Sex at Dawn

1. Human sexuality evolved for bonding, not just reproduction

No animal spends more of its allotted time on Earth fussing over sex than Homo sapiens—not even the famously libidinous bonobo.

Social bonding function. Human sexuality evolved primarily as a bonding mechanism to promote social cohesion in small, interdependent bands. Unlike most mammals, humans engage in frequent non-reproductive sex. This served to reduce conflict, strengthen alliances, and blur paternity in prehistoric societies.

Uniquely human traits. Several anatomical and behavioral traits distinguish human sexuality:

• Extended sexual receptivity in females (not limited to ovulation)
• Concealed ovulation
• Large breasts and penises relative to body size
• Face-to-face copulation
• Female orgasm
  These features suggest sex played a broader social role beyond just reproduction in human evolution.

2. Agriculture reshaped human sexual behavior and social structures

Agriculture, one might say, has involved the domestication of the human being as much as of any plant or other animal.

Dramatic shift. The advent of agriculture around 10,000 years ago radically altered human sexual and social arrangements that had existed for hundreds of thousands of years prior. Key changes included:

• Emergence of private property and inheritance
• Shift from egalitarian bands to hierarchical societies
• Increased focus on paternity certainty and sexual control of women
• Development of formal marriage institutions
• Population growth and decreased mobility

Health impacts. The transition to agriculture also negatively impacted human health and lifespan initially:

• Less varied diet led to nutritional deficiencies
• Increased population density facilitated spread of infectious diseases
• More repetitive physical labor caused skeletal problems

3. Female sexuality is more fluid and context-dependent than male sexuality

If you aren't confused already, consider that research psychiatrist Andrey Anokhin and his colleagues found that erotic images elicit significantly quicker and stronger response in women's brains than either pleasant or frightening images without erotic content.

Erotic plasticity. Research shows female sexuality tends to be more responsive to social and cultural influences than male sexuality. Women generally exhibit greater flexibility in sexual preferences and behavior over their lifetimes.

Complex response. Female sexual response involves a more holistic integration of physical and mental factors:

• Genital response often doesn't match subjective arousal
• Arousal to wider range of stimuli than men
• Sexual orientation more likely to shift over time
• Erotic response more affected by relationship context

This complexity and fluidity in female sexuality contrasts with typically more rigid male sexual response patterns.

4. Monogamy is not the natural state for humans

Monogamy is not found in any social, group-living primate except—if the standard narrative is to be believed—us.

Evolutionary mismatch. Humans did not evolve to be sexually monogamous. Evidence against innate monogamy includes:

• Prevalence of adultery across cultures
• Mating systems of closest primate relatives (chimps and bonobos)
• Human anatomical traits suggesting sperm competition
• Existence of non-monogamous societies

Cultural construct. Monogamy and marriage are relatively recent cultural innovations that emerged with agriculture and concepts of private property. They do not reflect our evolutionary heritage.

Alternative arrangements. Throughout history and across cultures, humans have engaged in a variety of sexual and relationship arrangements beyond monogamy, including:

• Polyamory
• Polygyny and polyandry
• "Walking marriages" (as in the Mosuo culture)
• Ritualized extramarital sex

5. Paternity certainty was likely unimportant in prehistoric societies

Far from being shunned as "bastards" or "sons of bitches," children of multiple fathers benefit from having more than one man who takes a special interest in them.

Communal child-rearing. In prehistoric foraging societies, children were likely raised communally rather than by nuclear families. Biological paternity was probably of little importance.

Benefits of uncertainty. Paternity uncertainty may have conferred evolutionary advantages:

• Encouraged male investment in all children
• Reduced infanticide risk
• Promoted group cohesion through shared responsibility
• Increased genetic diversity

Cultural examples. Some contemporary cultures demonstrate beliefs about paternity that differ from Western norms:

• Belief in "partible paternity" (multiple biological fathers) in some Amazonian societies
• Matrilineal inheritance systems
• Cultures where biological fatherhood is considered less important than social fatherhood

6. Human anatomy suggests a history of sperm competition

Adult male humans have the longest, thickest, and most flexible penises of any living primate.

