Why Is Sex Fun?

Why Is Sex Fun? The Evolution of Human Sexuality

Company type	Book
Industry	Publishing
Founded	1997
Founder	Jared Diamond
Products	Non-fiction book on human sexuality and evolutionary biology

Why Is Sex Enjoyable? The Development of Human Sexual Behavior is a 1997 publication by biologist Jared Diamond that delves into the origins and characteristics of human sexuality.

Summary

Diamond investigates the distinctive features of human sexual behavior, such as hidden ovulation, private sexual interactions, and the U-shaped configuration of ovaries. The book is divided into seven chapters:

1. The Animal With the Strangest Sexual Habits: Diamond underscores what makes human sexuality unique:
   1. Unlike many animals that engage in solitary mating, most men and women establish long-term pair bonds ("marriage") with exclusive sexual partnerships.
   2. Joint parental care is a hallmark of marriage, differing from the majority of mammals where females solely nurture offspring.
   3. Human couples reside within social groups instead of defending exclusive territories.
   4. Sexual encounters generally take place away from public view.
   5. Concealed ovulation results in sex primarily serving recreational purposes, a rarity among mammals except for species such as bonobos and dolphins.
   6. Women undergo menopause, ending fertility typically around their forties or fifties.
2. The Conflict Between the Sexes: Male and female reproductive goals frequently diverge, shaped by:
   1. Parental investment: Females invest heavily due to the demands of producing eggs, pregnancy, and breastfeeding.
   2. Child-rearing responsibilities restrict women's reproductive frequency; men face fewer biological limits but often invest because infants require protection.
   3. Certainty about parenthood varies; women have assured maternity, whereas men historically lacked paternity certainty before the advent of DNA testing.
3. Why Are Men Not Lactating?: Although men have the physiological capacity for lactation, evolutionary pressures have not favored male breastfeeding; however, this could potentially change in the future.
4. Inopportune Timing for Love (Recreational Sex): Humans engage in recreational sex despite inherent risks. Two hypotheses offer explanations:
   1. The "Many-fathers" hypothesis posits that concealed ovulation creates paternity uncertainty, thereby lowering the chance of infanticide.
   2. The "Daddy-at-home" hypothesis suggests that frequent sexual activity promotes male provisioning and protection.

Together, these theories imply that concealed ovulation evolved within a promiscuous context to prevent infanticide and later supported monogamous relationships with reliable males.

1. What Role Do Men Play?: Research on communities in New Guinea and Paraguay challenges assumptions about men's childcare involvement. Men primarily contribute through protection—mainly from other males—and food provision. Nonetheless, women often supply more calories through gathering activities. Men fall into two categories: "providers," who consistently supply food, and "show-offs," who hunt large game but frequently fail; providers tend to offer greater benefits to their families despite show-offs enjoying higher social prestige.
2. Increasing Reproductive Success by Having Fewer Children (Menopause): From an evolutionary standpoint, menopause is perplexing. Diamond proposes it reflects a strategic shift where older women focus on enhancing the survival chances of existing children and grandchildren rather than producing new offspring. Moreover, elders play crucial roles by sharing knowledge within traditional societies.
3. Honest Signals (Secondary Sexual Characteristics): Various theories address secondary sexual features:
   1. Fisher's runaway selection theory suggests traits favored by females become exaggerated beyond survival advantage until natural selection intervenes.
   2. Zahavi's handicap theory argues that traits which impose costs nonetheless serve as honest indicators of fitness; examples include peacock tails and human status symbols like clothing or automobiles.
   3. The truth-in-advertising theory maintains that signals honestly reflect evolutionary benefits rather than handicaps.

Certain characteristics genuinely confer advantages (e.g., male muscularity, female fat deposits in breasts and hips indicating lactation ability and birth canal dimensions), while others (such as voice pitch or hair) may lack significant evolutionary relevance.

Publication history

Why Is Sex Fun? was released in 1997 by Basic Books as a title within the Science Masters series.

Reception

The book Why Is Sex Fun? garnered favorable critiques, including from biologist Steve Jones, who reviewed it in The New York Review of Books. He found the work captivating but expressed reservations regarding its discussion of concealed ovulation. Anthropologist Peter B. Gray and evolutionary biologist Justin R. Garcia recognized it as a widely read publication on human sexuality, describing it as educational yet somewhat superficial in its analysis.

Bibliography

Books

• Diamond, Jared. Why is Sex Fun? The Evolution of Human Sexuality. Basic Books, New York, 1997. ISBN 0-465-03127-7.
• Gray, Peter B., and Justin R. Garcia. Evolution and Human Sexual Behavior. Harvard University Press, Cambridge, Massachusetts and London, England, 2013. ISBN 978-0-674-07273-2.

Journals

• Jones, Steve. "Go Milk a Fruit Bat!" The New York Review of Books, vol. 44, no. 12, 1997.