WHY DO WOMEN OUTLIVE MEN?

Despite recent advances in health, the average newborn boy still can expect a much shorter life than the average newborn girl.

U.S. life expectancy is currently about 79 for females, 71 for males. And there's no sign the gap will close.Why do women outlive men? Because "they deserve it," quips Estelle Ramey, a retired professor of physiology and biophysics at Georgetown University and an expert on sex differences.

"Mother Nature is a radical feminist," Ms. Ramey suggests, only slightly more seriously. Males are born virtually programmed by biology as well as culture, she believes, for a shorter life than women.

For starters, men carry two different sex chromosomes, known as an X and a Y. By carrying two X chromosomes, women can offset a defective one, probably the major reason males are much more prone to birth defects and genetic diseases.

Since the X chromosome carries genes vital to the immune system, women also may resist infectious diseases better than men, Ms. Ramey said in an interview.

"But the big killer is heart disease," she noted. There, too, men are at a critical disadvantage in today's world.

Males secrete far more of the sex hormone testosterone than females. The hormone promotes blood clotting - useful when a hunter is gored by his prey, but less so against the more likely threat of an internal blood clot next to the heart.

The same hormone also promotes production of the low-density lipoproteins, the "bad cholesterol" that helps deliver high-calorie fat to hard-working muscles but also constricts blood vessels.

Testosterone promotes secretion of stress hormones that cause men to react more quickly and intensely to stress than women do. This "fight or flight" stress response sharply elevates blood pressure whenever a man flies off the handle.

"The issue isn't hard work - that's good for you," Ms. Ramey said. "The issue is how men react when they have no control over a situation, when your boss reams you, or the highway is a parking lot and there's someplace you're supposed to be."

The result can be blood vessel damage that after about age 25 never completely heals. This damage alone, scientists are concluding, is a major risk factor for heart attacks and strokes.

On top of all this, Ms. Ramey adds, "society reinforces biology" by encouraging aggression and risk-taking. Males die far more often than females from accidents, suicides and homicides.

Men's greater smoking prevalence also contributes to the life-expectancy gap.