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

One could make a similar argument about the human need for self-esteem, social approval, and rank — collectively, the source of much psychological distress. Perhaps in any world we could imagine, it would be to most creatures' benefit to secure social approval, but it is not clear why a lack of social approval ought necessarily to result in emotional pain. Why not be like the Buddhist robots I conjured in

^Evolution is also flagrantly unconcerned with the lives of those past child-bearing age; genes that predispose people to Huntington's chorea or Alzheimer's disease could bear some hidden benefit, but the disorder could persist even if it didn't, simply because, as something that happens late in life, the bottom line of reproductive fitness isn't affected.

the last chapter, always aware of (and responsive to) circumstances, but never troubled by them?

Science fiction? Who knows. What these thought experiments do tell us is that it is possible to imagine other ways in which creatures might live and breathe, and it's not clear that the disorders we see would inevitably evolve in those creatures.

What I am hinting at, of course, is this: the possibility that mental illness might stem, at least in part, from accidents of our evolutionary history. Consider, for example, our species-wide vulnerability to addiction, be it to cigarettes, alcohol, cocaine, sex, gambling, video games, chat rooms, or the Internet. Addiction can arise when short-term benefits appear subjectively enormous (as with heroin, often described as being better than sex), when long-term benefits appear subjectively small (to people otherwise depressed, who see themselves as having little to live for), or when the brain fails to properly compute the ratio between the two. (The latter seems to happen in some patients with lesions in the ventromedial prefrontal cortex, who evidently can detect costs and benefits but seem indifferent as to their ratio.) In each case, addiction can be thought of as a particular case of a general problem: our species-wide difficulty in balancing ancestral and modern systems of self-control.

To be sure, other factors are at work, such as the amount of pleasure a given individual gets from a given activity; some people get a kick out of gambling, and others would rather just save their pennies. Different people are vulnerable to different addictions, and to different degrees. But we are all at least somewhat at risk. Once the balance between long-term and short was left to a rather unprincipled tug-ofwar, humanity's vulnerability to addiction may have become all but inevitable.

If the split in our systems of self-control represents one kind of fault line in the human mind, confirmation bias and motivated reasoning combine to form another: the relative ease with which humans can lose touch with reality. When we "lose it" or "blow things out of proportion," we lose perspective, getting so angry, for example, that all traces of objectivity vanish. It's not one of our virtues, but it is a part of being human; we are clearly a hotheaded species.

That said, most of the time, most of us get over it; we may lose touch in the course of an argument, but ultimately we take a deep breath or get a good night's sleep, and move on. ("Yes, it was really lousy of you to stay out all night and not call, but I admit that when I said you never call I might have been exaggerating. Slightly." Or, as Christine Lavin once sang, "I'm sorry, forgive me, . . . but I'm still mad at you.")

What occasionally allows normal people to spiral out of control is a witch's brew of cognitive kluges: (1) the clumsy apparatus of self-control (which in the heat of the moment all too often gives the upper hand to our reflexive system); (2) the lunacy of confirmation bias (which convinces us that we are always right, or nearly so); (3) its evil twin, motivated reasoning (which leads us to protect our beliefs, even those beliefs that are dubious); and (4) the contextually driven nature of memory (such that when we're angry at someone, we tend to remember other things about them that have made us angry in the past). In short, this leaves "hot" systems dominating cool reason; carnage often ensues.