and courtship."[25] Moreover, he proceeded, force is the chief factor in determining the possession of the female by the male, who in some species is even prepared to exert force on her; so that the female has little opportunity of sexual selection, though she is always present at these combats. He then emphasized the significant fact that courtship takes place long after pairing has ceased, and the question of selection thus been eliminated. The object of courtship, he concluded, is not sexual selection by the female, but the sexual excitement of both male and female, such excitement, he asserted, not only rendering coupling easier, but favoring fecundation. Modesty, also, Tillier further argued, again anticipating Groos, works toward the same end; it renders the male more ardent, and by retarding coupling may also increase the secretions of the sexual glands and favor the chances of reproduction.[26] In a charming volume entitled _The Naturalist in La Plata_ (1892) Mr. W.H. Hudson included a remarkable chapter on "Music and Dancing in Nature." In this chapter he described many of the dances, songs, and love-antics of birds, but regarded all such phenomena as merely "periodical fits of gladness." While, however, we may quite well agree with Mr. Hudson that conscious sexual gratification on the part of the female is not the cause of music and dancing performances in birds, nor of the brighter colors and ornaments that distinguish the male, such an opinion by no means excludes the conclusion that these phenomena are primarily sexual and intimately connected with the process of tumescence in both sexes. It is noteworthy that, according to H.E. Howard ("On Sexual Selection in Birds," _Zoölogist_, Nov., 1903), color is most developed just before pairing, rapidly becoming less beautiful--even within a few hours--after this, and the most beautiful male is most successful in getting paired. The fact that, as Mr. Hudson himself points out, it is at the season of love that these manifestations mainly, if not exclusively, appear, and that it is the more brilliant and highly endowed males which play the chief part in them, only serves to confirm such a conclusion. To argue, with Mr. Hudson, that they cannot be sexual because they sometimes occur before the arrival of the females, is much the same as to argue that the antics of a kitten with a feather or a reel have no relationship whatever to mice. The birds that began earliest to practise their accomplishments would probably have most chance of success when the females arrived. Darwin himself said that nothing is commoner than for animals to take pleasure in practising whatever instinct they follow at other times for some real good. These manifestations are primarily for the sake of producing sexual tumescence, and could not well have been developed to the height they have reached unless they were connected closely with propagation. That they may incidentally serve to express "gladness" one need not feel called upon to question.
Another observer of birds, Mr. E. Selous, has made observations which are of interest in this connection. He finds that all bird-dances are not nuptial, but that some birds--the stone-curlew (or great plover), for example--have different kinds of dances. Among these birds he has made the observation, very significant from our present point of view, that the nuptial dances, taken part in by both of the pair, are immediately followed by intercourse. In spring "all such runnings and chasings are, at this time, but a part of the business of pairing, and one divines at once that such attitudes are of a sexual character...Here we have a bird with distinct nuptial (sexual) and social (non-sexual) forms of display or antics, and the former as well as the latter are equally indulged in by both sexes." (E. Selous, _Bird Watching_, pp. 15-20.)
The same author (ibid., pp. 79, 94) argues that in the fights of two males for one female--with violent emotion on one side and interested curiosity on the other--the attitude of the former "might gradually come to be a display made entirely for the female, and of the latter a greater or less degree of pleasurable excitement raised by it, with a choice in accordance." On this view the interest of the female would first have been directed, not to the plumage, but to the frenzied actions and antics of the male. From these antics in undecorated birds would gradually develop the interest in waving plumes and fluttering wings. Such a dance might come to be of a quite formal and non-courting nature.
Last, we owe to Professor Häcker what may fairly be regarded, in all main outlines, as an almost final statement of the matter. In his _Gesang der Vögel_ (1900) he gives a very clear account of the evolution of bird-song, which he regards as the most essential element in all this group of manifestations, furnishing the key also to the dancing and other antics. Originally the song consists only of call-cries and recognition-notes. Under the parallel influence of natural selection and sexual selection they become at the pairing season reflexes of excitement and thus develop into methods of producing excitement, in the male by the muscular energy required, and in the female through the ear; finally they become play, though here also it is probable that use is not excluded. Thus, so far as the male bird is concerned, bird-song possesses a primary prenuptial significance in attracting the female, a secondary nuptial significance in producing excitement (p. 48). He holds also that the less-developed voices of the females aid in attaining the same end (p. 51). Finally, bird-song possesses a tertiary extranuptial significance (including exercise play, expression of gladness). Häcker points out, at the same time, that the maintenance of some degree of sexual excitement beyond pairing time may be of value for the preservation of the species, in case of disturbance during breeding and consequent necessity for commencing breeding over again.
