Washington: The last few generations of humans have enjoyed the biggest life expectancy boost in primate history, a new study of mortality patterns in humans, monkeys and apes suggests, according to PTI.
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The gains are partly due to advances in medicine and public health that have increased the odds of survival for human infants and reduced the death toll from childhood illness, researchers said.
Yet males still lag behind females – not just in humans but across the primate family tree, they said. “The male disadvantage has deep evolutionary roots,” said Susan Alberts, biology professor at Duke University in the US.
An international team from the US, Germany, Denmark, Kenya and Canada compiled records of births and deaths for more than a million people worldwide, from the 18th century to the present. The data included people in post-industrial societies such as Sweden and Japan, people born in pre-industrial times, and modern hunter-gatherers, who provide a baseline for how long people might have lived before supermarkets and modern medicine.
The researchers combined these measurements with similar data for six species of wild primates that have been studied continuously for three to five decades, including Verreaux’s sifaka lemurs, muriqui monkeys, capuchins, baboons, chimpanzees and gorillas.
The data confirm a growing body of research suggesting that humans are making more rapid and dramatic gains than ever before seen in the primate family tree. For example, in the last 200 years life expectancy in Sweden has jumped from the mid-30s to over 80, meaning that a baby born today can hope to live more than twice as long as one born in the early 19th century.
The data show that today’s longest-lived human populations have a similar 40- to 50-year advantage over people who live traditional lifestyles, such as the Hadza hunter-gatherers of Tanzania and the Ache people of Paraguay.
In contrast, these modern hunter-gatherers – the best lens we have into the lives of early humans – live on average just 10 to 20 years longer than wild primates such as muriquis or chimpanzees, from which human ancestors diverged millions of years ago.
One indicator of healthcare improvement is infant mortality, which strikes fewer than three in 1000 babies born in Sweden or Japan today. However, it was more than 40 times higher for those born two centuries ago, and is still high among hunter-gatherers and wild primates.
The researchers also studied lifespan equality, a measure similar to income equality that indicates whether longevity is distributed evenly across society, or only enjoyed by a few.
They found that, for both humans and wild primates, every gain in average lifespan is accompanied by a gain in lifespan equality.
Researchers were surprised to find that the longevity of human males has yet to catch up with females, and the improvements in males are not spread as evenly. The life expectancy gender gap is not just true for humans. Females outlived males in almost every wild primate population they looked at.
“It’s puzzling. If we can make life last so long, why can’t we shrink the male-female gap?” Alberts said. Numerous hypotheses have been proposed. Some pin the blame on genetics. Male primates, who carry only one copy of the X chromosome compared with two copies in females, lack a second X chromosome to compensate for any harmful gene variants their single X may have.
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Another possibility, Alberts said, is that gender differences in risky behaviours like fighting continue to hold males back, even while deaths from infectious and chronic diseases that impact both sexes have declined. If we can identify the culprit and intervene, she said, we might be able to help men catch up. The study was published in the journal PNAS.