Paying more for life insurance? If you're male, you probably are, because the mortality rate, or likelihood of death, is higher for men than for women. And according to an exhaustive new study of gender mortality across centuries and among species, it's all about biology - so forget about lowering that insurance premium.

"Why Men Die Younger," a study published in February 2001 by the Society of Actuaries, concludes that the hormone testosterone "plays havoc biologically and behaviorally with men's bodies," leading to diseases and risk-taking behavior that are more common among men than women. Estrogen, the female hormone, tends to increase longevity for women. The greatest difference between male and female mortality rates occurs at age 22, when testosterone levels for males are traditionally highest.

Testosterone promotes higher blood pressure, the study says, and suppresses the effectiveness of the immune system. It also causes males to engage in risky behavior such as unsafe driving, illegal drug use, and alcohol abuse, all of which are more prevalent among men than women.

"Many have concluded that the male is the weaker or frailer of the sexes," says Barbara Blatt Kalben, the study's author. Over a three-year period, Kalben examined demographic data from as early as the 14th century and concluded that mortality differences are global, but the extent of the difference varies by country. For instance, in the former Soviet Union, women live 13.8 years longer than men. In the United States, however, women outlive men by 5.7 years, down from 7.8 in the mid-1970s.

The study found that men die younger from 66 of 72 causes of death considered, including cancer, diabetes mellitus, heart disease, infections, strokes, and pulmonary disease. Only six causes of death had higher female mortality rates: Alzheimer's disease, asthma, breast cancer, kidney infections, pregnancy/childbirth, and rheumatic fever.

Higher life expectancy among women was traditionally attributed to most women working in the home while men joined the workforce. However, the new study says that working women have lower mortality rates than those who stay at home.

It's not all doom and gloom for men, Kalben says. "The best thing to do is be aware of the risk-taking behavior discussed in the study," Kalben says. "The primary danger is cigarette smoking. There's nothing new here — we already knew that mortality data show male and female smokers live nine years shorter, on average, than nonsmokers. There's other risky behavior that men engage in more frequently, such as driving under the influence and driving without a seat belt."

Kalben says the study can help actuaries, who set the rates for life insurance by examining mortality data, to understand the causes behind mortality rates for men and women. "Actuaries try to predict what will happen in the future," she says. "Years ago the insurance rates were the same between males and females. This helps actuaries understand why females live longer, and get a grasp on what may happen in the future. If you don't know the causes of mortality, it's hard to make a prediction."

Females in nearly every species, including crustaceans, fish, insects, humans, mollusks, primates, and other mammals, are more likely to live longer than males. But if birds wanted life insurance, they'd be in luck: Because of their chromosomes, male birds live just as long as females.