Biological Basis of Sex Appeal


Richard F. Taflinger

Part Two of a Two Part Discussion

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All of the information in Part One applies to human reproductive strategy. Men are basically promiscuous; women are basically selective. Male criteria are physical; female criteria are physical and social. Men compete with each other for women's attention; women select those men who win competitions. There are, however, major modifying factors in human strategy that make humans unique among the animals. The first is the human mind, which I will discuss later. The second is the human anatomy, equally unique, which I will discuss now.

Anatomy and Sex

Human anatomy differs rather radically from that of other mammals, in particular other primates. This difference has a major effect on how humans approach sex.

The biology, anatomy and physiology of most mammalian life on Earth lead to an instinctive approach. The biological imperatives guide male and female sexual behavior, and anatomy does nothing to impede that behavior. Note I say "most". There is one notable exception: human beings.

Typical land mammalian anatomical structure enhances rather than impedes reproduction.(8) For example, let's examine a typical female land mammal. She walks on all fours, her rear legs at right angles to her spine. Her vagina is under her tail and flush to the surface.

What these factors mean is significant. First, the male mounts from the rear for sexual intercourse. He approaches from the rear, places his weight on her back, and engages. The technical term for this is lordosis. (Beach, 1968; Morgan, 1972)

The position of her limbs makes it possible for her to support his weight during intercourse without a lot of effort. Her limbs don't impede intercourse. In addition, if she is not ready she can simply walk away.

The effort she must expend in intercourse is also reduced (remember how important her effort is biologically). She need only stand still and let him do the work.

Of course, animals don't engage in mating all the time. So for mammals, the vagina, a very delicate organ, is well protected by the tail or by the hip and leg structure. Nonetheless, during mating it is easily accessible.

Some of you may be thinking, "What has this to do with humans? Humans aren't built anything at all like deer or cows or horses. What about primates, which humans are like?"

Very well, what are primates like? Well, very much like deer or cows or horses. They primarily walk on all fours, males mount from the rear, her limbs can easily take his weight during intercourse and have great lateral flexibility. Her vagina is near the tail bone and on the surface, easily accessible to the male when she presents her posterior. The position of her limbs and a callosity on her rump also protect it when she sits. Thus, technique hasn't changed from deer to chimp.(9)

It is when we begin to examine human sexual anatomy that problems become apparent. The human body seems designed to impede rather than enhance intercourse.

Most of the differences between non-human and human anatomy that are important to this discussion are in the female structure. First, and most obvious, is the human upright stance. Only humans normally walk on their hind legs rather than on all fours and have the hip and leg structures that make it easy and natural. For males, this causes little in the way of problems since he's convex rather than concave.

For females, however, it is a major problem. As her legs rotated about her hips, moving from a right angle to in-line with her spine, her vaginal opening traveled farther and farther forward. Also, instead of being surface mounted, like other land mammals, her vagina retreated into her body with a covering of extra flesh. (Hamburg, 1974)

There were not only changes in the position of her vagina. Her legs changed radically as well from those of all other primates. First, her legs got closer and closer together. Second, her hip joints reformed to reduce lateral flexibility and stabilize her upright posture. Finally, instead of the spindly, bowed leg structure that all other primates had and have, her legs turned into long, thick, heavy, muscular columns.

A last major change in her anatomy was her buttocks. Unlike any other creature on earth, including the primates, humans have big buttocks, sometimes so large they form a shelf in the back. And it is almost axiomatic that no matter the race or culture, the female will have a bigger behind than the male.

At this point you may very well be asking yourself, "So what? So women have large buttocks -- so do men. So women walk upright -- so do men. What's the big deal?"

It's a good question. The answer is that as the female primate changed into the female human, her new body made sex difficult. Her vagina was now not easily accessible but difficult to get to. It moved far forward, got a covering layer of flesh, and became hidden between two heavy columns of bone and muscle.

"Nonsense!" you reply. "Where do all these babies come from, if sex is impossible? Men and women do get together, you know."

Indeed, they do, but not the way almost any other primate or land mammal does. Remember, all these changes in female anatomy occurred before humans became human. Let's examine what may have happened long ago and far away.

Ms. Primate, decked out in her new body, bounds up to a likely looking male and presents her posterior -- after all, land mammals mate from the rear. He, of course, responds. However, there is a new and frustrating development -- he can't reach. Equipped as he is with a primate penis, which is small,(10) her vagina is too far forward, her legs too close together, and her buttocks hold him too far away.

