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It's been said that a man dies simply because he doesn't know how to live longer. Well, thank goodness for progress.

People are living longer these days. According to the Centers for Disease Control, in 1920 the average life expectancy was 54. Today, people can expect to live to 78.

Feel free to speculate about why--better food supply, better medical care, better hygiene or any number of other factors. It's not totally clear to scientists how they all add up. But what we do know is that studies are finding genetics don't tell the whole story when it comes to which diseases will likely kill us.

"There's a saying that genetics load the gun, but it's the environment that pulls the trigger," says Dr. David Fein, medical director at the Princeton Longevity Center, a clinic in Princeton, N.J., which focuses on quality of life and prolonging it. "You can have the gene for a certain disease, but it doesn't mean you're going to get it."

Take heed: Your lifestyle choices are very significant. While there is no way to ultimately defy death, that isn't an excuse to start indulging in vices and neglecting your health. There are plenty of ways to keep the grim reaper at bay--and many of these "secrets" result in an improved quality of life.

If you really want to live longer, then start with your attitude. Your way of thinking not only improves your outlook on life, but also how long you actually live. In 2002, researchers at the Mayo Clinic in Rochester, Minn., found that optimistic people decreased their risk of early death by 50% compared with those who leaned more toward pessimism.

"The exact mechanism of how personality acts as a risk factor for early death or poorer health is unclear," says Dr. Toshihiko Maruta, the main investigator in the study. Most likely, it has to do with the fact that pessimists have an increased chance for future problems with their physical health, career achievements and emotional stress--particularly depression. "Yet another possibility could be more directly biological, like changes in the immune system," Maruta adds.

Besides looking through rosier-colored glasses, there other personality traits that can help us live longer, healthier lives. According to Dr. Howard Friedman, a psychologist at the University of California, Riverside, conscientiousness is related to mortality in a significant way. The Terman Life-Cycle Study, which ran from 1921 to 1991, examined an array of factors like personality, habits, social relations, education, physical activities and cause of death.

"Those low on adult conscientiousness died sooner," Friedman concluded. Conscientiousness does not mean looking both ways before crossing the street, it means looking both ways when the light turns green so you don't accidentally run down a slow-moving pedestrian. Beyond that, a conscientious person's long-living qualities probably have to do with the fact that they are predisposed to constructively reacting to emotional and social situations, and are more likely to create work and living environments that promote good health.

There are also more traditional practices that the aspiring centenarian can take. People should stop smoking, eat a balanced diet and maintain a healthy weight. While these may sound "nanny-ish," they are factors that cannot be overlooked. This might not sound like much fun, but it's a lot more fun than being dead.