In 1966, William Hamilton, a British evolutionary biologist, worked out the mathematics describing the "wall of death." Since then, the most popular explanation for why humans don't die by age 55 has been termed the "grandmother hypothesis," which suggests that women enhance the survival of their children and grandchildren by living long enough to care for them and "increasing the success of their genes," Puleston said. However, Hamilton's work has been difficult to express as a mathematical and genetic argument explaining why people live into old age.
Unlike previous research on human reproduction, this study-for the first time-includes data on males, a tweak that allowed the researchers to begin answering the "wall of death" question by matching it to human mortality patterns. According to Puleston, earlier studies looked only at women, because scientists can reproduce good datasets for humans entirely based on information related to female fertility and survival rates.
"People don't like to do two-sex models because [it's difficult] to look at how [men and women] pair up," he said. "But men's fertility is contingent on women's fertility-you have to figure out how they match up. We care about reproduction because that is a currency by which force of selection is counted. If we have not accounted for the entire pattern of reproduction, we may be missing something that's important to evolution."
Men and longevity
In the paper, the researchers analyzed "a general two-sex model
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