Another View of Gender Differences In Longevity
Via Time: "Another more complicated possibility [for women's longevity] is that women have two X chromosomes, while men have one. (Men have an X and a Y.) When cells go through aging and damage, they have a choice in terms of genes - either on one X chromosome or the other. Consider it this way: you have a population of cells, all aging together. In some cells, the genes on one X chromosome are active; in other cells, by chance, the same set of genes, with different variations, are active on the other X chromosome. Don't forget, we all have the same genes - the reason we differ is because we express different variations of those genes, like different colors of a car. Now, if one set of variations provides a survival advantage for the cells versus another, then the cells with the advantage will persist while the other ones will die off, leaving behind more cells with the genes on the more advantageous X chromosome. So, in women, cells can perhaps be protected by a slightly better variation of a gene on the second X chromosome. Men don't have this luxury and don't get this choice."
Link: http://www.time.com/time/health/article/0,8599,1827162,00.html