Such a theory as this fairly coincides with the views brought forward in the preceding pages,--views which are believed to be in harmony with the general trend of thought today,--since it emphasizes the importance of tumescence and all that favors tumescence in the sexual process. The so-called esthetic element in sexual selection is only indirectly of importance. The male's beauty is really a symbol of his force.
It will be seen that this attitude toward the facts of tumescence among birds and other animals includes the recognition of dances, songs, etc., as expressions of "gladness." As such they are closely comparable to the art manifestations among human races. Here, as Weismann in his _Gedanken über Musik_ has remarked, we may regard the artistic faculty as a by-product: "This [musical] faculty is, as it were, the mental hand with which we play on our own emotional nature, a hand not shaped for this purpose, not due to the necessity for the enjoyment of music, but owing its origin to entirely different requirements."
The psychological significance of these facts has been carefully studied and admirably developed by Groos in his classic works on the play instinct in animals and in men.[27] Going beyond Wallace, Groos denies _conscious_ sexual selection, but, as he points out, this by no means involves the denial of unconscious selection in the sense that "the female is most easily won by the male who most strongly excites her sexual instincts." Groos further quotes a pregnant generalization of Ziegler: "In all animals a high degree of excitement of the nervous system is _necessary to procreation_, and thus we find an excited prelude to procreation widely spread."[28] Such a stage, indeed, as Groos points out, is usually necessary before any markedly passionate discharge of motor energy, as may be observed in angry dogs and the Homeric heroes. While, however, in other motor explosions the prelude may be reduced to a minimum, in courtship it is found in a highly marked degree. The primary object of courtship, Groos insists, is to produce sexual excitement.
It is true that Groos's main propositions were by no means novel. Thus, as I have pointed out, he was at most points anticipated by Tillier. But Groos developed the argument in so masterly a manner, and with so many wide-ranging illustrations, that he has carried conviction where the mere insight of others had passed unperceived. Since Darwin wrote the _Descent of Man_ the chief step in the development of the theory of sexual selection has been taken by Groos, who has at the same time made it clear that sexual selection is largely a special case of natural selection.[29] The conjunction of the sexes is seen to be an end only to be obtained with much struggle; the difficulty of achieving sexual erethism in both sexes, the difficulty of so stimulating such erethism in the female that her instinctive coyness is overcome, these difficulties the best and most vigorous males,[30] those most adapted in other respects to carry on the race, may most easily overcome. In this connection we may note what Marro has said in another connection, when attempting to answer the question why it is that among savages courtship becomes so often a matter in which persuasion takes the form of force. The explanation, he remarks, is yet very simple. Force is the foundation of virility, and its psychic manifestation is courage. In the struggle for life violence is the first virtue. The modesty of women--in its primordial form consisting in physical resistance, active or passive, to the assaults of the male--aided selection by putting to the test man's most important quality, force. Thus it is that when choosing among rivals for her favors a woman attributes value to violence.[31] Marro thus independently confirms the result reached by Groos.
The debate which has for so many years been proceeding concerning the validity of the theory of sexual selection may now be said to be brought to an end. Those who supported Darwin and those who opposed him were, both alike, in part right and in part wrong, and it is now possible to combine the elements of truth on either side into a coherent whole. This is now beginning to be widely recognized; Lloyd Morgan,[32] for instance, has readjusted his position as regards the "pairing instinct" in the light of Groos's contribution to the subject. "The hypothesis of sexual selection," he concludes, "suggests that the accepted male is the one which adequately evokes the pairing impulse...Courtship may thus be regarded from the physiological point of view as a means of producing the requisite amount of pairing hunger; of stimulating the whole system and facilitating general and special vascular changes; of creating that state of profound and explosive irritability which has for its psychological concomitant or antecedent an imperious and irresistible craving...Courtship is thus the strong and steady bending of the bow that the arrow may find its mark in a biological end of the highest importance in the survival of a healthy and vigorous race."
