Take two similar monkeys, and one may live four times longer than the other. The secret isn't just body size. It's hidden in the genes, like notes scribbled in the same book that change the meaning of what you read.
Scientists found such "notes" in seven species of monkeys that live unusually long for their weight, humans included. In all the long-lived ones, the same changes sit in the same spots in the genes, while short-lived species don't have them. Most intriguingly, most of these changes are in genes that govern male fertility.
Humans made the long-lived team too, and we carry the same genetic "notes." Perhaps our long life is the result of an ancient choice evolution made for us: slightly less energy for reproduction, but more for repairing cells. If scientists figure out exactly how these genes work, they could look for ways to slow aging.
Among the 13 selected primate species, humans turned out to be the long-lived outlier: our longevity quotient exceeds 1.3, whereas in some lemurs and guenons it falls below 0.8. That means humans live several times longer than their body mass would lead you to expect.
The idea of a trade-off between reproduction and longevity appears in Aldous Huxley's novel Brave New World, where society sacrifices individual lifespan for stable reproduction. In this paper, that trade-off can be traced at the level of amino acid substitutions in male fertility genes.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.