Our own species has made a radical change in its typical body posture. Like geladas, we spend a great deal of time sitting up vertically. We also stand erect and face one another during social contacts. Could it be, then, that we, too, have indulged in something similar in the way of self-mimicry? Could our vertical I posture have influenced our sexual signals? When considered in this way the answer certainly seems to be yes. The typical mating posture of all other primates involves the rear approach of the male to the female. She lifts her rear end and directs it towards the male. Her genital region is visually presented backwards to him. He sees it, moves towards her, and mounts her from behind. There is no frontal body contact during copulation, the male’s genital region being pressed on to the female’s rump region. In our own species the situation is very different. Not only is there prolonged face-to-face pre-copulatory activity, but also copulation itself is primarily a frontal performance.
There has been some argument about this last point. It is a long-standing idea that the face-to-face mating position is the biologically natural one for our species, and that all others should be considered as sophisticated variations of it. Recent authorities have challenged this and have claimed that there is no such thing as a basic posture as far as we are concerned. Any body relationship, they feel, should be grist to our sexual mill, and as an inventive species it should be natural for us to experiment with any postures we like—the more the better, in fact, because this will increase the complexity of the sexual act, increase sexual novelty, and prevent sexual boredom between the members of a long-mated pair. Their argument is a perfectly valid one in the context within which they present it, but in trying to score their point they have gone too far. Their real objection was to the idea that any variations of the basic posture are ‘sinful’. To counteract this idea, they stressed the value of these variations, and were quite right to do so, for the reasons given. Any improvement in sexual rewards for the members of a mated pair will obviously be important in strengthening the pair-bond. They are biologically sound for our species. But in fighting this battle the authorities concerned lost sight of the fact there is nevertheless one basic, natural mating posture for our species—the face-to-face posture. Virtually all the sexual signals and erogenous zones are on the front of the body—the facial expressions, the lips, the beard, the nipples, the areolar signals, the breasts of the female, the pubic hair, the genitals themselves, the major blushing areas, and the major sexual flush areas. It could be argued that many of these signals would operate perfectly well in the earlier stages, which could be face-to-face, but then, for the copulation itself, with both partners now fully aroused by frontal stimulation, the male could shift into a rear position for rear entry copulation, or, for that matter, into any other unusual posture he cared to select. This is perfectly true, and possible as a novelty device, but it has certain disadvantages. To start with, the identity of the sexual partner is much more important to a pair-bonding species like ours. The frontal approach means that the in-coming sexual signals and rewards are kept tightly linked with the identity signals from the partner. Face-to-face sex is ‘personalised sex’. In addition, the pre-copulatory tactile sensation from the frontally concentrated erogenous zones can be extended into the copulatory phase when the mating act is performed face-to-face. Many of these sensations would be lost by adopting other postures. Also, the frontal approach provides the maximum possibility for stimulation of the female’s clitoris during the pelvic thrusting of the male. It is true that it will be passively stimulated by the pulling effect of the male’s thrusts, regardless of his body position in relation to the female, but in a face-to-face mating there will in addition be the direct rhythmic pressure of the male’s pubic region on to the clitoral area, and this will considerably heighten the stimulation. Finally, there is the basic anatomy of the female vaginal passage, the angle of which has swung forward to a marked degree, when compared with other species of primates. It has moved forward more than would be expected simply as a passive result of the process of becoming a vertical species. Undoubtedly, if it had been important for the female of our species to present her genitals to the male for rear mounting, natural selection would soon have favoured that trend and the females would by now have a more posteriorly directed vaginal tract.
So it seems plausible to consider that face-to-face copulation is basic to our species. There are, of course, a number of variations that do not eliminate the frontal element: male above, female above, side by side, squatting, standing, and so on, but the most efficient and commonly used one is with both partners horizontal, the male above the female. American investigators have estimated that in their culture 70 per cent of the population employ only this position. Even those w o vary their postures still use the basic one for much of the time. Fewer than ten per cent experiment with rear-entry positions. In a massive, cross-cultural survey involving nearly two hundred different societies scattered all over the world, the conclusion was that copulation with the male entering the female from the rear does not occur as the usual practice in any of the communities studied.
