Sex at Dawn: How We Mate, Why We Stray & What It Means for Modern Relationships

Sex at Dawn: The Prehistoric Origins of Modern Sexuality
Category: Relationships
Genre: Self-Help
Publisher: Harper Perennial
Published: 7/5/2011
A controversial, idea-driven book that challenges everything you (think you) know about sex, monogamy, marriage, and family. In the words of Steve Taylor (The Fall, Waking From Sleep), Sex at Dawn is “a wonderfully provocative and well-written book which completely re-evaluates human sexual behavior and gets to the root of many of our social and psychological ills.”

Book Summary - Sex at Dawn: The Prehistoric Origins of Modern Sexuality by Christopher Ryan and Cacilda Jetha

Key Insights

From an early age, many of us are told that we will one day fall in love and marry a suitor who is our complement in every way. Why is it, then, that even with the echoes of this moral obligation ringing in our ears, do we, as a species, so often feel inclined to search for something more in the form of an affair? Why is monogamy the prevailing point of view when humans have an innate tendency to deviate from its rigid structure? And now, with more marriages failing than ever before, ‘hook-up’ culture running rampant, and definitions of sexuality continuing to evolve, what is the future of sex in our world? And how did we get here from where we started out centuries ago?

Key Points

Casual Sex

What’s your number? Yes, you know the number I’m talking about.

Sex partners.

Whatever your answer, chances are, it is much lower than the score of many of your hunter-gatherer predecessors, who led highly promiscuous lives and viewed casual sex as the norm.

In fact, sex was so commonplace in prehistoric times that it was often considered a community resource akin to food, shelter, and childcare. It was considered to be an effective process for keeping people cooperative and relaxed within their communities.

So, what changed?

With the rise of agriculture, cultures, and religions around the world began penalizing promiscuity through strict codes of conduct. Still--like the Romans who customarily allowed a bride to take part in an orgy before her wedding--some traditions that allowed for a suspension of the rules of monogamy continued to exist.

Shared Fatherhood

In the world today, if a man has fathered more than, say, 12 children, it is considered a bit of a taboo. In prehistoric times, this was definitely not the attitude that prevailed.

In fact, because childcare was considered a group responsibility, it did not necessarily matter who a child’s parents were. Instead, the group as a whole worked to keep offspring fed and sheltered.

In some South American tribes, this collectivist attitude towards parenting and sex continues to reign supreme. For instance, in the Ache tribe, each child has four types of fathers:


  • The one who ‘put it in’
  • The one who ‘mixed it’
  • The one who ‘spilled it out’
  • The one who supplied the child’s ‘essence’


In this culture, women are encouraged to have sex and collect semen from multiple men. Ache women also engage in sex with other women. Ache men involve themselves in same-sex pairings as well.

The Invention of Agriculture

While there are arguably many positive outcomes that came as a result of advancements in agriculture, scientists today believe that cultivating plants and domesticating animals on a large scale ultimately caused significant damage to our social and sexual lives.


Along with agricultural innovation came the trio of evil: possessiveness, jealousy, and greed.

While hunter-gatherers had previously shared resources collectively, because they were on the move and nobody could travel with large amounts of anything, the rise of farming ushered in an era of sedentary living accompanied by competitive ownership and prosperity.

Soon, a chasm developed between the rich and the poor, which would lead to widespread issues of hunger and war not long after.

Women, in particular, were harmed by the new societal tendency towards possessiveness. It had become commonplace for men to force women into fidelity by way of physical force, public shaming, or law...such as marriage.

Plus, while the men farmed, women began taking care of the children on their own. This gave rise to the idea that women are intended to be in the home while men are working out in the field. Around this time, there was also a belief that women had weaker libidos than men.

Sexual Hunger in Women

Based on the outdated belief that women have weaker libidos than men, a recent study was conducted and found that the opposite is actually true. If anything, women’s libidos are stronger than those of men.

In this study, a group of men and women--both hetero and homosexual--were shown erotic films and asked to indicate their arrousal levels as they watched. At the same time, electrodes were also measuring participants’ blood flow to see how physically excited they became.

So, if women are just as likely to be aroused as men (if not more), how did the stereotype of women wanting sex less frequently than their male counterparts originate?

Social pressure.

Historically, women were (and still are) made to feel that their sexual pleasure is less consequential than men. For this reason, many women adjusted their behavior in this realm during the agriculture boom, not on the basis of their true desires so much as in response to perceived expectations.

