People adapt to hedonic pleasures in their lives and return to their baseline level of happiness. This relationship also holds true for society at large, as demonstrated by what's called the "progress paradox": Despite significant progress and economic growth over the past 50 years, happiness levels have remained relatively constant or declined.

The good news is that the genetic basis of happiness accounts for about only 50 percent of people's happiness levels. However, the things that we think would make us happy-- such as more money, a bigger house, a newer car, or the latest electronic gadget--really don't contribute that much to happiness. Taken together, the circumstances of life, including wealth, marriage, health, attractiveness, and education level, account for only 10 percent of our happiness because we habituate to our circumstances. Big changes quickly become a normal part of life, and we return to our happiness set point.

MORE ISN'T BETTER

There are a few qualifications to the general rule that money doesn't buy happiness. Money is related to happiness when people do not have enough money to meet basic needs for food, shelter, and clothing and still have a little left over for non-essentials. But a new study by Nobel Prize winner Daniel Kahneman at Princeton University identified $75,000 (depending upon where you live) as the income above which the relationship between happiness and income basically disappears. More income does not translate to being happier.

Another qualification to the money-doesn't-buy-happiness idea is that there are multiple ways of viewing happiness. Having a higher income is not related to the moment-by-moment positive feelings we associate with happiness; however, it does increase people's overall satisfaction with their lives or view of themselves as successful.

So, if about 50 percent of happiness is explained by our genes and 10 percent by our life circumstances, what accounts for the remaining 40 percent? Researchers are starting to view happiness as similar to weight loss. There is a genetic basis for the weight that each person's body will tend to maintain (again, a set point), which is often higher than we'd like. In order to lose weight, we must make lifestyle changes to diet and activity levels.