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

And then there are, of course, chemical substances deliberately designed to shortcut the entire machinery of reward, directly stimulating the pleasure parts of the brain (for example, the nucleus accumbens). I'm speaking, of course, of alcohol, nicotine, and drugs like cocaine, heroin, and amphetamines. What is remarkable about these substances is not the fact that they exist — it would be almost impossible to build a chemically based brain that wouldntbe vulnerable to the machinations of clever chemists — but rather the extent to which people use them, even when they realize that the long-term consequences may be life threatening. The writer John Cheever, for example, once wrote, "Year after year I read in [my journals] that I am drinking too much .. . I waste more days, I suffer deep pangs of guilt, I wake up at three in the morning with the feelings of a temperance worker. Drink, its implements, environments, and effects all seem disgusting. And yet each noon I reach for the whiskey bottle."

As one psychologist put it, addictions can lead people down a "primrose path" in which decisions made in the moment seem — from the strict perspective of temporary happiness — to be rational, even though the long-term consequences are often devastating.

Even sex has its puzzling side. That sex is enjoyable is perhaps no surprise: if sex weren't fun for our ancestors, we simply wouldn't be here. Sex is, after all, the royal road to conception, and without conception there would be no life. Without life, there would be no reproduction, and legions of "selfish genes" would be out of work. It seems like a no-brainer that creatures that enjoy sex (or at least are driven toward it) will outpropagate those that do not.

But having a taste for sex is not the same as pursuing it nonstop, to the virtual exclusion of anything else. We all know stories of politicians, priests, and plain ordinary folk who destroyed their life in relentless pursuit of sex. Might a Martian question whether our contemporary need for sex is as miscalibrated as our need for sugar, salt, and fat?

The Martian would eventually come to realize that although the core notion of pleasure as motivator makes a good deal of sense, the pleasure system as a whole is a kluge, from top to bottom. If pleasure is supposed to guide us to meet the needs of our genes, why do we humans fritter away so much of our time in activities that don't advance those needs? Sure, some men may skydive to impress the ladies, but many of us ski, snowboard, or drive recklessly even when nobody else is watching. When such a large part of human activity does something that risks "reproductive fitness," there must be some explanation.

And indeed there is, but it's not about minds that are optimal, but about minds that are clumsy. The first reason should, by now, seem familiar: the neural hardware that governs pleasure is, like much of the rest of the human mind, split in two: some of our pleasure (like, perhaps, the sense of accomplishment we get from a job well done) derives from the deliberative system, but most of it doesn't. Most pleasure springs from the ancestral reflexive system, which, as we have seen, is rather shortsighted, and the weighting between the two systems still favors the ancestral. Yes, I may get a slight sense of satisfaction if I waive my opportunity to eat that crטme brlיe, but that satisfaction would almost certainly pale in comparison to the kick, however brief, that I would get from eating it.* My genes would be better off if I skipped dessert — my arteries might stay open that much longer, allowing me to gather more income and take better care of my future offspring — but those very genes, due to their lack of foresight, left me with a brain that lacks the wisdom to consistently outwit the animalistic parts of my brain, which are a holdover from an earlier era.

The second reason is more subtle: our pleasure center wasn't built for creatures as expert in culture and technology as we are; most of the mechanisms that give us pleasure are pretty crude, and in time, we've become experts at outwitting them. In an ideal world (at least from the perspective of our genes), the parts of our brain that decide which activities are pleasurable would be extremely fussy, responding only to things that are truly good for us. For example, fruits have sugar, and mammals need sugar, so it makes sense that we should

*My friend Brad, who hates to see me suffer abstemiously in the service of some abstract long-term good, likes to bring me to a restaurant called Blue Ribbon Sushi, where he invariably orders the green tea crטme brlיe. Usually, despite my best intentions, we wind up ordering two.