A monkey that lives forty years and its relative that dies at ten read the same book of life, but with different notes in the margins. Those notes, identical in all long-lived species and absent in short-lived ones, are what scientists looked for in the genomes of 126 primate species.
To distinguish genuine traces of longevity from random coincidences, the researchers first calculated how long each species "should" live given its body mass. Elephants live longer than mice simply because they are big. But among primates there were overachievers: humans live several times longer than their weight predicts, while some lemurs live noticeably less. Seven long-lived species and six short-lived species became the two teams for comparison.
This does not mean long-lived species are infertile. Rather, evolution tuned their bodies to a more economical reproductive mode: fewer sperm, but more resources for cell repair and protection against aging. This kind of trade-off is called antagonistic pleiotropy, where the same gene helps in youth but harms in old age, or vice versa.
The trace of this trade-off is visible in humans too. We live anomalously long for our size, and our genome carries the same "longevity notes" as other record-holding primates. Perhaps our long life is also the result of an evolutionary bargain in which part of the reproductive energy was redirected to maintaining the body.
If scientists learn to pinpoint exactly which changes in fertility genes extend life, this will open the way to new approaches in the study of aging. But for now this is only a first map of the terrain: to understand how the genes they found work, experiments on cells and animals are needed.
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.