Why is Sex Fun - by Jared Diamond


Why is Sex Fun - by Jared Diamond

Read: 2023-12-05

Recommend: 8/10

I like the evolutionary approach to human sexuality in this book. I do understand myself and others around me better after reading this book.



Here are some text that I highlighted in the book:

  1. this book may help you understand why your body feels the way it does, and why your beloved is behaving the way he or she is. Perhaps, too, if you understand why you feel driven to some self-destructive sexual behavior, that understanding may help you to gain distance from your instincts and to deal more intelligently with them.

  2. Increasingly today, we consider it narrow-minded and despicably prejudiced to denigrate those who do not conform to our own standards. Each such form of narrow-mindedness is associated with a despicable “ism”—for instance, racism, sexism, Eurocentrism, and phallocentrism. To that list of modern “ism” sins, defenders of animal rights are now adding the sin of species-ism.

  3. let’s consider normal sexuality by the standards of the world’s approximately 4,300 species of mammals, of which we humans are just one.

  4. The following human attributes are among those that we take for granted as normal:

    1. 1: Most men and women in most human societies end up in a long-term pair relationship (“marriage”)
    2. 2: In addition to being a sexual union, marriage is a partnership for joint rearing of the resulting babies.
    3. 3: Despite forming a couple (or occasionally a harem), a husband and wife (or wives) do not live (like gibbons) as a solitary couple in an exclusive territory that they defend against other couples, but instead they live embedded in a society of other couples with whom they cooperate economically and share access to communal territory.
    4. 4: Marriage partners usually have sex in private, rather than being indifferent to the presence of other humans.
    5. 5: Human ovulation is concealed rather than advertised. That is, human sex is mostly for fun, not for insemination.
    6. 6: All women who live past the age of forty or fifty undergo menopause, a complete shutdown of fertility. Men in general do not undergo menopause
  5. Suppose that opportunities to transmit genes arise unpredictably and infrequently, and that the number of offspring produced by such opportunities increases with the female’s nutritional condition. That’s the case for some species of spiders and mantises living at low population densities. A male is lucky to encounter a female at all, and such luck is unlikely to strike twice. The male’s best strategy is to produce as many offspring bearing his genes as possible out of his lucky find. The larger a female’s nutritional reserves, the more calories and protein she has available to transform into eggs. If the male departed after mating, he would probably not find another female and his continued survival would thus be useless. Instead, by encouraging the female to eat him, he enables her to produce more eggs bearing his genes. In addition, a female spider whose mouth is distracted by munching a male’s body allows copulation with the male’s genitalia to proceed for a longer time, resulting in more sperm transferred and more eggs fertilized.

  6. Though seemingly remote from human sexuality, shorebird sexuality is instructive because it illustrates the main message of this book: a species’ sexuality is molded by other aspects of the species’ biology. It’s easier for us to acknowledge this conclusion about shorebirds, to which we don’t apply moral standards, than about ourselves.

  7. Given these cruel statistics, why should any female accept the fate of being the “other woman”? Biologists used to speculate that secondary females choose their fate, reasoning that the neglected second spouse of a good male is better off than the sole spouse of a lousy male with a poor territory. (Rich married men have been known to make similar pitches to prospective mistresses.) It turns out, though, that the secondary females do not accept their fate knowingly but are tricked into it. The key to this deception is the care that polygynous males take to set up their second household a couple of hundred yards from their first household, with many other males’ territories intervening. It’s striking that polygynous males don’t court a second spouse at any of dozens of potential nest holes near the first nest, even though they would thereby reduce their commuting time between nests, have more time available to feed their young, and reduce their risk of being cuckolded while en route. The conclusion seems inescapable that polygynous males accept the disadvantage of a remote second household in order to deceive the prospective secondary mate and conceal from her the existence of the first household. Life’s exigencies make a female Pied Flycatcher especially vulnerable to being deceived. If she discovers after egg-laying that her mate is polygynous, it’s too late for her to do anything about it. She’s better off staying with those eggs than deserting them, seeking a new mate from the males now available (most of them are would-be bigamists anyway), and hoping the new mate will prove to be any better than the former one.

  8. A man who opts for child care runs the risk that, unbeknownst to him, his efforts are transmitting the genes of a rival. This biological fact is the underlying cause for a host of repulsive practices by which men of various societies have sought to increase their confidence in paternity by restricting their wife’s opportunity for sex with other men. Among such practices are high bride prices only for brides delivered as proven virgin goods; traditional adultery laws that define adultery by the marital status only of the participating woman (that of the participating man being irrelevant); chaperoning or virtual imprisonment of women; female “circumcision” (clitoridectomy) to reduce a woman’s interest in initiating sex, whether marital or extramarital; and infibulation (suturing a woman’s labia majora nearly shut so as to make intercourse impossible while the husband is away).

  9. All three factors—sex differences in obligate parental investment, alternative opportunities foreclosed by child care, and confidence in parenthood—contribute to making men much more prone than women to desert a spouse and child.