"Then the human race died out," you sneer sarcastically, knowing such is not the case. Obviously the human race did not die out. To avoid this fate, the male primate had two choices: evolve physically to compensate for her changes, or change his technique. In fact, the male did both.

First, the proto-human male evolved an over-sized penis, the largest in the primate world, and one of the largest in comparison to body size in nature.(11) However, since this evolution in male structure was in response to changes in the female, he was always a little behind (no pun intended).

It was his solution to this problem that has had a great influence on human male and female attitudes towards sex -- he changed his technique.


To understand the significance of his changing his technique, we must examinesome aspects of animal behavior, in particular aggression and appeasement. First, some definitions: what do I mean by aggression and appeasement. The modern definition of aggression is a cultural, rather than a biological one. Today, "aggression" means the deliberate infliction of harm on someone or something else. However, biological aggression is an organism's assertion of itself to gain survival or reproductive rights. Aggression can result in the infliction of harm on something else, but not necessarily. For example, the baboon male can assert itself simply by flashing its eyelids and yawning. He doesn't have to move at all, and no other baboon suffers the slightest physical harm (it may cause a certain loss of self-esteem for the other baboon, but nothing more). Only in extreme cases, such as the vicious mating fights of elephant seals (LeBoeuf, 1974), does physical chastisement that causes great injury to other members of the group occur.

Every animal, if it is to ensure that its genes get passed on, must have a degree of aggression. It must assert itself as the most deserving of procreation; animals that do not assert themselves end themselves.

However, the aggression towards other members of an animal's own species is usually limited. For example, the males' mating battles may appear vicious and aimed at killing each other. True, the fight may severely injure one or both, and one or both may later die of his wounds or exhaustion. However, one actually killing the other during combat is rare.

In most instances, when one of the contenders has had enough, he will run away or make an appeasement signal. If he runs, the winner may chase him for a short distance, and then the battle is forgotten -- there are no grudges held (unless, of course, the loser comes back again and again, in which case the winner delivers a more definite lesson). If the loser makes an appeasement signal, it may be exposing the throat, lying down on his back, or otherwise exposing himself to a killing stroke from the winner. (Morgan, 1972) However, the killing stroke doesn't come -- the winner accepts the loser's capitulation and stops attacking.

The limits on aggression are instinctive and immediate; a winner does not continue an attack after the loser submits or runs away, does not carry a grudge, does not try to gain revenge. Intraspecies aggression is to establish status, breeding rights, or to chastise improper behavior (that which may endanger the species). Once an animal submits, the aggressor stops the attack and backs off; he or she has no choice -- an animal cannot fight instinct.

Such behavior is vital if a species is to avoid killing itself off. It is particularly important in those species that nature has equipped with deadly weapons such as long, pointy teeth and claws.

Now let's examine what all this means to Ms. and Mr. Protohuman. They, like other animals, must have had a degree of aggression to survive. Those that were most capable of wresting a living from the environment and procreating were the most successful.

Protohumans were undoubtedly as social as primates are today. (Leakey, 1977) Thus, they probably used aggression on each other to establish status, breeding rights, and to chastise.

The protohuman was small, perhaps no more than three and a half to four feet tall, (Leakey, 1977) and lacked much in the way of natural weapons. Thus, although they must have had aggression and appeasement signals like all animals, they were probably rather weak, strong signals only needed when one animal can easily kill another. Nonetheless, they must have been strong enough to avoid having one kill another through ignoring appeasement.

"What does all this have to do with the male changing his technique?" you may ask. Let's get back to the scenario and see what happens next.

She has presented her posterior and he tries to respond. However, her newly arranged and pneumatic body prevents his success. Now, what happens if some bright boy comes up with a flash of brilliance: "If I can't reach from this side, how about if I try from the other?" Carrying out his brilliant plan, he flips her on her back, spreads her legs, and tries again.

This is fine for him. However, what is her reaction? Remember, up to this time, all mating has been from the rear. For him to flip her on her back and get on top of her must mean, to her, that he is attacking, not mating. On her back her soft belly is unprotected, she can't run, her legs are unavailable since he's between them. In other words, she's scared out of her little protohuman mind.

She has two choices: fight back, or submit. If she fights back, he fights as well. Since he is probably bigger and stronger, if only slightly, he will probably win. She will thus fall back on choice two -- she submits and makes appeasement signals.

