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Sex At Dawn Book Summary and Analysis | Christopher Ryan and Cacilda Jethá

Life gets busy. Has Sex At Dawn been gathering dust on your bookshelf? Instead, pick up the key ideas now.

We’re scratching the surface here. If you don’t already have the book, order the book or get the audiobook for free to learn the juicy details.


Sex at Dawn caused a stir in 2010 upon its release, with groundbreaking views that challenged the status quo. Sex columnist Dan Savage called it the most important book since Kinsey. However, famous cognitive psychologist Steven Pinker called it a work of pseudoscience. 

Focusing on monogamy evolution in humans, Christopher Ryan and Cacilda Jethá argue that monogamy is a modern thing. Historically, it would have been common for people to have had multiple sexual partners, which would have been considered acceptable. The book bases its arguments around the idea that pre-agriculture we lived in self-contained groups of hunter-gatherers. Then, agriculture led to higher population density and greater jealousy and social inequality. These groups would have been small communities consisting of between 15 and 30 people.


About Christopher Ryan and Cacilda Jethá

A husband and wife, Christopher Ryan and Cacilda Jethá, have their background in psychology and psychiatry, respectively. 

Christopher Ryan is an American author who wrote his doctoral dissertation on the prehistoric roots of human sexuality. This dissertation, guided by the humanistic psychologist Stanley Krippner, set the foundations for Sex at Dawn. Since then, Ryan has contributed to Psychology Today, hosted a popular podcast called Tangentially Speaking, and given a TED talk called Are we designed to be sexual omnivores?

Cacilda Jethá is a practicing psychiatrist, born in Mozambique, who specializes in psycho-sexual disorders and couples therapy. She has completed field research on sexuality for the World Health Organisation and co-authors a blog, with Christopher, for Psychology Today.

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Where It All Began

“Rather than a plausible explanation for how we got to be the way we are, the standard narrative is exposed as contemporary moralistic bias packaged to look like science and then projected upon the distant screen of prehistory, rationalizing the present while obscuring the past. Yabba dabba doo.”

– Christopher Ryan

Our Biases Limit Our Understanding of Sexual Relationships From the Past

The book begins with the authors considering our evolutionary lineage and how our sexual relationships and mating systems differed historically. The book explains how both researchers and the wider public are guilty of “Flintstonization,” where they apply modern ideas and constructs onto societies of the past. This modernism has led the majority of people to assume that our species is, always has been, and always will be predominantly monogamous. 

The Reality of Sexual Relationships in the Past

The authors explain that before the development of agriculture, we lived in egalitarian, hunter-gatherer groups. Within these groups, sexual interaction would have been viewed in the same way as all other resources, such as childcare, food, and protection. During this time, the idea of pair-bonding through marriage, monogamous relationships, and nuclear family was non-existent. These are constructs that have emerged after the development of agricultural practices and the modernization of civilizations. 

Here are just some of the examples given by the authors that are suggestive of us having had a non-monogamous history:

  • Human sexual dimorphism
  • Female copulatory vocalization
  • Testicle size
  • Our modern appetite for sexual novelty

Modern Hunter-Forager Groups Can Inform Our Understanding of Our Old Hunter-Forager Practices

The authors explain how certain behaviors exist within modern hunter-forager groups that are in-line with expectations of our historic sexual practices. Firstly, male selection was not subject to intragroup competition; this is because sex was not scarce. Instead, the thing that was commodified during this time was sperm. Sperm was more critical during this time, in terms of paternity factors than sexual selection. Within modern hunter-forager groups, this is called partible paternity.

Our Closest Evolutionary Ancestors Are Not Monogamous

“Sex for pleasure with various partners is, therefore, more “human” than animal. Strictly reproductive, once-in-a-blue-moon sex is more “animal” than human. In other words, an excessively horny monkey is acting “human,” while a man or woman uninterested in sex more than once or twice a year would be, strictly speaking, “acting like an animal.”

– Christopher Ryan

The authors use the example of social primates, our closest evolutionary relatives, as evidence that we are not naturally monogamous beings. We share up to 98.4% of our DNA with Chimpanzees and Bonobos. They point out that monogamy is not found in any social group primate apart from humans. Many social behaviors that we see in humans are also found in our closest relatives, yet monogamy seems to be a purely human construct. And, according to the authors, a strictly modern human construct. For example, Bonobos are not patriarchal but matriarchal. Resources are shared much more evenly, and the females keep their influence through kindness and affection, forming bonds with other males and females.

Additionally, Bonobos will frequently have sex with other males and males to resolve conflicts, but also as a way of greeting someone. Sex is not about reproduction or resources. An interesting comparison to be made with humans is that the Bonobos are the only other animal in the animal kingdom who have sex facing each other. Plus, both Bonobos and humans have sex far more frequently than other animals; both have sex thousands of times per birth. Both Bonobos and humans have sex when the female is not ovulating, also. Similar examples are shown in dolphins and suggest that our natural sexual tendencies might be more aligned with the other non-monogamous social animals. 

The authors state that, like primates, our prehistoric ancestors utilized sex as a currency, a buffering mechanism, and a way of keeping the group on an even keel. It is possible to maintain monogamy, but it is not our natural tendency. There is a reason we all possess a sex drive that isn’t fixed to just one mate and why people often fail to maintain a monogamous relationship. Even if people maintain their faithfulness throughout a relationship, it is still something they have to work for rather than being their natural tendency. 

