If you’ve got a few minutes to spare, then you may enjoy this New Republic article on the phenomenon of loneliness and its impact on physical health. It’s full of all sorts of interesting asides about who experiences loneliness and why.
A famous experiment helps explain why rejection makes us flinch. It was conducted more than a decade ago by Naomi Eisenberger, a social psychologist at UCLA, along with her colleagues. People were brought one-by-one into the lab to play a multiplayer online game called “Cyberball” that involved tossing a ball back and forth with two other “people,” who weren’t actually people at all, but a computer program. “They” played nicely with the real person for a while, then proceeded to ignore her, throwing the ball only to each other. Functional magnetic resonance imaging scans showed that the experience of being snubbed lit up a part of the subjects’ brains (the dorsal anterior cingulate cortex) that also lights up when the body feels physical pain.
I asked Eisenberger why, if the same part of our brain processes social insult and bodily injury, we don’t confuse the two. She explained that physical harm simultaneously lights up another neural region as well, one whose job is to locate the ache—on an arm or leg, inside the body, and so on. What the dorsal anterior cingulate cortex registers is the emotional fact that pain is distressing, be it social or physical. She calls this the “affective component” of pain. In operations performed to relieve chronic pain, doctors have lesioned, or disabled, the dorsal anterior cingulate cortex. After the surgery, the patients report that they can still sense where the trouble comes from, but, they add, it just doesn’t bother them anymore.
It’s tempting to say that the lonely were born that way—it’d let the rest of us off the hook. And, as it turns out, we’d be about half right, because loneliness is about half heritable. A longitudinal study of more than 8,000 identical Dutch twins found that, if one twin reported feeling lonely and unloved, the other twin would report the same thing 48 percent of the time. This figure held so steady across the pairs of twins—young or old, male or female, notwithstanding different upbringings—that researchers concluded that it had to reflect genetic, not environmental, influence. To understand what it means for a personality trait to have 48 percent heritability, consider that the influence of genes on a purely physical trait is 100 percent. Children get the color of their eyes from their parents, and that is that. But although genes may predispose children toward loneliness, they do not account for everything that makes them grow up lonely. Fifty-two percent of that comes from the world.
Evolutionary theory, which has a story for everything, has a story to illustrate how the human species might benefit from wide variations in temperament. A group that included different personality types would be more likely to survive a radical change in social conditions than a group in which everyone was exactly alike. Imagine that, after years in which a group had lived in peace, an army of strangers suddenly appeared on the horizon. The tribe in which some men stayed behind while the rest headed off on a month-long hunting expedition (the stay-at-homes may have been less adventurous, or they may just have been loners) had a better chance of repelling the invaders, or at least of saving the children, than the tribe whose men had all enthusiastically wandered off, confident that everything would be fine back home.