Psychologists have been fond of stating in recent years that human happiness, or what psychologists call subjective well-being, is largely independent of our life circumstances. The wealthy aren't much happier than the middle class, married people aren't much happier than single people, healthy people aren't much happier than sick people, and so on.

One might reasonably conclude, therefore, that changes in life circumstances would not have long-term effects on our happiness. This indeed has been the dominant model of subjective well-being: People adapt to major life events, both positive and negative, and our happiness pretty much stays constant through our lives, even if it is occasionally perturbed. Winning the lottery won't make you happier in the long run (goes the theory), and while a divorce or even a major illness will throw your life into upheaval for a while, your happiness level will eventually return to where it was at before--that is, its set point.

But new research, and reexamination of old research, is challenging some of the claims of set-point theory.

In the April issue of Current Directions in Psychological Science, Richard E. Lucas of Michigan State University and the German Institute for Economic Research, reviews some recent studies suggesting that adaptation to changing life circumstances only goes so far. "Happiness levels do change, adaptation is not inevitable, and life events do matter," Lucas asserts.

To study adaptation, Lucas and his colleagues used data from two large national prospective panel studies -- one in Germany and the other in Great Britain. Unlike most previous studies of adaptation, these data were able to capture levels of life satisfaction both prior to and after major life events like marriage, divorce, unemployment, and illness or disability.

Lucas found that not all of life's slings and arrows are created equal. On average, most people adapt quickly to marriage, for example -- within just a couple of years, the peak in subjective well-being experienced around the time of getting married returns to its previous levels. People mostly adapt to the sorrows of losing a spouse too, but this takes longer -- about 7 years. People who get divorced and people who become unemployed, however, do not, on average, return to the level of happiness they were at previously. The same can be said about physical debilitation. Numerous recent studies have demonstrated that major illnesses and injury result in significant, lasting decreases in subjective-well being.

But Lucas also found that individual differences play an important role. There's a lot of individual variation in the degree to which people adapt to what life throws at them. What's more, individuals destined to experience certain life events actually differ in their subjective well-being from those not so fated -- even well before the occurrence of those events. People who eventually marry and stay married, for example, tend to be happier even 5 years before their marriage than those who are destined to marry and get divorced.

Lucas stresses that his findings do not undercut the importance of adaptation processes. Some degree of adaptation necessarily protects us from prolonged emotional states that may be harmful, and helps us attune to novel threats to our well-being rather than dwell on ones we are familiar with. Adaptation also helps us detach from goals that have proven unrealistic.