Having thus viewed the matter broadly, we may consider in detail a few examples of the process of tumescence among the lower animals and man, for, as will be seen, the process in both is identical. As regards animal courtship, the best treasury of facts is Brehm's _Thierleben_, while Büchner's _Liebe und Liebes-Leben in der Thierwelt_ is a useful summary; the admirable discussion of bird-dancing and other forms of courtship in Häcker's _Gesang der Vögel_, chapter iv, may also be consulted. As regards man, Wallaschek's _Primitive Music_, chapter vii, brings together much scattered material, and is all the more valuable since the author rejects any form of sexual selection; Hirn's _Origins of Art_, chapter xvii, is well worth reading, and Finck's _Primitive Love and Love-stories_ contains a large amount of miscellaneous information. I have preferred not to draw on any of these easily accessible sources (except that in one or two cases I have utilized references they supplied), but here simply furnish illustrations met with in the course of my own reading.
Even in the hermaphroditic slugs (_Limax maximus_) the process of courtship is slow and elaborate. It has been described by James Bladon ("The Loves of the Slug [_Limax cinereus_]," _Zoölogist_, vol. xv, 1857, p. 6272). It begins toward midnight on sultry summer nights, one slug slowly following another, resting its mouth on what may be called the tail of the first, and following its every movement. Finally they stop and begin crawling around each other, emitting large quantities of mucus. When this has constituted a mass of sufficient size and consistence they suspend themselves from it by a cord of mucus from nine to fifteen inches in length, continuing to turn round each other till their bodies form a cone. Then the organs of generation are protruded from their orifice near the mouth and, hanging down a short distance, touch each other. They also then begin again the same spiral motion, twisting around each other, like a two-strand cord, assuming various and beautiful forms, sometimes like an inverted agaric, or a foliated murex, or a leaf of curled parsley, the light falling on the ever-varying surface of the generative organs sometimes producing iridescence. It is not until after a considerable time that the organs untwist and are withdrawn and the bodies separate, to crawl up the suspending cord and depart.
Some snails have a special organ for creating sexual excitement. A remarkable part of the reproductive system in many of the true Helicidæ is the so-called _dart, Liebespfeil_, or _telum Veneris_. It consists of a straight or curved, sometimes slightly twisted, tubular shaft of carbonate of lime, tapering to a fine point above, and enlarging gradually, more often somewhat abruptly, to the base. The sides of the shaft are sometimes furnished with two or more blades; these are apparently not for cutting purposes, but simply to brace the stem. The dart is contained in a dart-sac, which is attached as a sort of pocket to the vagina, at no great distance from its orifice. In _Helix aspersa_ the dart is about five-sixteenths of an inch in length, and one-eighth of an inch in breadth at its base. It appears most probable that the dart is employed as an adjunct for the sexual act. Besides the fact of the position of the dart-sac anatomically, we find that the darts are extended and become imbedded in the flesh, just before or during the act of copulation. It may be regarded, then, as an organ whose functions induce excitement preparatory to sexual union. It only occurs in well-grown specimens. (Rev. L.H. Cooke, "Molluscs," _Cambridge Natural History_, vol. iii, p. 143.)
Racovitza has shown that in the octopus (_Octopus vulgaris_) courtship is carried on with considerable delicacy, and not brutally, as had previously been supposed. The male gently stretches out his third arm on the right and caresses the female with its extremity, eventually passing it into the chamber formed by the mantle. The female contracts spasmodically, but does not attempt to move. They remain thus about an hour or more, and during this time the male shifts the arm from one oviduct to the other. Finally he withdraws his arm, caresses her with it for a few moments, and then replaces it with his other arm. (E.G. Racovitza, in _Archives de Zoölogie Expérimentale_, quoted in _Natural Science_, November, 1894.)
The phenomena of courtship are very well illustrated by spiders. Peckham, who has carefully studied them, tells us of _Saitis pulex_: "On May 24th we found a mature female, and placed her in one of the larger boxes, and the next day we put a male in with her. He saw her as she stood perfectly still, twelve inches away; the glance seemed to excite him, and he at once moved toward her; when some four inches from her he stood still, and then began the most remarkable performances that an amorous male could offer to an admiring female. She eyed him eagerly, changing her position from time to time so that he might be always in view. He, raising his whole body on one side by straightening out the legs, and lowering it on the other by folding the first two pairs of legs up and under, leaned so far over as to be in danger of losing his balance, which he only maintained by sliding rapidly toward the lowered side. The palpus, too, on this side was turned back to correspond to the direction of the legs nearest it. He moved in a semicircle for about two inches, and then instantly reversed the position of the legs and circled in the opposite direction, gradually approaching nearer and nearer to the female. Now she dashes toward him, while he, raising his first pair of legs, extends them upward and forward as if to hold her off, but withal slowly retreats. Again and again he circles from side to side,