Why is sex fun? This question has intrigued scientists for years. Sexual pleasure isn’t just about biology—it’s also a big part of human relationships and culture. While sex originally evolved for reproduction, in humans it serves other purposes like bonding, emotional connection, and even stress relief. In this article, we’ll look at biological, psychological, and cultural reasons why sex is enjoyable, using ideas from Jared Diamond’s book Why Is Sex Fun? The Evolution of Human Sexuality.
Concealed Ovulation and Recreational Sex
One unique feature of human sexuality is concealed ovulation. Unlike many animals, women don’t show obvious signs of fertility. This means sex can happen anytime during the menstrual cycle, not just when a woman is fertile. Diamond offers two main theories for why this evolved:
Many-Fathers Theory: Women had sex with multiple men to confuse paternity, which reduced the risk of infanticide.
Daddy-at-Home Theory: Frequent sex encouraged men to stick around, provide resources, and protect their children.
These ideas help explain why sex became recreational and pleasurable instead of only for reproduction.
Pair Bonding and Long-Term Relationships
Humans often form long-term partnerships, like marriage, which is rare among mammals. These bonds help with raising kids and cooperating in social groups. Sexual pleasure strengthens these relationships, making them more stable. Diamond points out that this is very different from most mammals, where males usually don’t help care for offspring.
Private Sexual Behavior
Humans also tend to have sex in private, unlike most animals. Diamond suggests this evolved because of social norms and the need to keep peace in groups. Privacy reduces jealousy and conflict, making sex less disruptive to social life.
Menopause and Its Role
Menopause seems strange from an evolutionary perspective—why stop reproducing while still healthy? Diamond argues it’s a trade-off: older women focus on caring for children and grandchildren instead of risking late pregnancies. This helps families survive and pass on knowledge.
Secondary Sexual Characteristics
Human bodies show traits that signal health and fertility, like breasts, hips, and muscles. Diamond explains theories behind these traits:
Runaway Selection: Preferences make traits more exaggerated over time.
Handicap Principle: Costly traits show genetic quality.
Truth-in-Advertising: Traits honestly signal health and fertility.
For example, fat in breasts and hips may signal ability to nurse and a wider birth canal, while muscles suggest strength and resourcefulness.
Summary
Diamond addresses aspects of human sexuality such as why women's ovulation is not overtly advertised; why humans have sex in private rather than in public like other mammals; and why the ovaries are U-shaped.[1]
Why Is Sex Fun? received a positive review from the biologist Steve Jones in The New York Review of Books. Jones described the book as engaging and interesting. However, he questioned Diamond's treatment of concealed ovulation, finding it inconclusive.[3]
The anthropologist Peter B. Gray and the evolutionary biologist Justin R. Garcia maintained that Why Is Sex Fun? was one of the best-read books on human sexuality. However, they considered it "informative but too thin in substance".[4]
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