by Daniel Gilbert
Alfred A. Knopf, 2006

by Jonathan Haidt
Basic Books, 2006

by Darrin M. McMahon
Atlantic Monthly Press, 2006

The sky was smeared with the lights from the midway, spinning, blinking, beckoning to risk takers, but I decided to go for a different kind of thrill: Ronnie and Donnie Galyon, the Siamese Twins, were at the Minnesota State Fair. Feeling some guilt, I bought my ticket and cautiously approached the window of the trailer they called home. Thirty years old, joined at the stomach, they were sitting on a sofa, craning their necks to watch television.

Twenty-five years later I am still struck by this dizzying conjunction of the grotesque and the mundane. Trying to project myself into their situation--a man with two heads, two men with one body--I felt only sickness, horror and a certainty that I would rather be dead. Yet there they were, traveling from town to town, leading some kind of life.

When we try to envision another's happiness, we suffer from arrogance and a poverty of imagination. In 1997, when science writer Natalie Angier interviewed Lori and Reba Schappell, connected at the back of the head and sporting different hairdos, each insisted that she was basically content.

"There are good days and bad days--so what?" Reba said. "This is what we know. We don't hate it. We live it every day." Lori was as emphatic: "People come up to me and say, 'You're such an inspiration. Now I realize how minor my own problems are compared to yours.' But they have no idea what problems I have or don't have, or what my life is like.''

Three recent books--two by scientists and one by a historian--take on the quest for the good life, in which common sense and the received wisdom of the ages is increasingly confronted by findings from psychology, neuroscience and genetics.

In the fight for survival, evolution has naturally molded our nervous systems to respond more quickly to the negative than to the positive. Before the late-blooming forebrain can reason that the hiss we hear is from an espresso machine, the primitive amygdala whispers "snake." Depending on which part of the brain is paid more heed, a person will tend to be glum and anxious or cheerful and daring, but the choice may be beyond control.

Each of us, it seems, has an emotional "set point" or "cognitive style" that is genetically rooted and hard to budge. In The Happiness Hypothesis, Jonathan Haidt, a psychologist at the University of Virginia, observes that lottery winners and paralysis victims quickly return to equilibrium, regaining the level of joy--or sadness--they felt before their brush with fate. How Ronnie, Donnie, Lori, Reba and the rest of us feel about life may depend less on circumstance than on natural disposition, the shape of the brain.

Knowing nothing of neurology, the ancient Greeks equated happiness with being favored by the gods, something over which they were powerless. This fatalism is frozen in our language. Happiness, happenstance, haphazard, hapless--all derive from the same root. In Happiness: A History, Darrin M. McMahon, a historian at Florida State University, charts how this germ of an idea changed over time. With Christianity, happiness became something to aspire to in the afterlife, and with the Enlightenment something to pursue on earth. From there it was a natural progression to the smiley face (invented in 1963, McMahon tells us, by one Harvey R. Ball) and the decision by the country of Bhutan to measure its economy according to "gross national happiness."

With evolutionary biology we have come, full circle, back to the Greeks: happiness is in the luck of the draw, how we fare in the genetic sweepstakes, the modern name for Fortuna's wheel. Not even geography or economic position is as influential a factor. Several years ago in the journal Science & Spirit, another psychologist, Robert Biswas-Diener, wrote about the remarkably high spirits he found among people in a Calcutta slum and on the harsh northern coast of Greenland. "Research shows that we are the fortunate inheritors of a highly evolved emotional system that leads us to be, for the most part, somewhat happy," he wrote. "We have a tendency to interpret things positively and to adjust quickly to most events."

The downside is that this reflexive optimism can keep us from making good guesses about what will or will not bring us joy. It is not just the hard lives of others that we have trouble imagining but also our own. In Stumbling on Happiness, Daniel Gilbert, a Harvard psychologist studying "affective forecasting," shows that people have inflated expectations about the joy they will derive from a vacation, a new car or child, or a second dessert. But our failure as futurists also cuts the other way. We overestimate how bad we will feel if we get fired or lose a tooth or even a friend or mate. Rationalization, our emotional immune system, insists on putting the best face possible on even the saddest events.

"We treat our future selves as though they were our children," Gilbert writes, "spending most of the hours of most of our days constructing tomorrows that we hope will make them happy." But the children turn out to be ingrates, complaining that we should have let them stay in the old house or study dentistry instead of law.

Taken together, all these findings may seem a little depressing. But true to our nature, we can see them in a sunnier way. A whole industry has sprung up--mass-market therapy, cosmetics, cheap luxury cruises--promoting a kind of gross national sappiness, an obligation to have fun. A little knowledge from the psych labs may take off some of the pressure, providing grist for the inverse of a self-help book--not a guide on how to achieve happiness but on understanding why, in the end, you probably won't.

George Johnson's most recent book is Miss Leavitt's Stars: The Unknown Story of the Woman Who Discovered How to Measure the Universe (W. W. Norton, 2005).