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Still, there is always a flip side. People have enemies--social rivals--as well as friends, feel resentful as well as grateful, feel nervously suspicious as well as trusting. Their children, being genetic conduits, can make them inordinately proud but also inordinately disappointed, angry or anxious. People feel the thrill of victory but also the agony of defeat, not to mention pregame jitters. According to evolutionary psychology, such unpleasant feelings are with us today because they helped our ancestors get genes into the next generation. Anxiety goaded them into keeping their children out of harm's way or adding to food stocks even amid plenty. Sadness or dejection--after a high-profile social failure, say--led to soul-searching that might discourage repeating the behavior that led to the failure. ("Maybe flirting with the wives of men larger than me isn't a good idea.") The past usefulness of unpleasant feelings is the reason periodic unhappiness is a natural condition, found in every culture, impossible to escape.
What isn't natural is going crazy--for sadness to linger on into debilitating depression, for anxiety to grow chronic and paralyzing. These are largely diseases of modernity. When researchers examined rural villagers in Samoa, they discovered what were by Western standards extraordinarily low levels of cortisol, a biochemical by-product of anxiety. And when a Western anthropologist tried to study depression among the Kaluli of New Guinea, he couldn't find any.
One thing that helps turn the perfectly natural feeling of sadness or dejection into the pathology known as depression is social isolation. Today one-fourth of American households consist of a single person. That's up from 8% in 1940--and, apparently, from roughly zero percent in the ancestral environment. Hunter-gatherer societies, for all their diversity, typically feature intimacy and stability: people live in close contact with roughly the same array of several dozen friends and relatives for decades. They may move to another village, but usually either to join a new family network (as upon marriage) or to return to an old one (as upon separation). The evolutionary psychologists John Tooby and Leda Cosmides see in the mammoth popularity of the TV show Cheers during the 1980s a visceral yearning for the world of our ancestors--a place where life brought regular, random encounters with friends, and not just occasional, carefully scheduled lunches with them; where there were spats and rivalries, yes, but where grievances were usually heard in short order and tensions thus resolved.
As anyone who has lived in a small town can attest, social intimacy comes at the price of privacy: everybody knows your business. And that's true in spades when next-door neighbors live not in Norman Rockwell clapboard homes but in thatched huts.