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

but that doesn't make it the right system for creatures like us, who do have the capacity to reason. Instead, if we humans were built from the ground up, anxiety might have no place at all: our higher-level reasoning capacities could handle planning by themselves. In a creature empowered to set and follow its own goals, it's not clear that anxiety would serve any useful function.

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.

That same mix, minus whatever inhibitory mechanisms normal people use to calm down, may exacerbate, or maybe even spawn, several other aspects of mental illness. Take, for example, the common symptom of paranoia. Once someone starts down that path — for whatever reason, legitimate or otherwise — the person may never leave it, because paranoia begets paranoia. As the old saying puts it, even the paranoid have real enemies; for an organism with confirmation bias and the will to deny counterevidence (that is, motivated reasoning), all that is necessary is one true enemy, if that. The paranoid person notices and recalls evidence that confirms his or her paranoia, discounts evidence that contradicts it, and the cycle repeats itself.

D?pressives too often lose touch with reality, but in different ways. D?pressives don't generally hallucinate (as, for example, many schizophrenics do), but they often distort their perception of reality by fixating on the negative aspects of their lives — losses, mistakes, missed opportunities, and so forth — leading to what I call a 'ruminative cycle,' one of the most common symptoms of depression. An early, well-publicized set of reports suggested that d?pressives are more realistic than happy people, but today a more considered view is that d?pressives are disordered in part because they place undue focus on negative things, often creating a downward spiral that is difficult to escape. Mark Twain once wrote, in a rare but perceptive moment of seriousness, 'Nothing that grieves us can be called little; by the eternal laws of proportion a child's loss of a doll and a king's loss of a crown are events of the same size.' Much, if not all, depression may begin with the magnification of loss, which in turn may stem directly from the ways in which memory is driven by context. Sad memories stoke sadder memories, and those generate more that are sadder still. To a person who is depressed, every fresh insult confirms a fundamental view that life is unfair or not worth living. Contextual memory thus stokes the memory of past injustices. (Meanwhile, motivated reasoning often leads d?pressives to discount evidence that would contradict their general view about the sadness of life.) Without some measure of self-control or a capacity to shift focus, the cycle may persist.

Such feedback cycles may even contribute a bit to bipolar disorder, not only in the 'down' moments but also even in the manic ('up') phases. According to Kay Redfield Jamison, a top-notch psychologist who has herself battled manic depression, when one has bipolar disorder,

there is a particular kind of pain, elation, loneliness, and terror

involved in this kind of madness . . . When you're high it's tre

mendous. The ideas and feelings are fast and frequent like shoot

ing stars .. . But, somewhere, this changes. The fast ideas are far

too fast, and there are far too many; overwhelming confusion re

places clarity... madness carves its own reality.

Without sufficient inherent capacity for cognitive and emotional control, a bipolar person in a manic state may spiral upward so far that he or she loses touch with reality. Jamison writes that in one of her early manic episodes she found herself 'in that glorious illusion of high summer days, gliding, flying, now and again lurching through cloud banks and ethers, past stars, and across fields of ice crystals .. . I remember singing 'Fly Me to the Moon' as I