Sex at Dawn is a book written by Dr. Christopher Ryan and Dr. Cacilda Jethá. This post has my notes from the book.
• Before the advent of agriculture, universal and culturally imposed sharing was the most effective way for our species to minimize risk.
• Our pre-agricultural ancestors lived in groups where most mature individuals would have had several ongoing sexual relationships at any given time. These relationships reinforced crucial social ties holding highly interdependent communities together.
• Hunter-gatherer societies have mandatory sharing. Hoarding or hiding food is considered deeply shameful.
• Many explorers, missionaries, and anthropologists have documented mate sharing among foraging societies and an open sexuality unencumbered by guilt or shame.
• Kinship ties, social rank, sexual attractiveness, and individual sexual preferences influence mate choice in primates.
• Our DNA differs from that of chimpanzees and bonobos by only 1.6 percent.
• Monogamy is not found in any social, group-living primate.
• Female chimpanzees and bonobos engage in multiple mating sessions in quick succession with different males.
• A study of DNA samples taken from hair follicles collected from chimpanzee nests at one study area showed that more than half the young had been fathered by males from outside the female’s home group.
• Humans and bonobos share a repetitive microsatellite at gene AVPR1A, which is has a significant role in the release of oxytocin. Oxytocin is important in pro-social feelings like compassion, trust, generosity, love, and eroticism.
• Similarities between humans and bonobos:
1. Human and bonobo females copulate throughout the menstrual cycle, as well as during lactation and pregnancy.
2. Human and bonobo infants develop much more slowly than chimpanzees.
3. Like humans, female bonobos return to the group immediately after giving birth and copulate within months.
4. Bonobos and humans enjoy many different copulatory positions, with ventral-ventral (missionary position) appearing to be preferred by bonobo females and rear-entry by males.
5. Bonobos and humans often gaze into each other’s eyes when copulating and kiss each other deeply.
6. The vulva is located between the legs and oriented toward the front of the body in humans and bonobos.
7. Food sharing is highly associated with sexual activity in humans and bonobos.
8. There is a high degree of variability in potential sexual combinations in humans and bonobos.
9. While sexual activity in chimps and other primates appears to be primarily reproductive, bonobos and humans utilize sexuality for social purposes (tension reduction, bonding, conflict resolution, entertainment, etc.)
• Women in South American and Polynesian societies will seek out sex with an assortment of men. She’ll solicit “contributions” from the best hunters, the best storytellers, the funniest, the kindest, the best-looking, the strongest, and so on – in hopes her child will literally absorb the essence of each. This understanding is found among cultural groups that show no evidence of contact for millennia.
• Children of multiple fathers benefit from having more than one man who takes a special interest in them. Anthropologists have calculated that their chances of surviving childhood are often significantly better than those of children in the same societies with just one recognized father.
• For professional athletes, musicians, and their most enthusiastic female fans, as well as both male and female members of many foraging societies, overlapping, intersecting sexual relationships strengthen group cohesion.
• In the Matis society, extramarital sex appears mandatory.
• Female primates are highly attracted to novelty in mating. Unfamiliar males appear to attract females more than known males with any other characteristic a male might offer (high status, large size, coloration, frequent grooming, etc.)
• Only three percent of mammals can be considered sexually monogamous.
• Adultery has been documented in every ostensibly monogamous human society every studied.
• Among foragers, sharing of resources and sexuality has these benefits: spreads and minimizes risk, assures food won’t be wasted in a world without refrigeration, eliminates the effects of male infertility, promotes the genetic health of individuals, and assures a more secure social environment for children and adults alike.
• Research has demonstrated that the increased sexual receptivity of the female bonobo dramatically reduces male conflict, when compared with other primates whose females are significantly less sexually available. The abundance of sexual opportunity makes it less worthwhile for males to risk injury by fighting over any particular sexual opportunity.
• Anthropologist Thomas Gregor reported eighty-eight ongoing affairs among the thirty-seven adults in the Mehinaku village he studied in Brazil. In the village, extramarital relationships contributed to social cohesion by consolidating relationships between persons of different clans and promoting enduring relationships based on mutual affection.
• Among the !Kung San of Botswana, most girls “marry” several times before they settle into a long-term relationship.
• For the Curripaco of Brazil, marriage is a gradual and undefined process.
• For many societies, virginity is so unimportant there isn’t even a word for the concept in their language.
• A study of sexual behavior among villagers in rural Mozambique found that the 140 men in the study group were involved with 87 women as wives, 252 other women as long-term sexual partners, and 226 additional women on an occasional basis, working out to an average of four ongoing sexual relationships per man (not counting the unreported casual encounters many of these men likely experienced as well).
• Inuit culture had a system of spousal exchange that played an important role in linking families from distant villages in a durable web of certain aid in times of crisis.
• The Kulina of Amazonia have a ritual where the village women “order” the men to go hunting. Before the men return from their hunt, they redistribute the meat they’ve bagged. This ensures that every man returns to the village with meat and is guaranteed of having extra-pair sex.
• The people of the Mosuo region of China have a nearly absolute sexual freedom and autonomy for both men and women. Openly expressed jealousy is considered aggressive in its implied intrusion upon the sacred autonomy of another person, and is thus met with ridicule and shame.