The same study also indicated that sexual fluidity is much more common in women than in men, as women are attracted to a larger variety of stimuli. And yet, women are far more readily able to suppress their sexual feelings than men.

Primate Relatives

After this next bit, you will never experience a trip to your local zoo the same way again.



While we, as humans, share close ancestry with a variety of primates, the DNA of bonobos and chimps only differs from ours by a margin of 1.6 percent. For this reason, when we have questions about human behavior, it is logical to look to our closest relatives for answers: bonobos and chimps.

Bonobos and chimps are highly sexual creatures, particularly the females, who are known to have sex with many males in rapid succession. They also experience oral sex, kissing, and orgasms.

Much like prehistoric humans, bonobos share sex within their communities. Some scientists believe that this primate behavior is indicative that monogamy is not a natural state for humans.

Competitive Mating System

Why do penises look the way they do? There is actually a biological reason for their size and shape. The shape of the human penis is such that in doing the thrusting motion, a man can pump out the semen of the men who came before him (literally). The first spurt of semen that comes from a man contains chemicals that can protect his sperm from the sperm of his predecessors.

Furthermore, male testes have evolved to be large (both in humans and primates), because the bigger they are, the more equipped they are to hold a significant amount of sperm cells at an ideal temperature. Plus, sizable testes create a competitive advantage--the more substantial the testes, the more sperm cells per ejaculate which create a greater likelihood of impregnation.

Remnants of Our Past

While the human species has moved away from the promiscuity of our ancestors in many regards, remnants of our predecessors’ proclivities are evident to this day.

For instance, why are some people loud during sex?

Historically, women were intentionally loud when engaging in sexual activity, because they were signaling to other men that they were having sex, and essentially saying, “Hey, you should be having sex too!”

Another remnant of our ancestral past is with regard to orgasm. Women often take longer to reach climax than men and they can also have multiple orgasms in some cases. Evolutionarily, this occurs so that women are able to have sex with men one after another in succession! Men, get in line!

The ‘break’ that a man needs after having an orgasm is evolutionary as well. Historians believe that this refractory period used to be a time during which other men could come and try their luck at impregnating a woman.

In prehistoric times, attaining the outcome of pregnancy seemed to be more important than the specific sexual actions it took to get there.

True Love

Loving someone does not necessarily mean that you will want to have sex with them forever. In fact, we, as humans, are biologically programmed to seek out sexual encounters with multiple partners throughout the course of our lives.

However, we are surrounded by romantic comedies and real-life examples of monogamy and that ideology alone.

Monogamy, in and of itself, is actually bad for your health. After all, when men are in long-term relationships, they often experience a large drop in testosterone levels over time. This can lead to serious conditions such as depression, heart disease, and cancer.

The Main Take-away

In order to move the needle forward on our conversations about monogamy and infidelity, we must be willing to discuss our true desires, even if they feel socially taboo. The more open we can be in sharing our personal stories, the more likely we are to bridge the gap between our culture’s promotion of monogamy and our biological belief in sex with multiple partners. Do not immediately write off the possibility of sexual inclusivity within a nuclear family household.

Additionally, rather than shying away from discussing sexuality with our children, we must engage adolescents in these complex, multi-faceted topics.

About the Author

Christopher Ryan, co-author of Sex at Dawn: The Prehistoric Origins of Modern Sexuality, is married to the book’s other author, Calcilda Jetha.

Prior to publishing his debut text, Ryan attended Saybrook University in San Francisco, California where he completed a Ph.D in psychology. Ryan’s doctoral thesis focused on the prehistoric roots of human sexuality, which ultimately became the basis of his writing.

Currently, Ryan hosts a popular podcast called Tangentially Speaking, which aims to inspire individuals to take stewardship of the planet.

Calcilda Jetha, co-author of Sex at Dawn: The Prehistoric Origins of Modern Sexuality and long-time spouse of Christopher Ryan, is a practicing psychiatrist with a focus in couples therapy and psychosexual disorders.

Jetha, who was born in Mozambique and fled with her family to Portugal amidst civil war, has conducted extensive research for the World Health Organization (W.H.O). Specifically, she studied sexual behaviors among rural Africans in order to help develop AIDS-preventions efforts for this population.

Calcilda Jetha and Christopher Ryan currently reside in Barcelona, Spain.


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