Human sexuality does not stand alone. It is part of a wider picture of the sexuality of all other lifeforms. Even plants have male and female parts and reproduce sexually (the new life has characteristics from both parents). The male is the more active part and is proactive in fertilising the female. The female part is fairly static and has the reproductive function of producing the new life. Biological precedents provide crucial evidence for human sexuality. Precedents include the evolution of the erectile sex organ, the male arousal cycle (from erection to ejaculation) and women’s reproductive function.
We share our ancestry with all life on earth. More recently we have ancestors in common with mammals and primates. Mammals have been around for about 225 million years. Primates appeared about 55 million years ago. If a characteristic, such as female orgasm, doesn’t exist in these two groups we need to be able to explain how the human female evolved such a capability.
In other mammals, masturbation is primarily associated with males. Other male mammals masturbate less frequently than human males and less commonly to orgasm. Some female mammals do stimulate their genitals 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 by an attractive female. Within the primates, the male initiates his own genital stimulation and a partner’s. Some females stimulate a male or allow him to stimulate them genitally. This is a behaviour rather than a sign of responsiveness. There are no biological precedents for female orgasm.
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 role in reproduction. 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 experienced 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.
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. It would be very strange if female orgasm were common because it plays no part in human reproduction. The anatomical precedents indicate very clearly that orgasm is achieved through anatomy that parallels the male (the clitoris) rather than anatomy that complements it (the vagina). Even responsive women orgasm sporadically and infrequently (certainly not daily).
Men often conclude that women are sexually repressed. No one explains why only girls are affected by this social pressure. An obvious answer is that girls are impregnated. Rather than being repressed, it’s just common sense. The proposal was that the invention of reliable contraception (primarily the contraceptive pill) would 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 almost 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, some men can be 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 obtains 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. The reward a woman needs to offer to her protector 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 (otherwise parents or society) to raise a child.
Outside of the human species, orgasm is infrequent and possibly absent among females of most species of mammal. (Alfred Kinsey)
Excerpt from Learn About Sexuality (ISBN 978-0956-894748)