Unhappy? Blame biology. Then cheer yourself up by finding a job with a shorter commute.

As economists, psychologists and biologists try to determine what makes a person happy or unhappy, one factor stands out as especially powerful. To a large degree, it seems, happiness is inherited.

The strongest evidence comes from a study of identical twins conducted by David Lykken, now a professor emeritus at the University of Minnesota.

Some 60% of the likelihood that twins separated at birth will describe themselves as happy is accounted for by common genetic factors, not environmental differences in their lives.

This doesn't argue for a "happiness gene." Obesity also is heavily influenced by genetics, notes Carnegie Mellon economist George Loewenstein, but that doesn't negate environment's role--or explain why Americans are so much fatter than Europeans.

But biology may play a huge role in happiness, through an untold number of genes involved in forming personality. Which means that economists in this field may have much to learn from biologists. Tim Ketelaar, a psychologist at New Mexico State University, notes that economists discovered that losses loom much larger than gains in our decisions--and Ketelaar's own work has shown that the same holds true for students' grades.

Those with high grades aren't happier than those with low ones, but both groups are upset when their grades drop. Economists were surprised by this, but ecologists studying birds discovered the same thing. A misstep costs an animal the future, while a success helps it only a little.

Another shocker that shouldn't have been: Wealth levels have a limited impact on happiness. Again, this is no surprise to biologists, Ketelaar says, because money is a relatively recent development in the history of human evolution. "Of course individuals aren't built to track wealth," he says. "Prior to agriculture, you couldn't have a society that could amass wealth."

Clues to our behaviors can be found in the brain chemical dopamine, which is the key to the body's reward system. Strangely, in chimpanzees, dopamine levels peak not when they are going to get an award but when they realize the award is coming. That's very similar to our response to money.

For chimpanzees, this kind of brain chemistry can lead to strange behavior. In an essay, Stanford biologist Robert Sapolsky described a chimp that chased a prospective mate far beyond what would be reasonable, because the mate dropped occasional signals that she might be willing--maybe, someday. Sapolsky referred to this as the "pleasure and pain of maybe." The chimp was willing to go to great lengths for a hypothetical reward.

But humans also behave with a similar bizarreness. Take commuting--one of the strangest activities in modern life. Jobs turn out to be critically important to happiness--unemployed people are very unhappy, statistically speaking. But commuting takes some bloom off that rose. A study by researchers at the University of Zurich that was released this year found that commuters underwent more stress as a result of their daily travels than could possibly be paid for by any benefits they got by being willing to travel so far. The hypothetical reward--the good job--winds up outweighing the daily grind of commuting, even though it shouldn't.

However, for all the importance of biology, better living through chemistry doesn't lead to happiness. A 1998 study by Brian Knutson, now a professor at Stanford, showed that antidepressants do reduce negative emotions, such as anxiety and fear. And they actually have a powerful effect on patients' personalities, making them more engaged and cooperative in completing a lab test--something that could lead to happiness in the long run. But Knutson's research also revealed that antidepressants such as Prozac or Paxil did not seem to boost optimism or extroversion.

There's an upside to the biological nature of glee. Around the world, about two-thirds of people say they are happy, according to Nancy Etcoff, a psychologist at Harvard Medical School who is writing a book about happiness. Optimism has shown to be a helpful trait that can help people survive traumatic experiences such as heart bypass surgery. Says Etcoff, "There may be some innate tendency to be happy."

That, at least, is something to smile about.

(Agencies September 27, 2004)