A Summary of Our Modern Narrative and Why It Doesn’t Stack up

Summary of Our Modern Narrative

The standard modern understanding of sexual relationships is that males and females are obsessed with mating value based on reproductive capabilities. 

This means that males search for:

  • Youth and fertility
  • Absence of prior sexual experience
  • Likelihood of infidelity

Comparatively, females search for:

  • Signs of wealth
  • Prospects of future wealth
  • Physical health
  • Social status
  • A high likelihood that her mate will stay to protect and provide for the children

Provided those searching feel both parties meet the above criteria, then they mate and establish a monogamous bond. Unfaithfulness is a possibility after this, though. The females watch for signs that he is considering being unfaithful, while they also look for opportunities for sexual reproduction with other genetically superior men around their time of ovulation. The males also watch for signs of sexual infidelity but are mainly interested in taking advantage of sexual opportunities with other women. The reasoning behind these differences is that sperm is relatively unlimited, while eggs are limited. 

Why It Doesn’t Stack Up

Although the authors accept that these are generally accepted things in the modern world, the authors believe that these are symptoms of the environment rather than things hard-wired into us as humans. These current behaviors are driven by the accumulation of private property and power. Ownership pushed humans towards more selfish actions, something that the authors believe is at odds with our natural tendencies. These selfish behaviors were characterized by monogamy and marriage. Although attraction played a part, the most important reasons for monogamy were for status and control of the possessions that were now private property. Since the men did all the farming, the women lost their gatherer jobs and were now stuck taking care of the children. It now became important for men to know “the children they own,” to pass on the prosperous life they had built to them. The only way to ensure this was to publicly scrutinize women who had sex with different partners and marriage.

On top of this, as hunter-gatherers, we would have moved from area to area; therefore, it was unlikely that long-term relationships could develop. The development of agriculture meant roaming was needed less, and long-term monogamous relationships could also develop.

The Push Towards Ownership Repressed Women’s Natural Sexual Drive

“Before the war on drugs, the war on terror, or the war on cancer, there was a war on female sexual desire. It’s a war that has been raging far longer than any other, and its victims number well into the billions by now. Like the others, it’s a war that can never be won, as the declared enemy is a force of nature. We may as well declare war on the cycles of the moon.”

– Christopher Ryan

As previously stated, the authors highlighted that as private ownership became commonplace, men found ways to prevent women from having sex with different partners. One of these, public scrutiny, has ultimately led to women’s sexual pleasure being stigmatized for centuries. Simultaneous with the creation of marriage and the idea of a family, the idea that women’s libido is lower than men’s was introduced. The authors point out that this is ultimately wrong. Both men and women, on average, have equal libidos. 

How Agriculture Screwed up Our Diet and Sex Life

The authors also argue that this transition was ultimately hurtful to our diet and our sex lives. Previously we would eat whatever we found that was edible; this meant that we had a wide variety of foods and nutrients. The mass production of one thing, encouraged by agriculture’s development, took a massive toll on our health. 

Henceforth, the authors state that roughly 10,000 years ago, humans developed agricultural practices that influenced the environment and pushed us toward modern, monogamic behaviors. These behaviors are described as modern because 10,000 years is a short time when we consider how long Homo Sapiens have existed. The most recent estimates believe that Homo Sapiens have existed for 200,000 years. Therefore, this would suggest that we have spent most of our species’ existence in non-monogamous societies, with only approximately 6% spent in monogamous societies. Importantly, too, this is too short a time for us to have changed evolutionarily towards being naturally driven to adopt monogamy. 

Humans Are Naturally Egalitarian and Selfless

“When you can’t block people’s access to food and shelter, and you can’t stop them from leaving, how can you control them? The ubiquitous political egalitarianism of foraging people is rooted in this simple reality.”

– Christopher Ryan

The typical characteristic associated with humans is selfishness, tied to the idea of survival of the fittest. However, the survival of the fittest does not always mean the fittest individual wins but that the fittest group wins, whether that is an individual or a combination of individuals. The authors argue that humans are more selfless and egalitarian than we give ourselves credit. Often sharing is the most evolutionary adaptive approach for humans, as it distributes the risk of decisions among a group of individuals rather than on one individual. 

How Our Bodies Are Adapted to Having Multiple Sexual Partners

The authors explained multiple ways in which our bodies are evolved to have multiple sexual partners, rather than just one. These are some of them.

  1. A man’s testicles are stored outside of the body. The reason for this is that the sperm is kept at an optimum temperature
  2. The shape of the penis is for high sperm precision
  3. Women moaning loudly might be a call to attract further men
  4. Women take longer to orgasm and can have sex for longer, as this maximizes potential partners

Concluding Points 

The authors conclude that monogamy can work, but it isn’t the only option. They conclude that the least we can do is be honest about our lineage and challenge the prevailing view that we are naturally a monogamous being. Instead, likely, monogamy is not our natural tendency, but it might be the most adaptive approach for some in the modern world. 

Related Book Summaries

Mating In Captivity

The Truth

The Seven Principles for Making Marriage Work

Men Are From Mars, Women Are From Venus

Modern Romance

The Way of The Superior Man

Difficult Conversations

How to Think More About Sex


No More Mr Nice Guy

The 5 Love Languages

The Art of Seduction


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