Kluge: The Haphazard Construction of the Human Mind (Houghton Mifflin; 2008)

*That said, when it comes to reasons for having sex, pleasure and reproduction are, at least for humans, just two motivations among many. The most comprehensive survey ever conducted, reported recently in the Archives of Sexual Behavior, listed a grand total of 237. Seeking pleasure and making babies were definitely on the list, but so were "it seemed like good exercise," "I wanted to be popular," "I was bored," "I wanted to say thank you," and "I wanted to feel closer to God." One way or another, 96 percent of American adults have at least once found some reason for having sex.

ing effect for the word water than people who are well hydrated. This occurs over the course of a few milliseconds, allowing pleasure to serve as a moment-by-moment guide. Similar findings — and this is the scary part — apply even in our attitudes toward other people: the more we need them, the more we like them. (To rather cynically paraphrase an old expression, from the perspective of the subconscious, a friend we need is a friend perceived.)

But the simple idea that "if it feels good, it must have been good for our ancestors" runs into trouble pretty quickly. To start with, many — arguably, most — things that give us pleasure don't actually do much for our genes. In the United States, the average adult spends nearly a third of his or her waking hours on leisure activities such as television, sports, drinking with friends — pursuits that may have little or no direct genetic benefit. Even sex, most of the time for most people, is recreational, not procreational. When I spend $100 on a meal at Sushi Samba, my favorite restaurant du jour, I don't do it because it will increase the number of kids I have, or because eating Peruvian-Japanese fusion food is the cheapest (or even most nutritious) way to fill my belly. I do it because, well, I like the taste of yellowtail ceviche — even if, from the perspective of evolution, my dining bills are a waste of precious financial resources.

A Martian looking down on planet Earth might note all this with puzzlement. Why do humans fool around so much when there is, inevitably, work to be done? Although other species have been known to play, no other species goofs around so much, or in so many ways. Only a few other species seem to spend much time having non-procreative sex, and none (outside labs run by inquisitive humans) watch television, go to rock concerts, or play organized sports. Which raises the question, is pleasure really an ideal adaptation, or (with apologies to Shakespeare) is there something klugey in Denmark?

Aha, says our Martian to itself; humans are no longer slaves to their genes. Instead of engaging in the activities that would yield the most copies of their genes, humans are trying to maximize something else, something more abstract — call it "happiness" — which appears to be a measure of factors such as a human's general well-being, its level of success, its perceived control over its own life, and how well it is regarded by its peers.

At which point, our Martian friend would be even more confused. If people are trying to maximize their overall well-being, why do they do so many things that in the long run yield little or no lasting happiness?

Perhaps nothing would puzzle this Martian more than the enormous amount of time that many people spend watching television. In America, the average is 2-4 hours per day. If you consider that the average person is awake for only 16, and at work for at least 8, that's a huge proportion of the average person's discretionary time. Yet day after day, audiences watch show after show, most containing either stories of dubious quality about fictional people or heavily edited "reality" portraits of people in improbable situations that the average viewer is unlikely ever to meet. (Yes, public television airs some great documentaries, but they never draw the ratings of Law & Order, Lost, or Survivor.) And here's the kicker: hard-core television watchers are, on average, less happy than those who watch only a little television. All that TV viewing might convey some sort of short-term benefit, but in the long term, an hour spent watching television is an hour that could have been spent doing something else — exercising, working on hobbies, caring for children, helping strangers, or developing friendships.