Now is when things get weird. She submits, making appropriate appeasement signals. He, following instinct triggered by her signals, immediately stops what he is doing and backs away. It doesn't matter that he wasn't actually attacking. What does matter is she made appeasement signals and he must back away.

She, of course, is bewildered. She was all set for the undoubtedly enjoyable activity of sex. Suddenly, he attacks her. What's the matter with him?

He's even more confused. She came up obviously prepared for fun. He was of like mind. However, he has difficulties because of her changed anatomy that he hasn't adapted to yet. He came up with the perfect solution, and she immediately tried to fight him off. What's the matter with her? Then, when she stopped fighting, he instantly lost interest. What's the matter with him? What's the matter with this whole business?

However, this was the story of Mr. A. What about Mr. B? Same scenario, but when she makes appeasement signals, Mr. B reacts. However, unlike Mr. A, he does not back off, but continues until orgasm. Why? His instinctual reaction to appeasement signals is weak; they do not instantly turn off his actions. The upshot is Mr. A and his genes die out; Mr. B and his genes continue. Enough Mr. Bs and the instinct for stopping aggressive behavior when opponents surrender is bred out of the species. Aggression is also bred into sex. This is not that unusual. For example, "The female blue heron hears the love screech of the male. She picks her heart's desire and settles on a branch nearby. The male immediately begins to court her. The moment she indicates interest and approaches him, though, he changes hismind, becomes unpleasant, shoos her away, or even attacks her. As soon as the discourage female flies off, he screeches after her... If she gives him another chance and flies back, he may very well attack her again. Gradually, though, should the female's patience last that long, the fickle male's grumpiness subsides and he may actually be ready to mate. He is conflicted and ambivalent. Sex and aggression are mixed up in his mind, and the confusion is so profound that, if not for the patience of the female, this species might fail to reproduce itself... But a similar confusion in the minds especially of males holds for many species, including reptiles, birds, and mammals. Some the the brain's neural circuitry for aggression seems dangerously cheek by jowl with the neural circuitry for sex. The resulting behavior is strangely familiar. But of course humans are not herons." (Sagan & Druyan, 1992, p. 191)

All this from human females standing up and growing buttocks? Yes. Why those features? There are many theories, many of which seem to say that females grew these and other features, such as breasts, ear lobes and plump lips to be more appealing to the males, to make sex sexier (most of these theories have been advanced by male anthropologists, such as Desmond Morris in his THE NAKED APE, an interesting point for speculation). I reply, hogwash. Evolution does not create major structural changes in animals to make them sexier and at the same time make sex more difficult physically, and by extension psychologically. Besides, what was wrong with the old features? Chimps and baboons still have them and they don't seem to find each other unattractive. Warthogs find other warthogs attractive without buttocks and large, well-rounded breasts, too.

No, evolution creates changes that improve chances for survival; if the changes don't contribute to survival, the animal carrying them dies out. Why these changes occurred doesn't concern us, are a matter of controversy, and in any case would take too long to explain in an advertising book.(12) Suffice it to say, nature thought they were necessary to improve the female's, and by extension her offsprings', chance of survival.

However, convenience doesn't figure into evolution. An animal either adapts to the changes or dies out. Such is the case with protohumans, their anatomy and their sex lives -- the changes contributed to survival, they adapted to the inconvenience. That adaptation to inconvenience has guided human reproductive strategy, and scarred relations between the sexes, ever since. However, as long as babies are born, nature doesn't care.


The above is a look at the biology of human reproduction. However, as mentioned earlier, humans have something that no other animal has, and that has a greater effect on reproduction strategy than any other animal -- the human mind. I will discuss that in the next chapter, under REPRODUCTION AND SOCIETY.

8 Note that I refer to land mammals. There are, of course, aquatic mammals such as whales, dolphins and seals. However, since very little advertising is aimed at them, I will confine discussion to land mammals.

9 Gibbons, which hang by their arims during mating, mate face to face. Bonobos (pygmy chimps) also occasionally mae face to face, but the usual method is lordosis.

10 The gorilla's erect penis averages only 2 inches in length.

11 The flea has one 15 times his own body length, something that would give any man an inferiority complex.

12 If you're interested in one possible explanation, one that most anthropologists dismiss as untenable but is entertaining, see Elaine Morgan's THE DESCENT OF WOMAN. If nothing else, it avoid the underlying, subconscious male bias of many attempts to explain why humans are physically so different from other primates.

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