Life in the Fast Lane

While it may seem highly unfair to their male counterparts, women do live longer than men. Aside from a number of medical conditions, it all boils down to one thing — testosterone, based on studies by researchers in recent years. In testament to an abundance of the hormone, men partake in peacock-like displays of plumage and daredevil, risky behavior in effort to ‘get the girl,’ ultimately increasing their death rates.

One contributor to the gender difference in life span is the influence of sex hormones, according to a study at Harvard University.

The male hormone testosterone increases aggressive and competitive behavior in young men, say researchers Thomas Perls, a geriatrician at Harvard Medical School, and Ruth Fretts, an obstetrician-gynecologist at Harvard-affiliated Beth Israel Deaconess Medical Center in Boston.

Vying for Attention
Males often have to compete for female attention, and vying against other suitors can be risky, according to a study for the University of Michigan by researchers Daniel Kruger, PhD, and Randolph Nesse, MD. They claim that men are much more likely than women to engage in risky and sometimes violent behavior, in effect raising men’s death rate.

More men than women die in car accidents, other types of accidents, homicides, and suicides, they note, adding that in the U.S., the gender gap in death rates peaks in young adulthood which is mainly due to behavior.

Kruger and Nesse don’t claim that all men engage in risky behavior to impress women, but they note that men, particularly those experiencing uncertainty or deprivation “may develop riskier life strategies, leading to higher mortality rates.”

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The male-female gap in death rates may be a sign of male-male competition in a society, they suggest, arguing that the difference in life expectancy stems from the biological imperative of attracting mates.

From body-building and wrestling competitions to the blinged-out hotrod, males compete aggressively for female attention, and that costs them something. In nature, it means riskier physiology and behavior for the males, such as putting more resources into flashy plumage or engaging in physical power struggles.

Modern lifestyles, male behavior and physiology are shortening their lifespan relative to women, and actually exacerbating the gap between male and female life expectancies, Kruger said.

Male physiology, shaped by centuries of sexual competition is placing men at a disadvantage in longevity. And behavioral causes — smoking, reckless driving, violence — set men apart from most women. “Because mortality rates in general are going down, behavioral causes of death are ever more prevalent.” Kruger said.

Human mortality rates examined by socioeconomic status shows that the gender gap is affected by social standing — males in lower socio-economic levels tend to have higher mortality rates than their higher-status peers. The impact of social standing is greater on male mortality than females, Kruger claimed, partially because males who have a relatively lower status or lack a mate engage in a riskier pattern of behaviors in an attempt to get ahead.

Universal Male Mortality
The gap of life expectancies of men and women is actually ancient and universal, according to Kruger and Nesse.

“Women live longer in almost every country, and the sex difference in lifespan has been recognized since at least the mid-18th century.” said Kruger. “It isn’t a recent trend — it originates from our deep evolutionary history.”

“This whole pattern is a result of sexual selection and the roles that males and females play in reproduction.” said Kruger. “Females generally invest more in offspring than males and are more limited in offspring quantity, thus males typically compete with each other to attract and retain female partners.”

This slanted mortality isn’t even unique to our species — the males fall short in common chimps and many other species, Kruger said. The greatest difference in mortality rates between male and female chimps occurs at about 13 years of age, when the males are just entering the breeding scene and competing aggressively for social status and females.

Gender Gap by Age
The mortality gap varies during stages of life.

Gender gap is most pronounced in those who live 100 years or more. Among centenarians worldwide, women outnumber males 9 to 1, according to Perls and Fretts, who studied all centenarians from 8 cities and towns around Boston. Out of 100 people in all, 85 were women.

Between ages 15 and 24 years, men are 4 to 5 times more likely to die than women, a time frame which coincides with the onset of puberty and an increase in reckless and violent behavior in males. Researchers refer to it as a “testosterone storm.”

After age 24, the difference between male and female mortality narrows until late middle age.

In the 55 to 64-year-old range, more men than women die.

The oldest person for which reliable records exist was a woman who recently died in France at the age of 123. “Reaching such an age is like winning the lottery.” Perls said. “The odds are about one in 6 billion. From a practical point of view, we can consider 100 years as the average maximum of human life. We’re not there yet, of course. At present, average life expectancy for those born after 1960 is about 85 years.”

Childbirth
“It seems likely that women have been outliving men for centuries and perhaps longer.” say Perls and Fretts. Even with the sizable risk conferred by childbirth, women have out-survived men at least since the 1500’s. Since the early 1900’s when the death risk for women of childbearing age was as high as that for men, improved health care, particularly in childbirth, has put women ahead of men again in the survival struggle.

“Studies of chimps, gorillas, and other species closely related to humans suggest that a male’s reproductive capacity is actually limited more by access to females than by life span.” says Perls. “And because men have not been involved in child care as much as females, survival of a man’s offspring, and thus his genes, depended not so much on how long he lived, but on how long the mother of his children lived.”

The difference in life expectancy between men and women is maternal mortality, according to Hogue, a professor of maternal and child health and epidemiology at Emory University’s Rollins School of Public Health.

“It’s certainly true that males are much more at risk of violent death and associated with taking risks.” says Hogue. “That may be part of the explanation as to why life expectancy at birth is now better for women than men.”

“The major killer in early life for women was maternal mortality, and that has been tamed considerably, whereas the major killer for men is violence and accidents, and that has not gone down as dramatically as childbirth deaths have gone down.” she adds.

Stupid Stunts

For more information on Kruger visit http://www-personal.umich.edu/~kruger/
For more information on Nesse visit http://www-personal.umich.edu/~nesse/
University of Michigan (2006, May 10) Evolutionary Forces Explain Why Women Live Longer Than Men

Special thanks to Donna for the inspiration by sending these ’safety’ photos.

Related stories:
Men Talk More than Women – New Research
Research Proves Men Talk as Much as Women
Study Finds Men Not So Naughty – Women Not So Noble
The Face – Not the Body – Attracts a Mate

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