If we can now accept this fact, we can return from this slight digression to the original question concerning sexual self-mimicry. If the female of our species was going to successfully shift the interest of the male round to the front, evolution would have to do something to make the frontal region more stimulating. At some point, back in our ancestry, we must have been using the rear approach, supposing we had reached the stage where the female signalled sexually to the male from behind with a pair of fleshy, hemispherical buttocks (not, incidentally found elsewhere amongst the primates) and a pair of bright red genital lips, or labia, supposing the male had evolved a powerful sexual responsiveness to these specific signals. Supposing that, at this point in evolution, the species became increasingly vertical and frontally orientated in its social contacts. Given this situation, one might very well expect to find some sort of frontal self-mimicry of the type seen in the gelada baboon. Can we, if we look at the frontal regions of the females of our species, see any structures that might possibly be mimics of the ancient genital display of hemispherical buttocks and red labia? The answer stands out as dearly as the female bosom itself. The protuberant, hemispherical breasts of the female must surely be copies of the fleshy buttocks, and the sharply defined red lips around the mouth must be copies of the red labia. (You may recall that, during intense sexual arousal, both the lips of the mouth and the genital labia become swollen and deeper in colour, so that they not only look alike, but also change in the same way in sexual excitement.) If the male of our species was already primed to respond sexually to these signals when they emanated posteriorly from the genital region, then he would have a built-in susceptibility to them if they could be reproduced in that form on the front of the female’s body. And this, it would seem, is precisely what has happened, with the females carrying a duplicate set of buttocks and labia on their chests and mouths respectively. (The use of lipsticks and brassieres immediately springs to mind, but these must be left until later, when we are dealing with the special sexual techniques of modern civilisation.)
In addition to the all-important visual signals, there are certain odour stimuli that play a sexual role. Our sense of smell has been considerably reduced during evolution, but it is reasonably efficient and is more operative during sexual activities than we normally realise. We know that there are sex differences in body odours and it has been suggested that part of the process of pair-formation—falling in love—involves a kind of olfactory imprinting, a fixation on the specific individual odour of the partner’s body. Connected with this is the intriguing discovery that at puberty there is a marked change in odour preferences. Before puberty there are strong preferences for sweet and fruity odours, but with the arrival of sexual maturity this response falls off and there is a dramatic shift in favour of flowery, oily and musky odours. This applies to both sexes, but the increase in musk responsiveness is stronger in males than females. It is aimed that as adults we can detect the presence of musk even when it is diluted down to one part in eight million parts of air, and it is significant that this substance plays a dominant role in the scent-signalling of many mammalian species, being produced in specialised scent-glands. Although we ourselves do not possess any large scent glands, we do have a large number of small ones—the apocrine glands. These are similar to ordinary sweat glands, but their secretions contain a higher proportion of solids. They occur on a number of parts of the body, but there are specially high concentrations of them in the regions of the armpits and the genitals. The localised hair-tufts that grow in these areas undoubtedly function as important scent-traps. It has been claimed that scent production in these areas is heightened during sexual arousal, but no detailed analysis of this phenomenon has yet been made. We do, however, know that there are 75 per cent more apocrine glands in the female of our species than in the males it is interesting to recall that in lower mammals during sexual encounters the male sniffs the female more than she sniffs him.
The location of our specialised odour-producing areas appears to be yet another adaptation to our frontal approach to sexual contact. There is nothing unusual about the genital centre, this we have in common with many other mammals, but the armpit concentration is a more unexpected feature. It appears to relate to the general tendency in our species to add new sexual stimulation centres to the front end of the body, in connection with the great increase in face-to-face sexual contacts. In this particular case it would result in the partner’s nose being kept in close proximity with a major scent-producing area throughout much of the pre-copulatory and copulatory activity.
