Dean Hamer is a happy man. you can see it in the grin that spreads across his face at the slightest provocation. Now, standing in the hallway outside his laboratory at the National Institutes of Health, Hamer is using that happiness to illustrate a point.
Today I’m only about average happy for me, he says. I found out this morning that the tenant in the house I’m buying hasn’t paid rent for a couple of months, and that started the day on a bad note. On the other hand, he’s looking forward to a date with someone he just met, and the glow of anticipation is balancing out his financial anxiety. But even on a so-so day like today, Hamer says he feels more happy than many people do on a good day. The reason, he suspects, lies in his genes. Psychologists have found that each person gravitates toward a particular degree of happiness, Hamer explains, and this level of cheerfulness and contentment is mostly a matter of heredity. So far, nobody knows which of the 100,000 genes scattered along the human genome Hamer can thank. But some years down the road, when someone pinpoints a gene that puts a spring in your step and a song in your heart, chances are pretty good that someone will be Hamer.
There isn’t a good name for what Hamer does, but it’s tempting to call him a big-gene hunter. Part molecular biologist and part psychologist, Hamer is one of a small but growing group of researchers who look for the genes that shape our individual personalities. Why does Tom plunge into a crowd of strangers at a party while Harry hangs back? Why does Rosie jump out of airplanes for fun but Paula prefers Parcheesi? Why does Charlie see the glass as half empty while Joe sees it as half full?
I believe we’ll find out something important about human behavior by studying its genetic basis, Hamer says. A wealth of studies on families and twins, he adds, show that heredity accounts for between 30 and 70 percent of the variation in personality traits among people.
Of course, that leaves another 30 to 70 percent to be accounted for by the environment, but Hamer thinks that, for now at least, piecing together the genetic side of the puzzle will have a greater payoff. It’s not even clear what the nongenetic factors are, he says. It is clear that they are not the standard things you might expect: your home environment while growing up, the schools you went to, your socioeconomic class. These are all examples of what psychologists call shared environmental factors-- things that siblings have in common--and research, Hamer says, shows they play only a small role in shaping basic personality traits. Instead, he notes, it is the environmental factors siblings don’t share--everything from one’s birth order in a family to a person’s unique life experiences-- that are most influential in forging personality, but no one knows which of these are important and which aren’t. And part of the problem, he says, is that the people who have been looking for these factors don’t take genetics into account. Only by doing so, he thinks, can we divine what role genes play in creating temperaments of every stripe.
