Theory on why women live longer than men

Why Do Women Tend To Live Longer Than Men? ScienceDaily 2/8/07

In short: "Because the mitochondrial genome (as well as the X chromosome) is inherited from the mother, evolutionary pressures might have selected for versions optimized for the female body. If the mitochondrial genome is better adapted to the female environment, the mitochondria in females just may work better, and longer, than those in males. "

A bit more:
"A provocative new model proposed by molecular biologist John Tower of the University of Southern California...genes known to increase longevity always affect male and female flies differently...a gene for the antioxidant enzyme Cu/Zn-superoxide dismutase (SOD) led to a longer life span in male flies, but had a less dramatic impact in females...a new way to link the regulation of life span to the biological mechanisms that trigger a fertilized egg's development into a male or female. The model suggests that sexual differentiation may exact a high biological cost -- reduced function of the cell's mitochondria, the energy-producing components of the cell...In recent years, much of Tower's research on aging has focused on extending life span by manipulating genes that produce the cell's most powerful and ancient antioxidants -- the superoxidase dismutase (SOD) enzymes. Antioxidants protect cells from the toxic effects of oxygen free radicals, which are produced when cells burn their oxygen fuel during normal metabolism. Free radicals are destructive to DNA, protein and the other complex, delicate molecules that carry out life's every function. In the so-called "oxidative stress" theory of aging, biologists surmise that the whips and scorns of time -- arthritis, dementia, cancer and all the rest -- are caused in part by a steady accumulation of such damage...The mitochondria, thousands of which populate every cell, are the body's largest producers of free radicals. The mitochondria also are unique in that they evolved from free-living bacteria and contain their own complete set of genes, or genome, which has remained distinct from the cell's genome (stored in the nucleus) over millions of years of evolution. While both parents contribute to their offspring's cellular genetic inheritance, only the female passes on the mitochondrial genome to the next generation. Why, and how, this asymmetrical inheritance happens is not clear, but Tower thinks understanding it may be key to understanding sex differences in aging...Because the mitochondrial genome (as well as the X chromosome) is inherited from the mother, evolutionary pressures might have selected for versions optimized for the female body. If the mitochondrial genome is better adapted to the female environment, the mitochondria in females just may work better, and longer, than those in males. ...Mitochondria play a key role in regulating the programmed cell death pathway, or apoptosis. In flies and humans, apoptosis works during normal embryonic development and sexual differentiation, sculpting the body by killing unwanted cells. But the cell death pathway, in which the p53 gene is a central player, also appears to malfunction more frequently over an organism's lifetime, thereby contributing to aging and aging-related diseases like Parkinson's. This might happen more often or differently in males, Tower speculates, leading to a shorter life span"

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