Why Is Sex Fun? : A Fine Popular-Science Work on Male-Female Relations from a Biological Angle

“Be cautious not to unite with sensual forms; once sensual union occurs, misfortune arises.”

— From The Sutra of Forty-two Sections Spoken by the Buddha

Mr. Zhang Zhongxing said that the most important relationship in the human world is the relationship between the sexes. This statement finds a reasonable explanation in biology, because from the moment life began, the thing that living things on earth have had the strongest drive to do is to reproduce. We humans are animals that reproduce sexually; to reproduce our own offspring, we must cooperate with a member of the opposite sex.

Many people may have read Guns, Germs, and Steel, the classic by the famous American science writer Jared Diamond; but far fewer have read the book he wrote at the age of 59, Why Is Sex Fun? (whose Chinese translation is titled The Evolution of Sex).

This is a delightful popular-science work that explores, from a biological angle, the various questions inherent in male-female relations. For instance, why can animals accurately know when they are ovulating, whereas humans—billed as highly intelligent animals—cannot know their ovulation as accurately as animals? Animals mate only during estrus, yet why have humans turned sexual relations between the sexes into a form of entertainment that can take place at any time? The vast majority of female animals do not have a menopause; why do human women have one? Why, in the animal kingdom (humans included), does the heavy burden of raising offspring fall on the mother? And how did humanity gradually develop from a multi-male society into today's monogamous society?

Self-replication is the inner drive of genes, so all living things reproduce tirelessly. The two sexes come together to replicate their own genes, and then either cooperate, or one party bears the bitter burden alone, to ensure that their offspring survive. In most human societies, children are raised by both parents, though some unlucky infants are raised by a single parent or become orphans raised by society. Usually, when both parents raise the children, the offspring's chance of survival is greater. Precisely because of this, both parents in humans and many animals raise the young.

But for viviparous animals, the mother can be certain that the child she bears is truly her own, whereas the father cannot. So fathers are always suspicious and not as actively caring toward offspring as mothers. To help children keep their father around to raise the young together, most female animals have devised all manner of strategies.

In a lion pride, only the lion king can mate with all the females; no other male lion may mate with a lioness. So the lion king knows that all the cubs in the pride are his own offspring. Once the pride undergoes a “regime change”—when the new lion king defeats the old one—the new king will kill all the cubs without hesitation, and then mate with the lionesses to produce new cubs. Because he knows the cubs sired by the old king are not his own descendants, the new lion king will not waste time and energy caring for cubs that are not his own.

This cruel practice of killing infants exists not only in lion prides but was once widespread across the animal kingdom. Mothers cannot bear to see their own offspring killed, so in some species females mate one by one with the males in the group. That way each male believes the infants borne by these females are his own offspring, and will not indiscriminately kill the innocent; scientists call such a society a multi-father society. Our human ancestors also passed through a multi-father society era; only in the course of evolution did monogamy gradually form, with both husband and wife reproducing and raising offspring together. In most cases, human infants are indeed the joint offspring of both parents; a child is the strongest bond connecting the parents.

The period of growth for human infants is long. During a child's growth, the mother is unable simultaneously to protect her child and to forage for food for it. So mothers need to keep fathers around, bearing the responsibility of raising the children rather than roaming in search of new mates. To this end, humans gradually evolved the trait of not knowing one's exact ovulation and being able to engage in sexual activity at any time.

It is also because bearing children is such a high-risk undertaking that human women gradually lose fertility after the age of forty, and by fifty can no longer bear children; otherwise the risk to offspring's survival would be too great. Elderly female mice, chimpanzees and elephants can all reproduce normally; only humans and whales have a menopause, and this is because our human infants need their mothers' care for a longer time.

Probably only humans can escape the fate nature has arranged, voluntarily choosing not to reproduce. The DINK (dual income, no kids) crowd, and those who become ascetics before they have had children, voluntarily give up the chance to replicate their genes. Because humans have realized that bearing offspring is an arduous undertaking and that caring for infants shortens the parents' lifespan.

Likewise, mating shortens the life of male animals, because males must expend a great deal of biochemical energy to produce sperm. A female's supply of eggs is fixed from birth, decreasing by a certain amount with each ovulation until at last no eggs remain. But males can keep producing new sperm to mate; only this is a losing proposition, so most male animals do not, like humans, waste their biochemical energy mating outside the female's estrus. Abstinence does indeed allow men to live somewhat longer.

Probing deeply into the motivations behind human behavior is a fascinating thing; once we understand these, we will be more tolerant and understanding of many of our partners' behaviors. For example, we may reproach women for being too materialistic, but in fact this is merely an instinct of living things: all mothers are trying to secure and stockpile more survival resources for their offspring so as to guarantee reproductive success. Understanding this, husbands and fathers become less resistant to the nagging that so often occurs in families; what we should do most is to reassure the child's mother that our common offspring will be properly cared for. Women, for their part, should know that their spouse's suspiciousness is also a biological instinct; they are merely worrying that what they have labored to raise may not be their own offspring.

Personally, after reading this book, I smiled to myself, because I gained a brand-new understanding of many questions in male-female relations. Many couples live at daggers drawn, perhaps because they mistake the biological drives of each sex for “character flaws,” with the result that they bicker constantly, trying to change each other's biological instincts. Perhaps, if these problems are viewed from a different angle, both husband and wife will find it easier to be at peace. Spiritual aspirations are beautiful and endless, but biological laws also objectively exist.