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The Chicago team then compared that data against draft card information for a randomly selected group of American men who were also born in 1887 but who did not reach 100.

Some surprising findings emerged. First of all, a man's chances of reaching 100 rose along with the number of children he had produced by age 30.

Compared to childless men of the same age, a 30-year-old man in 1917 who had one to three children had a 61 percent increased chance of living past a century, the data showed. However, a man's chances for extreme longevity almost tripled if he had fathered four or more children by age 30, the study found.

That's at odds with a prevailing theory in longevity research that holds that "there is a trade-off between the number of children and [parental] longevity," noted Arnold Mitnitski, a longevity researcher and associate professor of medicine, mathematics and statistics at Dalhousie University in Halifax, Canada.

He described the study as "very well-done, very clean."

Theoretically, a household full of young kids should deplete a family's resources and undermine the longevity of parents, Mitnitski said. And yet, young dads with many children lived much longer than other men in this sample.

"This may be due to the support by the children when the person becomes older," Gavrilov speculated. Alternatively, siring many children "could be an indicator of good general health and attractiveness on the marriage market, leading to earlier marriage and hence to more kids by age 30," he said.

In other words, the same robust health that boosted a man's marriage prospects and fertility might also promote long life, Gavrilov reasoned.

Another finding, replicated in prior studies, was that being a farmer (as listed on the Draft Card) more than doubled a man's o
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