Sex at Dawn by Christopher Ryan and Cacilda Jetha


Read it. Just.. read it. My top recommendation.

This book calls into question many assumptions about human behavior. This is a list of topics discussed in this book;

  • sex (freaking duh)
  • infidelity
  • the female libido
  • female copulatory vocalizations
  • relationships
  • jealously
  • suicide
  • war
  • anger
  • genital design
  • other cultures practices of sex
  • the fallacy of universal human monogamy
  • testosterone levels
  • masturbation
  • pornography
  • the shift from foraging to agriculture
  • disease
  • BONOBOS (I had never heard of bonobos, like many other people I thought, “Yup, chimpanzees, that’s the closest thing to us.”)
  • sperm competition vs. alpha male
  • gender inequality
  • famine

Like, it was one of the most jaw-dropping things I’ve ever read. I wanted to walk around and ask people, “Do you know about this?”. Talking about this book makes me want to throw up, not because I’m disgusted, but because it just too much incredible insight to handle.

It reminds me of criminal investigation, where you thought all the facts were upfront. Everything was straightforward. It had been explained. It was time to move on. Then the defense calls a witness who was overlooked. Suddenly, everything you thought you know about the case starts to come crashing down and a new narrative emerges exonerating the defendant (who you thought was undeniable guilty earlier). It is sensational.

“With the earliest evidence of agriculture dating to bout 8000 BCE, the amount of time our species ha spent living in settled agricultural societies represents just 5 percent of our collective experience, at most. As recently as a few hundred years ago, most of the planet was still occupied by foragers…Several types of evidence suggest our pre-agricultural (prehistoric) ancestors lived in groups where most mature individuals would have had several ongoing sexual relationships at any given time. Though often casual, these relationships were not random or meaningless. Quite the opposite: they reinforced crucial social ties holding these highly interdependent communities together.”

“The human male has testicles far larger than any monogamous primate would ever need, hanging vulnerably outside the body where cooler temperatures help preserve standby sperm cells for multiple ejaculations. He also sports the longest thickest penis found on any primate on the planet, well as an embarrassing tendency to orgasm too quickly. Women’s pendulous breasts (utterly unnecessary for breastfeeding children), impossible to ignore cries of delight (female copulatory vocalization), and capacity for orgasm after orgasm all support this vision of prehistoric promiscuity.”
Farming was biggest shift in human life
Differ from chimps and bonobos by roughly 1.6% DNA
Fallacy that the female libido is weak, is this true? Some studies try to confirm but more could be there
Not that prehistory females had sex with strangers all the time but that multiple partners could have been common
Female ovulation, why hidden? Maybe to keep a male around or confuse male as to who’s child she was carrying.
How does a male know the female that he is monogamous with was faithful or that the child is his
Gibbons are very dissimilar to humans in social behavior and genetics.
“The chimpanzee resolves sexual issues with power; the bonobo resolves power issues with sex.”
The shift from foraging to farming is hypothesized, based on skeletal remains, to show increases in famine, vitamin deficiency, violence, reduction in lifespan. Less of a radical leap forward and more of a fall from grace.
Sex for pleasure is very much a uniquely human thing. Sex strictly for reproductive purposes is more animalistic. Example used is a horny monkey is acting more human than a man or woman only having sex once or twice a year.
“As beckerman and valentine explain, “it is difficult to come to any conclusion except that particle paternity is an ancient folk belief capable of supporting effective families, families that provide satisfactory paternal care of children and manage the successful rearing of children to adulthood.”
 soccer tribe, a researcher followed a soccer team around to observe their closeness. Humor was used to deflate egos, and it was observed that if one of them scored—sexually—he was not possessive but almost too happy to see his teammate succeed with the same girl. Lack of jealousy was measure to which selfishness was suppressed off and on field.
Franz de Waal could have been referring to any of the previous Amazonian tribes mentioned when he states that the male has no idea which copulations resulted in his child or not. However, he was writing of the bonobo.
“No creature needs to be threatened with death to act in accord with its own nature.”
Standard narrative assumptions
  • A prehistoric mother and child needed the meat and protection a man would provide
  • A woman would have had to offer her own sexual autonomy in exchange, this assuring him that it was his child he was supporting


After centuries of barbaric punishments for adultery persists and persists. No group living nonhuman primate is monogamous, adultery has been documented in every human culture studied. How does it come naturally? Why would we risk so much for something that runs against human nature. If monogamy was natural and standard these enforcements would be unnecessary

People pair off for days, hours, or years. Some anthologists may say this mean that marriage is universal, or use the word pair bond to describe it. English language cannot fully describe the human experience.

