We like to think of ourselves as rational creatures. We watch our backs, weigh the odds, pack an umbrella. But both neuroscience and social science suggest that we are more optimistic than realistic. On average, we expect things to turn out better than they wind up being. People hugely underestimate their chances of getting divorced, losing their job or being diagnosed with cancer; expect their children to be extraordinarily gifted; envision themselves achieving more than their peers; and overestimate their likely life span (sometimes by 20 years or more).

The belief that the future will be much better than the past and present is known as the optimism bias. It abides in every race, region and socioeconomic bracket. (1)Schoolchildren playing when-I-grow-up are rampant optimists, but so are grown-ups: A 2005 study found that adults over 60 are just as likely to see the glass half full as young adults.

You might expect optimism to erode under the tide of news about violent conflicts, high unemployment, tornadoes and floods and all the threats and failures that shape human life. Collectively we can grow pessimistic-about the direction of our country or the ability of our leaders to improve education and reduce crime. But private optimism, about our personal future, remains incredibly resilient. A survey conducted in 2007 found that while 70% thought families in general were less successful than in their parents' day. 76% of respondents were optimistic about the future of their own family.

Overly positive assumptions can lead to disastrous miscalculations-make us less likely to get health checkups, apply sunscreen or open a savings account, and more likely to bet the farm on a bad investment. But the bias also protects and inspires us: It keeps us moving forward rather than to the nearest high-rise ledge*. (2)Without optimism, our ancestors might never have ventured far from their tribes and we might all be cave dwellers, still huddled together and dreaming of light and heat.

To make progress, we need to be able to imagine alternative realities-better ones-and we need to believe that we can achieve them. Such faith helps motivate us to pursue our goals. Optimists in general work longer hours and tend to earn more. Economists at Duke University found that optimists even save more. And although they are not less likely to divorce, they are more likely to remarry.

Even if that better future is often an illusion, optimism has clear benefits in the present. Hope keeps our minds at ease, lowers stress and improves physical health. Researchers studying heart-disease patients found that optimists were more likely than nonoptimistic patients to take vitamins, eat low-fat diets and exercise, thereby reducing their overall coronary risk. A study of cancer patients revealed that pessimistic patients under the age of 60 were more likely to die within eight months than nonpessimistic patients of the same initial health. status and age.

In fact, a growing body of scientific evidence points to the conclusion that optimism may be hardwired by evolution into the human brain. The science of optimism, once scorned as an intellectually suspect province of pep rallies** and smiley faces, is opening a new window on the workings of human consciousness. (3)What it shows could fuel a revolution in psychology, as the field comes to grips with accumulating evidence that our brains aren’t just stamped by the past. They are constantly being shaped by the future.

• *ledge: a narrow horizontal surface projecting from a wall, cliff, or other surface
• **pep rally: a meeting at a school before a sports event, when cheerleaders lead the students in encouraging their team to win