Why Is Sex Fun__ The Evolution of Human Sexuality - Jared M. Diamond [30]
A simple example illustrating the goal-directed nature of sexual activity in most animal species is provided by Pied Flycatchers, the bird species I discussed in chapter 2. Normally, a female Pied Flycatcher solicits copulation only when her eggs are ready to be fertilized, a few days before laying. Once she begins egg laying, her interest in sex vanishes and she resists propositions from males or behaves indifferently toward them. But in an experiment in which a team of ornithologists made twenty female Pied Flycatchers into widows after completion of egg laying by removing their mates, six of the twenty experimental widows were seen to solicit copulation from new males within two days, three were seen actually to copulate, and more may have done so unobserved. Evidently, the females were attempting to trick the males into believing them to be fertile and available. When the eggs eventually hatched, the males would have no way of realizing that some other male had actually fathered the clutches. In at least a few cases, the trick worked, and the males proceeded to feed the hatchlings as a biological father would have. There was thus not the slightest indication that any of the females was a merry widow, pursuing sex for mere pleasure.
Since we humans are exceptional in our concealed ovulations, unceasing receptivity, and recreational sex, it can only be because we evolved to be that way. It’s especially paradoxical that in Homo sapiens, the species unique in its self-consciousness, females should be unconscious of their own ovulation, when female animals as dumb as cows are aware of it. Something special was required to conceal ovulation from a female as smart and aware as a woman. As we’ll discover, it has proven unexpectedly difficult for scientists to figure out what that special something was.
There’s a simple reason why most other animals are sensibly stingy about copulatory effort: sex is costly in energy, time, and risk of injury or death. Let me count the reasons why you should not love your beloved unnecessarily:
1. : Sperm production is sufficiently costly for males that worms with a mutation that reduces sperm production live longer than normal worms.
2. : Sex takes time that could otherwise be devoted to finding food.
3. : Couples locked in embrace risk being surprised and killed by a predator or enemy.
4. : Older individuals may succumb to the strain of sex: France’s Emperor Napoleon the Third suffered a stroke while engaged in the act, and Nelson Rockefeller died during sex.
5. : Fights between male animals competing for an estrous female often result in serious injury to the female as well as to the males.
6. : Being caught at extramarital sex is risky for many animal species, including (most notoriously) humans.
Thus, we would reap a big advantage by being as sexually efficient as other animals. What compensating advantage do we get from our apparent inefficiency?
Scientific speculation tends to center on another of our unusual features: the helpless condition of human infants makes lots of parental care necessary for many years. The young of most mammals start to get their own food as soon as they’re weaned; they become fully independent soon afterwards. Hence most female mammals can and do rear their young with no assistance from the father, whom the mother sees only to copulate. For humans, though, most food is acquired by complex technologies far beyond the dexterity or mental ability of a toddler. As a result, our children have to have food brought to them for at least a decade after weaning, and that job is much easier for two parents than for one. Even