Anatomical evidence. Several features of human reproductive anatomy suggest an evolutionary history of sperm competition (multiple males mating with a female in close succession):

• Large testicles relative to body size (though smaller than chimps)
• Penis shape and thrusting behavior that may displace rival sperm
• Female anatomy that can delay sperm progress to egg

Behavioral support. Other evidence for sperm competition includes:

• Male sexual jealousy and mate-guarding behaviors
• Female copulatory vocalizations that may attract other males
• Patterns of human sexual arousal and fantasy

This evidence contradicts the standard narrative of long-term pair bonding and challenges assumptions about innate monogamy.

7. Prehistoric humans lived in egalitarian, sexually open societies

Foragers divide and distribute meat equitably, breastfeed one another's babies, have little or no privacy from one another, and depend upon each other for survival.

Egalitarian structure. For most of human prehistory, people lived in small, mobile bands characterized by:

• Extensive food and resource sharing
• Lack of significant personal property
• Flexible living arrangements
• Relatively equal status between individuals

Sexual openness. These societies likely featured more relaxed sexual norms:

• Multiple sexual partners over a lifetime
• Less emphasis on sexual exclusivity
• Rituals involving group sexual activity
• Lack of formal marriage institutions

Modern parallels. Some contemporary foraging societies maintain similar egalitarian and sexually open practices, providing insight into prehistoric social arrangements.

8. The standard narrative of human sexuality is deeply flawed

The false expectations we hold about ourselves, each other, and human sexuality do us serious, lasting harm.

Challenging assumptions. The book critiques several common beliefs about human sexuality:

• That humans are naturally monogamous
• That men evolved to seek multiple partners while women seek commitment
• That paternity certainty drove human mating strategies
• That prehistoric life was "nasty, brutish, and short"

Evidence-based revision. Drawing on anthropology, primatology, anatomy, and psychology, the authors propose a new narrative of human sexual evolution emphasizing:

• Importance of social bonding through sex
• Greater sexual egalitarianism in prehistory
• Fluidity and complexity of female sexuality
• Non-reproductive functions of human sexual behavior

9. Sexual jealousy is largely culturally conditioned, not innate

If fear is removed from jealousy, what's left?

Cultural variation. The intensity and expression of sexual jealousy varies widely across cultures, suggesting it is not a fixed biological trait. Some societies show little or no sexual jealousy.

Functional perspective. In many foraging societies, sexual jealousy is discouraged as it threatens group cohesion and cooperation. Instead, these cultures often promote:

• Sharing of sexual partners
• Rituals involving extramarital sex
• Beliefs that minimize the importance of sexual exclusivity

Modern implications. Recognizing the cultural basis of sexual jealousy can help individuals and couples:

• Question automatic jealous responses
• Communicate more openly about desires and boundaries
• Consider alternative relationship structures that may better suit their needs

10. Rethinking relationships can lead to greater fulfillment

Vehement denial, inflexible religious or legislative dictate, and medieval stoning rituals in the desert have all proved powerless against our prehistoric predilections.

Mismatch with instincts. Conventional monogamy often conflicts with evolved human sexual psychology, leading to widespread infidelity, sexual dissatisfaction, and relationship breakdown.

Alternative approaches. Some couples find greater satisfaction through:

• Open relationships or consensual non-monogamy
• Emphasizing emotional intimacy over sexual exclusivity
• Recognizing the fluidity of desire over time
• Communicating openly about sexual needs and fantasies

Cultural shift. Broader social acceptance of diverse relationship models could reduce:

• Shame and secrecy around non-monogamous desires
• Pressure to conform to ill-fitting relationship structures
• Negative judgments of non-traditional arrangements

Ultimately, understanding our evolutionary heritage can inform more realistic and fulfilling approaches to sex and relationships in the modern world.

Last updated: January 22, 2025