• Societies in which women have lots of autonomy and authority tend to be decidedly male-friendly, relaxed, tolerant, and sexy.
• Among the Siriono of Bolivia, jealousy tends to arise not because one’s spouse has lovers, but because he or she is devoting too much time and energy to those lovers.
• According to E.O. Wilson of Harvard: “all that we can surmise of humankind’s genetic history argues for a more liberal sexual morality, in which sexual practices are to be regarded first as bonding devices and only second as a means for procreation.”
• Prehistoric world population growth is estimated to have been well below .001 percent per year throughout prehistory.
• A study used an MRI machine to examine the brains of women playing an experimental game. The brain responded most energetically to acts of cooperation.
• A review of more than eighty studies of primate behavior found that cooperative and affiliative behavior (like playing and grooming) was ten to twenty times more common than conflict in all primate species.
• The tens of thousands of years before the advent of agriculture was for the most part characterized by robust health, peace between individuals and groups, low levels of chronic stress and high levels of overall satisfaction for most of our ancestors.
• In species with little struggle over females, there is less biological imperative for the males to evolve larger, stronger bodies, so they generally don’t. Men’s bodies are only 10 to 20 percent bigger and heaver than women’s on average, a ration that appears to have held steady for at least several million years. Chimpanzees and bonobos reflect precisely the same range of male/female size difference while enjoying many sexual encounters with many partners.
• Harems are a feature of militaristic, rigidly hierarchical agricultural and pastoral cultures oriented toward rapid population growth, territorial expansion, and accumulation of wealth. Captive harems have never been reported in any immediate-return foraging society.
• If the sperm of more than one male are present in the reproductive tract of an ovulating female, the spermatozoa themselves compete to fertilize the ovum. Females of species that engage in sperm competition typically have various tricks to advertise their fertility, thereby inviting more competitors. Their provocations include sexy vocalizations, scents, or genital swellings.
• Humans, chimps, and bonobos show accelerated evolution of genes involved in sperm and seminal fluid production associated with multiple insemination.
• A man’s sperm production increases significantly when he has not seen his partner for a few days.
• Sexual monogamy permits fertility-reducing mutations to proliferate.
• Research has found that women tend to dress more attractively when they are more likely to be fertile.
• Other studies have found that men prefer women’s bodily smells near ovulation and that women tend to behave more provocatively in various ways when they’re likely to be fertile (they wear more jewelry and perfume, go out more, are more likely to hook up for casual sexual encounters, and are less likely to use condoms with new lovers).
• Because of the complexities of how the two sets of parental DNA interact in fertilization, a man who appears to be of superior mate value (square jaw, symmetrical body, good job) may in fact be a poor genetic match for a particular woman. So, a woman (and ultimately, her child) may benefit from “sampling many males” and letting her body decide whose sperm fertilizes her.
• Women’s orgasms provoke changes in vaginal acidity. These changes appear to assist the sperm cells of the man who provided the orgasm.
• The sexual hunger of the female, and her capacity for copulation completely exceeds that of any male.
• Erotic images elicit significantly quicker and stronger response in women’s brains than either pleasant or frightening images without erotic content.
• Women find classically masculine faces more attractive around ovulation and less masculine faces when not fertile. The birth control pill affects the menstrual cycle and thus may affect a woman’s patterns of attraction. If a woman chooses her partner while she is on the Pill, and then comes off it to have a child, her hormone-driven preferences have changed and she may find she is married to the wrong kind of man.
• Research has found that most women are attracted to the scent of men whose major histocompatibility complex differs from their own. This process is disrupted in women who use birth control pills.
• One study used a fake lie detector and asked college women about their number of sexual partners. Women who thought their answers might be seen reported an average of 2.6 sexual partners. Those who thought their answers were anonymous reported 3.4 partners. Those who thought their lies would b e detected reported an average of 4.4 partners. Women admitted to 70 percent more sexual partners when they thought they couldn’t fib.
• The Muria of central India set up adolescent dormitories where adolescents are free to sleep together, away from concerned parents. The young people are encouraged to experiment with different partners, as it’s considered unwise to become too attached to a single partner at this phase in life.
• A survey of women from twenty-two to fifty-seven years of age found that among those under thirty-five, 61 percent of the women said their primary motivation for sex was emotional rather than physical. Among those over thirty-five, only 38 percent claimed their emotional motivations were stronger than the physical hunger for contact.
• Married men consistently show lower levels of testosterone than single men of the same age. Fathers of young children have even lower levels. Men who are particularly responsive to infants show declines of 30 percent or more right after their child is born. Married men having affairs were shown to have higher testosterone levels than those who weren’t.
• Men with lower levels of testosterone are more than four times as likely to suffer from clinical depression, fatal heart attacks, and cancer when compared to other men their age with higher testosterone levels. They are also more likely to develop Alzheimer’s disease and other forms of dementia, and have a far greater risk of dying from any cause (ranging from 88 to 250 percent higher, depending on the study).
• Key parties originated on military bases, where elite pilots and their wives intermingled sexually with one another.
• Couples with open marriages generally reate their overall satisfaction (with both their relationship and with life in general) significantly higher than those in conventional marriages do.