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

Depression (and perhaps bipolar disorder) is probably also aggravated by another one of evolution's glitches: the degree to which we depend on the somewhat quirky apparatus of pleasure. As we saw in the previous chapter, long before sophisticated deliberative reasoning arose, our pre-hominid ancestors presumably set their goals primarily by following the compass of pleasure (and avoiding its antithesis, pain). Even though modern humans have more sophisticated machinery for setting goals, pleasure and plain probably still form the core of our goal-setting apparatus. In dיpressives, this may yield a kind of double-whammy; in addition to the immediate pain of depression, another symptom that often arises is paralysis. Why? Quite possibly because the internal compass of pleasure becomes nonresponsive, leaving sufferers with little motivation, nothing to steer toward. For an organism that kept its mood separate from its goals, the dysfunction often accompanying depression might simply not occur.

In short, many aspects of mental illness may be traced to, or at least intensified by, some of the quirks of our evolution: contextual memory, the distorting effects of confirmation bias and motivated reasoning, and the peculiar split in our systems of self-control. A fourth contributor may be our species' thirst for explanation, which often leads us to build stories out of a sparse set of facts. Just as a gambler may seek to "explain" every roll of the dice, people afflicted with schizophrenia may use the cognitive machinery of explanation to piece together voices and delusions. This is not to say that people with disorders aren't different from healthy folks, but rather that their disorders may well have their beginnings in neural vulnerabilities that we all share.

Perhaps it is no accident, then, that so much of the advice given by cognitive-behavioral therapists for treating depression consists of getting people to cope with ordinary human failures in reasoning. David Burns's well-known Feeling Good Handbook, for example, suggests that ten basic cognitive errors, such as "overgeneralization" and "personalization," are made by people who are anxious or depressed. Overgeneralization is the process of erroneously "seeing a single event as a part of a never-ending pattern of defeat"; personalization is the mistake of assuming that we (rather than external events) are responsible for anything bad that happens. Both errors probably stem in part from the human tendency to extrapolate excessively from small amounts of highly salient data. One setback does not a miserable life make, yet it's human to treat the latest, worst news as an omen, as if a whole life of cyclical ups and downs is negated by a single vivid disaster. Such misapprehensions might simply not exist in a species capable of assigning equal mental weight to confirming and disaffirming evidence.

I don't mean to say that depression (or any disorder) is purely a byproduct of limitations in our abilities to objectively evaluate data, but the clumsy mechanics of our klugey mind very likely lay some of the shaky groundwork.

If disorders extend from fault lines, they certainly move beyond them too. To the extent that genes clearly play a role in mental disorders, evolution is in some way — adaptively or otherwise — implicated. But our mental fault lines sometimes give rise to earthquakes, though at other times only tiny tremblors, scarcely felt. Evolution, however haphazard, can't possibly be the whole story. Most common mental disorders seem to depend on a genetic component, shaped by evolution — but also on environmental causes that are not well understood. If one identical twin has, say, schizophrenia, the other one is considerably more likely than average to also have it, but the so-called "concordance" percentage, the chance that one twin will have the disorder if the other does, is only about 50 percent. For that reason alone it would clearly be overreaching to ascribe every aspect of mental illness to the idiosyncrasies of evolution.

But at the same time, it seems safe to say that no intelligent and compassionate designer would have built the human mind to be quite as vulnerable as it is. Our mental fragility provides yet another reason to doubt that we are the product of deliberate design rather than chance and evolution.

Which brings us to one last question, perhaps the most important of all: if the mind is a kluge, is there anything can we do about it?

8

TRUE WISDOM

God grant me the serenity to accept the things I cannot change, courage to change the things I can, and wisdom to know the difference.

— REINHOLD NIEBUHR

To know that one knows what one knows, and to know that one doesn't know what one doesn't know, there lies true wisdom.

— CONFUCIUS