The Mosuo- debunk the idea of only patriarchy, as do the minangkabau of West Sumatra. Also remember Mosuo flower rooms and the group paternity
Penguins, swans, prairie voles are all not monogamous.
Marriage, mating, or love are socially constructive phenomenon. Rampant ritualized group sex, mate swapping, unrestrained casual affairs, and socially sanctioned sequential sex all happened in cultures where anthropologists claimed marriage exists and are monogamous.
“For most human beings reality is pretty much what we are told it is. Like practically everything else, jealousy reflects social modification and can clearly be reduced to little more than a mirror irritant if consensus deems it so.”
If fear is removed from jealously, what is left?
Among foragers where property is shared poverty seems to be a nonissue. In Stone Age Economics, Marshal Sallins explains the world’s most primitive people do not have that many possessions but they are not poor. Poverty is a social status and the invention of civilization.
The prisoners dilemma fallacy conclusion. Players who played longer chose to stay quiet, female MRI found that the brain reacted stronger to cooperation than betrayal.
Prehistoric humans could not store food, but that does not mean they lived in hunger. Harris lines in bones, and lines in teeth, marking nutrition and growth, see healthier lines in forager remains then cultures that relied on cultivation.
A foragers diet has a variety of nutrients. Crickets can be collected very efficiently in an hour. “Stone age populations lived healthier lives than did most of the people who came immediately after them.”
Many key studies are flawed by context. Goodall made food zero sum game with bananas.
The Yanomami guy brought division and instigated violence.
Chimps spread out and will even alert others to food sources. Selfish?
Many diseases can be traced to domesticated animals or are reliant on high density populations.
Gorillas are huge, with a a tiny penis, and small testes inside body vs. bonobos that may be 100 lbs have a penis 3x the size of a gorillas and testes the size of chicken eggs on the outside of the body.
With bonobos the competition takes place on the microscopic level with sperm. Everyone gets some and fight happens ‘inside’ instead of ‘outside’.
semen displacement, it is hypothesized that the penis is designed to displace semen left by other males from the vagina
Researchers and studies showing
  • men who ejaculated more than 5 times per week between 20-50 were less likely to develop prostate cancer later in life.
  • Daily ejaculation dramatically reduced damage to DNA cells increasing fertility
  • Frequent orgasm is shown to correlate with reduction in heart disease chances

Male reproductive approach


Women used to be treated for hysteria by having a physician get them off or nurse. Many of the symptoms matched sexual frustration today. 1600s-1920s
The vibrator was the 5th electrical appliance patented for use. 1902
Recent researchers suggest that women who do not use condoms during sex show decreased sign of depression.
Regardless of sexual orientation women’s genitals reacted to any visual stimuli of sex although they reported only be aroused by heterosexual human sex.
Does the pill affect a woman’s hormone driver preferences for a male? “The Sweaty T-Shirt Experiment” study and smell attraction. MHC complex was different than their own, needing broader immune defense system. When on pill, they chose MHC similar to their own.
Suicide and Testosterone
Massive conflict to what society dictates and what our biology demands. When boys become of age their bodies are all about SEX NOW but it is encouraged that that energy is used for something else. Testosterone levels correlate to likelihood a young man/woman getting into trouble. In U.S, adolescent males are five times more likely to kill themselves than females. Among Americans between 15-35 suicide is the third leading cause of death. Teenage boys kills themselves at a rate of double than any other social group.
Deprivation of the body pleasure throughout life, particularly through formative years of infancy & adolescence is closely related to amount of warfare and culture violence in societies.
Mens testosterone levels recede over time, monogamy drains testosterone. Novel sexual partner can increase testosterone but it can be viewed of by love from the males point of view.
Talk to testosterone
A brief chat with an attractive women can raise testosterone levels by 14%, when these same men talked to other men there testosterone levels fell by 2%
Men with lower levels of testosterone are more than 4 times as likely to suffer from depression, heart attacks, and cancer when compared with other men their age with higher levels of testosterone. Also more likely to develop dementia and have a greater risk of dying from any cause.

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