Why Women Outlive Men

Why Women Outlive Men

From a peacock’s showy plumage to a 20-year-old’s blinged-out SUV, males compete aggressively for female attention. But their aggression comes at a price: males of all mammalian species tend to have shorter lifespans than females.

“The sex difference in lifespan has been recognized since at least the mid-18th century,” says Daniel J. Kruger, a research scientist in the University of Michigan School of Public Health and the Institute for Social Research. “Women live longer in almost every country. It originates from our deep evolutionary history.”

Kruger and co-author Randolph Nesse, a professor of psychology and psychiatry and director of the UM Evolution and Human Adaptation Program, believe the difference in life expectancy stems from the biological imperative of attracting mates. Because females generally produce far fewer offspring than males and invest more in those offspring, males typically compete with one another for female partners—and their competition leads to risky physiology and behavior, such as physical sparring.

Modern lifestyles exacerbate the gap between life expectancies. Shaped by eons of sexual competition, male immune systems are somewhat weaker than their female counterparts, and male bodies are less able to process fat. Men are also more vulnerable to behavioral causes of death—smoking, overeating, reckless driving, violence. Kruger notes that males who have a relatively lower status or who lack a mate engage in a riskier pattern of behaviors in an attempt to get ahead.

Kruger and Nesse published their study, “An evolutionary life-history framework for understanding sex differences in human mortality rates,” in the spring 2006 edition of Human Nature.

UM News Service

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