Why is Sex Fun?

“Why do humans make love in private, form long-term pair bonds, and have menopause, despite it seeming to defy the logic of reproduction?”

1. Human Sexual Practices Are Unique Among Animals

Humans have a very unusual approach to sex compared to the animal kingdom. Most animals, including our closest relatives like chimpanzees, have sex publicly or only during the female's fertile period. Humans, on the other hand, typically seek privacy for intimacy and do not limit sexual activity to times of fertility.

This behavior extends beyond practicality. Humans often have sex during periods when reproduction is impossible, such as pregnancy or menopause. This practice does not occur in most animals, who conserve their reproductive energy. Additionally, the fact that human females have hidden ovulation—unlike other primates with visible fertility signs—means human males cannot predict when fertilization might occur.

Such practices have puzzled scientists because they seem inefficient and counterproductive from an evolutionary standpoint. However, they serve a broader purpose: fostering deeper bonds between partners, reducing competition for mates, and encouraging cooperative parenting, all of which improve chances of offspring survival.

Examples

• Compare this with baboons, whose females have visible ovulation signs through distinctive physical changes.
• In the animal kingdom, public mating is the norm, seen in lions, wolves, and great apes.
• Concealed ovulation in human females as opposed to visible fertility signals in chimpanzees.

2. Monogamy Protects Offspring and Ensures Survival

Human monogamy is another oddity, as most mammals avoid long-term pair bonding. Humans, however, often form committed relationships with one mate, at least for a significant portion of their lives. This behavior is tied deeply to the survival of offspring.

Child-rearing in humans is a resource-intensive process. Infants are born helpless and require constant caregiving. Pair bonding ensures that both parents contribute to raising their children, a necessity for ensuring the child’s survival, especially in challenging environments.

Evolutionarily, monogamy grew out of the need to guard offspring from threats like predators or lack of food. A stable partnership allows resources to be pooled, the mother to recover, and the father to invest in and protect their shared offspring.

Examples

• Monogamous behavior is rare among mammals; lions and wolves often live in groups, but males don’t usually form exclusive bonds with females.
• Human pair bonding contrasts with chimpanzees, which have a more promiscuous mating system.
• Stable pairings in early human societies likely contributed to collaborative parenting and survival.

3. Recreational Sex Promotes Pair Bonding

While most animals mate strictly for reproduction, humans engage in sex for pleasure and emotional connection. Recreational sex supports monogamy by reinforcing bonds between partners.

The unpredictability of human female ovulation makes it impossible for males to time sexual activity solely to conception. As a result, humans engage in frequent, year-round mating. This pattern strengthens emotional intimacy and encourages males to remain with their partners, rather than seeking out new opportunities to spread their genes.

Sex for connection and pleasure may seem evolutionarily wasteful, yet it improves cooperation between partners. Stronger emotional bonds create a stable environment for raising children and contribute to securing the survival of the next generation.

Examples

• Unlike animals like rabbits, who mate during specific cycles, humans are sexually active year-round.
• Concealed ovulation means males can’t pinpoint female fertility, driving frequent mating attempts.
• Sexual activity in humans often continues during pregnancy, even though no reproduction can occur.

4. Male Contribution to Parenting Is Unique

Most male mammals play little role in directly raising their offspring. Human males, however, frequently help rear children, bringing food and protection to the family unit. This breaks the typical animal pattern, where males focus on mating with as many partners as possible.

Early human fathers contributed significantly through hunting, where meat provided vital nutrition to developing children. This role became a form of sexual selection, as women preferred capable hunters. Over time, this cooperative parenting style strengthened family units and supported offspring survival.

This male involvement evolved as a response to human children’s prolonged dependence on adults compared to apes. Unlike baby chimps, human infants need years of care, making paternal support advantageous.

Examples

• Among Ache Indians, women often choose skillful hunters as partners to ensure food security.
• Wolves display cooperation between parents, much like humans, though this is rare among mammals.
• Human males balance providing resources with defending territory, ensuring family safety.

