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Aging News for Senior Citizens
Women Age Faster but Live Longer - Is Testosterone
the Cause?
Males allocate resources to intrasexual and intersexual competition
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June 5, 2006 - It has been widely assumed that men
age earlier than women, as evidenced by their higher mortality rates and
shorter average life spans. But three Northern Michigan University
biology professors contend that the opposite is true. They say theory
and data suggest that females begin to exhibit signs of physiological
decline earlier than males, and that higher mortality figures are not
necessarily correlated with the rate at which we age.
In a recent issue of the American Journal of Human
Biology, an article co-authored by Brent Graves, Mac Strand and Alec
Lindsay presents a novel interpretation of how selection interacts with
cultural and environmental factors to account for gender differences in
the aging process.
Because death can be caused by numerous factors,
higher mortality rates dont necessarily indicate that men age faster,
Graves said.
He added that the physiological evidence to the
contrary includes the tendency for women to suffer vision loss more
rapidly and suffer an earlier decline in their general health status.
Another major factor is that they lose their reproductive capability at
a younger age.
While men may die earlier on average, much of the
difference in mortality rates is due to factors other than physiological
decline caused by the aging process, Graves said.
It is common for females to invest considerable
resources in offspring production, for example, while males allocate
considerable resources to intrasexual and intersexual competition for
mates.
Males engage in more risk-taking behaviors, which
are reflected in much higher death rates three times those of females
in the 15-25-year age group due to accidents and violence. There is
also the physiological cost of testosterone, which suppresses the immune
system and results in higher death rates among males due to infectious
diseases and cancer." he said.
During the evolutionary history of our species,
few individuals lived long enough to express genes that cause
physiological deterioration late in life, so those genes had little
effect on fitness and there was little natural selection to remove them.
But as these late-acting genes accumulate, aging evolves. Getting old,
falling apart and dying is not an adaptive trait. It evolves because of
a lack of natural selection, added Graves.
Graves said the new interpretation came from
applying his training in evolutionary theory to an issue that had been
considered from the perspectives of sociology and gerontology.
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