Up to this point we have been considering ways in which the appetitive sexual behaviour of our species has been improved and extended, so that contacts between the members of a mated pair have become increasingly rewarding, and their pair-bond therefore strengthened and maintained. But appetitive behaviour leads to a consummatory act and some improvements have been needed here too. Consider for a moment the old primate system. The adult males are sexually active all the time, except when they have lour ejaculated. A consummatory orgasm is valuable for them because the relief from sexual tension that it brings damps down their sexual urges long enough for their sperm supplies to be replenished. The females, on the other hand, are sexually active only for a limited period centred around their ovulation time. During this period they are ready to receive the males at any time. The more copulations they experience, the greater the insurance that successful fertilisation will be achieved. For them, there is no sexual satisfaction, no moment of copulatory climax that would pacify and tame their sexual urges. While they are on heat, there is no time to lose, they must keep going at all costs. If they experienced intense orgasms, they would then waste valuable potential mating time. At the end of a copulation, when the male and dismounts, the female monkey shows little sign of emotional upheaval and usually wanders off as if nothing had happened.
With our own pair-bonding species the situation is entirely different. In the first place, as there is only a single male involved, there is no particular advantage in the female being sexually responsive at the point where he is sexually spent. So there is nothing working against the existence of a female orgasm. There are, however, two things working very much in its favour. One is the immense behavioural reward it brings to the act of sexual co-operation with the mated partner. Like all the other improvements in sexuality this will serve to strengthen the pair-bond and maintain the family unit. The other is that it considerably increases the chances of fertilisation. It does this in a rather special way that applies only to our own peculiar species. Again, to understand this, we must look back at our primate relatives. When a female monkey has been inseminated by a male, she can wander away without any fear of losing the seminal fluid that now lies in the innermost part of her vaginal tract. She walks on all fours. The angle of her vaginal passage is still more or less horizontal. If a female of our own species were so unmoved by the experience of copulation that she too was likely to get up and wander off immediately afterwards, the situation would be different, for she walks bipedally and the angle of her vaginal passage during normal locomotion is almost vertical. Under the simple influence of gravity the seminal fluid would flow back down the vaginal tract and much of it would be lost. There is therefore a great advantage in any reaction that tends to keep the female horizontal when the male ejaculates and stops copulating. The violent response of female orgasm, leaving the female sexually satiated and exhausted, has precisely this effect. It is therefore doubly valuable.
The fact that the female orgasm in our species is unique amongst primates, combined with the fact that it is physiologically almost identical with the orgasmic pattern of the male, suggests that perhaps it is in an evolutionary sense a ‘pseudo-male’ response. In the make-up of both males and females there are latent properties belonging to the opposite sex. We know from comparative studies of other groups of animals that evolution can, if necessary, call up one of these latent qualities and bring it into the front line (in the ‘wrong’ sex, as it were). In this particular instance we know that the female of our species has developed a particular susceptibility to sexual stimulation of the clitoris. When we remember that this organ is the female homologue, or counterpart, of the male penis, this does seem to point to the fact that, in origin at any rate, the female orgasm is a ‘borrowed’ male pattern. This may also explain why the male has the largest penis of any primate. It is not only extremely long when fully erect, but also very thick when compared with the penises of other species. (The chimpanzee’s is a mere spike by comparison.) This broadening of the penis results in the female’s external genitals being subjected to much more pulling and pushing during the performance of pelvic thrusts. With each inward thrust of the penis, the clitoral region is pulled downwards and then, with each withdrawal, it moves up again. Add to this the rhythmic pressure being exerted on to the clitoral region by the pubic region of the frontally copulating male, and you have a repeated massaging of the clitoris that—were she a male—would virtually be masturbatory.