5. Men Could Theoretically Breastfeed

Though it may sound strange, male mammals, including human males, can lactate under certain conditions. This ability is made possible because mammalian biology already equips both sexes with milk-producing tissue.

While men typically do not produce milk, the stimulation of nipples combined with specific hormonal changes can trigger lactation. Although male lactation could theoretically assist in raising offspring, evolution has not favored it. Instead, men’s physical strength was more advantageous in roles like hunting or territorial defense.

The evolutionary trade-off ensured that human families benefited from complementary parental roles rather than duplicating tasks. While females fed and nurtured, males provided protection and resources, creating a balanced system for survival.

Examples

• Male seahorses carry and give birth to offspring, a reversal of traditional reproductive roles.
• Human males receiving estrogen injections during medical treatments often lactate.
• Historically, humans relied on male strength for hunting and guarding more than infant care.

6. Menopause Is an Evolutionary Quirk with Purpose

In the animal world, most females remain fertile until death—making human menopause unusual. Menopause stops fertility midlife, which initially seems counterintuitive to passing on genes. However, it provides long-term benefits.

By ceasing reproduction, women shift their focus to raising existing children and assisting their grandchildren. Older women play vital roles by transferring knowledge and helping their descendants thrive. This grandparental investment ensures that their lineage survives, balanced with their own longevity and health.

The longevity afforded by menopause allows women to stay healthy, avoid risky childbirth later in life, and care for multiple generations—an advantage in early human communities.

Examples

• Great apes rarely live beyond 60, while humans may reach over 100 with menopause aiding longevity.
• Prehistoric societies benefited from postmenopausal women as custodians of oral traditions.
• Rationing fertility reduces risks of late-pregnancy complications in modern women.

7. Sexual Signals Advertise Genetic Fitness

Humans, like many animals, use physical traits to signal reproductive health and genetic quality. Features such as muscle tone, body fat, and facial symmetry communicate qualities that potential mates find attractive.

These signals, akin to a peacock’s tail, may seem biologically costly but ultimately aid in mate selection. Larger muscles in males historically indicated capability for resource collection and protection. For women, features like certain fat distribution hinted at fertility and the ability to nourish offspring.

These signals are deeply ingrained, influencing what humans find appealing. Although modern societal pressures influence preferences, they are rooted in old evolutionary needs.

Examples

• Peacocks’ tails demonstrate genetic fitness despite the energy cost involved.
• Men’s muscular builds once signaled their ability to provide food or defend family groups.
• Women’s physical traits like hip-to-waist ratio correlate with fertility and health.

8. Privacy in Sex Emerged for Evolutionary Benefits

Most animals mate openly, while humans seek privacy. This behavior may have evolved to reduce conflicts, build trust, and create exclusivity within partnerships. By ensuring privacy, couples reinforce bonds, guarding against jealousy and competition.

This shift fosters cooperative parenting by bolstering loyalty and mutual respect, necessary for raising dependent children. Privacy brings more stability and long-term partnering.

Examples

• Chimpanzees’ public sexual behavior contrasts sharply with human habits.
• Early human couples likely relied on intimacy to strengthen their survival partnerships.
• Privacy helps lessen tensions within social groups by hiding sexual activity.

9. Hidden Ovulation Encourages Pair Stability

Unlike most animals with obvious fertility signals, human females evolved concealed ovulation. This unpredictability keeps males engaged, strengthening long-term pair bonds.

Hidden ovulation removes direct competition over fertile females. Instead, it encourages sustained relationships, ensuring support during pregnancy and childrearing. This trait likely shaped human reproductive behavior into the cooperative, pair-based system we see today.

Examples

• Baboons display fertility signals through swollen, reddened skin.
• Concealed ovulation ensures consistent attention from male partners year-round.
• Early humans evolved this advantage to maintain supportive male presence in families.

Takeaways

1. Practice open communication and cooperation with a partner to foster stronger bonds during challenging times.
2. Recognize the evolutionary basis of your physical and emotional preferences in relationships to better understand yourself and others.
3. Support elder family members as their role in passing down knowledge is evolutionarily and culturally essential.