Biological precedents provide crucial evidence for human sexuality. The key precedents include the evolution of the sex organs, the male arousal cycle (from erection to ejaculation) and women’s focus on reproduction.
Every embryo has a structure (called the genital tubercle) that becomes the phallus (clitoris or penis). The clitoris is the homologue of the penis. The clitoris has no reproductive function. The vagina, however, plays a crucial role. For impregnation to occur, a man must ejaculate into the vagina. The male and female internal reproductive organs develop from different foetal glands. For the vagina to be involved in female orgasm, male and female responsiveness would have needed to have evolved via totally different routes. Male orgasm is a fundamental response of the human body (since it is critical for reproduction). If women experience a similar response, we would expect it to be the result of a similar physiological process. Nervous excitement in the brain (sexual arousal) causes blood to flow to the phallus.
We share our ancestry with all life on earth. But more recently we had ancestors in common with primates and before that mammals. If a characteristic, such as female orgasm, doesn’t exist in these two groups we need evidence to explain how women might have evolved a capability. Mammals have been around for about 225 million years. Primates appeared about 55 million years ago. There is no evidence to suggest that female mammals orgasm any time. In other mammals, masturbation is primarily associated with males. Some female mammals do masturbate but since they do not ejaculate it is difficult to establish that they ever orgasm.
Only male orgasm is needed for reproduction. In mammals, the male generally initiates the mating act. A male is motivated to mate because he is aroused on seeing a female. Within primates the male initiates his own genital stimulation as well a partner. A few female primates (but not all) stimulate a male or allow a male to stimulate them genitally. This is a behaviour aimed at obtaining male support rather a sign of responsiveness.
While male orgasm (co-incident with ejaculation) is 100% vital to men’s reproductive capability, female orgasm has zero impact on women’s ability to conceive. Women do not have an arousal cycle as men do. It would be very strange if female responsiveness was common because female orgasm plays no part in human reproduction. This is why even responsive women orgasm sporadically and infrequently, with many days or weeks between orgasms. It is likely that female orgasm has become less common over time.
Women are often presumed to suffer from sexual repression. It’s not clear why girls should be affected and not boys. An obvious answer is that girls are impregnated. Rather than being repression, it’s just common sense.
The proposal was that the invention of reliable contraception (primarily the contraceptive pill) could cancel out the effects of millions of years of evolution (from well before homo sapiens) and cause intercourse to become for women exactly what it represented for men: an opportunity to enjoy erotic pleasure, arousal and orgasm. It is not possible for women to evolve a sex drive overnight just because they have reliable contraception.
A man’s key reproductive priority is to maximise his ejaculations (into a vagina) and increase his chances of procreating. Male responsiveness arises because male orgasm triggers ejaculation of sperm. Women’s top reproductive priority is to find a mate who will be dedicated to protecting and supporting her through the long process of bearing and raising a child.
A man gives through his role as protector (where a man supports the family) and defender (where a man risks his life). Families depend on men for protection. But men are inclined to take risk. This means that men often represent the greatest threat to women and children in the first place. Most of the time men have little interest in women, so when a man notices her, a woman is complimented especially if he is successful. If a woman sees an advantage in having a man’s protection, she may be motivated to please him.
Women may flirt to indicate their amenability to a man they admire. This is a conscious behaviour and not a sign of sexual arousal. Women have learned that when they offer intercourse, men are generous in return. So women have an incentive to offer intercourse regardless of their own pleasure. If a woman depends on a man’s willingness to fight or earn, it is difficult for her to complain when he wants the intimacy he needs from sex.
Women need men for two reasons. A woman needs a man to protect her (against other men) and to support her while she raises children. Most animals (carnivores) only kill to eat. Men (and other male primates) kill their own kind. Women have needed to find a capable man to protect them and the reward she needs to offer is regular intercourse. Other female mammals raise their young alone (with no assistance from the male). Human offspring need a mother’s care for much longer than other animals because of the complexity of the human brain. In modern times, a woman still needs support from a man (parents or society) to raise children.
Outside of the human species, orgasm is infrequent and possibly absent among females of most species of mammal. (Alfred Kinsey 1953)