Evolution may explain need for privacy during sex

If scientists from another planet were trying to understand us, our obsession with privacy during sex would make a good thesis project.

The aliens might have noticed that most humans prefer to copulate while hidden away — our cozy bedrooms or perhaps a desolate beach dappled with moonbeams. Much fuss ensues when someone chooses to perform mating behavior more publicly, say in a sex club, or in front of a dormitory window, as was the case recently at the University of Pennsylvania.

Why, the aliens might wonder, would crowds of humans gather to watch and photograph a pair of other humans at Penn who repeatedly failed to draw their curtains before engaging in intercourse?

Why were they then so distressed about attracting a slightly wider audience when pictures circulated on the Web showing their naked backsides making the beast with two backs, as Shakespeare would say.

Then there was the scandal that started when a TV station secretly planted cameras in the Philadelphia sex club Kama Sutra, outraging patrons who go there to get some privacy while they have sex in large rooms full of other people.

Both incidents open up huge anthropological and sociobiological questions. Most animals don't care whether anyone watches them mating. They neither seek out nor avoid an audience. What's with the humans?

In societies from the sands of the Kalahari to the tiniest Pacific Islands, the cultural preference is for sex in private, says J. Christopher Kovats-Bernat, an anthropologist from Muhlenberg College in Allentown, Pa. Where people can afford it, "we segregate off a space in the dwelling that is devoted to two things — sleeping and sex." In many parts of the world, however, the private bedroom is an unattainable luxury.

While members of Kama Sutra reportedly pay $100 for the privilege of having sex in front of other people, couples in Japan are paying to be alone. There, extended families pack into single room apartments, so a cottage industry has sprung up to provide "love hotels," says Kovats-Bernat. These by-the-hour rentals cater mostly to married couples.

The Serino people of Bolivia also like privacy, but they sleep in common rooms in rows of hammocks, he says. So if one couple starts having sex, the neighbors will politely turn the other way.

And yet, many subcultures exist in which people seek out a certain lack of privacy. In Jamaica, Kovats-Bernat said, strip clubs offer something called "freaky sex" in which men get up on stage, strip and have sex with the dancers. Either way, we seem to care whether people are watching us or not, which makes us quite different from, say, dogs, who couldn't care less.

In his book "Why is Sex Fun," UCLA professor and noted author Jared Diamond explains why you and your dog will never understand each other's sex lives. No self-respecting dog would need to hide while mating, he says. Dogs also refrain from sex unless the female is in her fertile phase.

According to Diamond's book, our ape relatives routinely have sex in group settings but, like dogs, only when the female is in estrus. While the Catholic Church promotes the idea that sex is for procreation, Diamond notes that's much more the case with chimps and dogs, who aren't interested unless they're likely to conceive.

Humans, for some reason, evolved so that men and women want to mate all month long even though women are fertile for only a few days, which are hard to identify.

Diamond connects our "concealed ovulation" with our desire for concealed copulation and outlines a couple of theories explaining why they evolved. One suggests the urge for privacy arose because it prevents conflict and thereby encourages group cohesion needed for successful hunting and gathering.

Illustrating with a more modern example, he writes that if it was an everyday occurrence for people to go into heat, get naked and full-out copulate, say, on the office couch, we just wouldn't get that much work done.

Faye Flam's Carnal Knowledge column appears Wednesdays in

The Seattle Times.