  10. Because a human child virtually required paternal care in traditional human societies, extramarital sex is most profitable for a man if it is with a married woman whose husband will unknowingly rear the resulting child. Casual sex between a man and a married woman tends to increase the man’s output of children, but not the woman’s. That decisive difference is reflected in men’s and women’s differing motivations. Attitude surveys in a wide variety of human societies around the world have shown that men tend to be more interested than women in sexual variety, including casual sex and brief relationships. That attitude is readily understandable because it tends to maximize transmission of the genes of a man but not of a woman. In contrast, the motivation of a woman participating in extramarital sex is more often self-reported as marital dissatisfaction. Such a woman tends to be searching for a new lasting relationship: either a new marriage or a lengthy extramarital relationship with a man better able than her husband to provide resources or good genes.

  11. As a major cause of infant death, infanticide is a serious evolutionary problem for animal mothers, who thereby lose their genetic investment in murdered offspring. For instance, a typical female gorilla over the course of her lifetime loses at least one of her offspring to infanticidal intruding male gorillas attempting to take over the harem to which she belongs. Indeed, over one-third of all infant gorilla deaths are due to infanticide.

  12. While no male can then be confident of his paternity, many males recognize that they might have sired the mother’s eventual infant. If such a male later succeeds in driving out the mother’s consort and taking her over, he avoids killing her infant because it could be his own. He might even help the infant with protection and other forms of paternal care. The mother’s concealed ovulation will also serve to decrease fighting between adult males within her troop because any single copulation is unlikely to result in conception and hence is no longer worth fighting over.

  13. females may thus use concealed ovulation to confuse paternity

  14. [many-fathers theory] It turned out that females started to copulate long before they ovulated, continued long after they ovulated, and did not reach their peak sexual receptivity until the first half of pregnancy. At that time the female’s belly was not yet visibly bulging, and the deceived males had no idea that they were utterly wasting their efforts. Females finally ceased copulating during the latter half of pregnancy, when the males could no longer be deceived. That still left most males in the troop ample time to have sex with most of the troop’s females. One-third of the males were able to copulate with every single female. Thus, through concealed ovulation female vervets ensured the benevolent neutrality of almost all of the potentially murderous males in their immediate neighborhood.

  15. Natual selection has not programmed menopause into men because of three more cruel facts: men never die in childbirth and rarely die while copulating, and they are less likely than mothers to exhaust themselves caring for infants.

  16. If we think that we have a signaling system immune to cheating, why do so many people resort to makeup, hair dyes, and breast augmentation? As for our supposedly wise and careful selection process, all of us know that when we walk into a room full of unfamiliar people, we quickly sense who attracts us physically and who doesn’t. That quick sense is based on “sex appeal,” which just means the sum of the body signals to which we respond, largely unconsciously. Our divorce rate, now around 50 percent in the United States, shows that we ourselves acknowledge the failure of half of our efforts to select mates.

  17. the face is the part of the body most sensitive to the ravages of age, disease, and injury. Especially in traditional societies, individuals with scarred or misshapen faces may thereby be advertising their proneness to disfiguring infections, inability to take care of themselves, or burden of parasitic worms. A beautiful face was thus a truthful signal of good health that could not be faked until twentieth-century plastic surgeons perfected facelifts.

  18. large fatty breasts are not only an honest signal of good overall nutrition but also a deceptive specific signal of high milk-producing ability (deceptive because milk is actually secreted by breast glandular tissue rather than by breast fat). Similarly, it has been suggested that fat deposition in the hips of women worldwide is also both an honest signal of good health and a deceptive specific signal suggesting a wide birth canal (deceptive because a truly wide birth canal would minimize the risk of birth traumas but mere fat hips would not).

  19. Like humans, chimpanzees and baboons and macaques live in troops and have sexually ornamented females (as well as males). By contrast, female gibbons and the females of other primate species that live as solitary male-female pairs bear little or no sexual ornamentation. This correlation suggests that if and only if females compete intensively with other females for males’ attention—for example, because multiple males and females encounter each other daily in the same troop—then females tend to evolve sexual ornamentation in an ongoing evolutionary contest to be more attractive. Females who do not have to compete on such a regular basis have less need of expensive body ornamentation.

  20. Are those extra couple of inches of the human penis a functionally unnecessary luxury? One counterinterpretation is that a large penis might somehow be useful in the wide variety of our copulatory positions compared to many other mammals. However, the 1½-inch penis of the male orangutan permits it to perform in a variety of positions that rival ours, and to outperform us by executing all those positions while hanging from a tree. As for the possible utility of a large penis in sustaining prolonged intercourse, orangutans top us in that regard too (mean duration fifteen minutes, versus a mere four minutes for the average American man).

  21. What remains debatable is the intended audience at which the penis’s proclamation of virility is directed. Most men would assume that the ones who are impressed are women. However, women tend to report that they are more turned on by other features of a man, and that the sight of a penis is, if anything, unattractive. Instead, the ones really fascinated by the penis and its dimensions are men. In the showers in men’s locker rooms, men routinely size up each other’s endowment. Even if some women are also impressed by the sight of a large penis or are satisfied by its stimulation of the clitoris and vagina during intercourse (as is very likely), it is not necessary for our discussion to degenerate into an either/or argument that assumes the signal to be directed at only one sex. Zoologists studying animals regularly discover that sexual ornaments serve a dual function: to attract potential mates of the opposite sex, and to establish dominance over rivals of the same sex. In that respect, as in many others, we humans still carry the legacy of hundreds of millions of years of vertebrate evolution engraved deeply into our sexuality. Over that legacy, our art, language, and culture have only recently added a veneer.