NEW YORK The biologist Benjamin Mayne has attracted a lot of media attention with his research, which shows that peoples natural life expectancy is 38 years. If hes right, the impact is huge for starters, wed have to rethink our entire healthcare system. This system is based on the (possibly unrealistic) assumption that deaths that are not the result of accidents or violence can be attributed to illnesses and that all illnesses can be overcome with adequate medical research.

What if instead we are programmed to die before we are old enough for a midlife crisis?

Not so fast. The 38-year limit stems from a system that Mayne and his colleagues developed to apply to vertebrates, from the living, fast-dying young newt (2.1 years) to the slow-moving Greenland shark (400 years).

The researchers calibrated their aging clock based on animals that were kept in captivity and whose maximum lifespan is recorded in a database. Humans have a maximum life expectancy of around 120 years, but this has been excluded from their calibration data because it is too big an outlier. According to the article published in Nature Scientific Reports, this does not reflect the variability (of) the actual global average lifespan (60.9 to 86.3 years).

So if we have a record of 120 and a true global average of 61 to 86, how could we have a natural lifespan of 38? In some ways, this number makes sense since our closest relative, the chimpanzee, is 37 years old. Still, it doesnt fit observations. Captive chimpanzees with good health care will never live to be 80 or more years old while humans do it routinely long before there was anything like modern medicine.

Socrates was 70 years old when he died and was still so vigorous that his enemies had to poison him. Benjamin Franklin, who pointed out that 18th century medicine does more harm than good, managed to live 84 years. Historical records show that human aging has been at the same pace for 2000 years.

People sometimes confuse death from age with life expectancy, which has been quite low for a very long time. Keep in mind that life expectancy is average and has included a disproportionate number of infants for centuries. Before modern medicine, infants and children often died from infections, malnutrition, or birth defects, and newborns and young women died from birth complications. Life expectancy was only 46 years in 1907, but that was because children died routinely not because someone died at the age of 46. People who survived the dangers of childhood were more likely to reach maturity.

And modern life seems to be a murderer as well as a savior. The diseases that kill most people over 55 are heart disease and cancer, which we have learned would be less common if people got more exercise, avoided cigarettes, and ate less processed foods, sugar, and high fructose corn syrup , Even agriculture appears to have been a mixed blessing: medical archaeologists have found that elderly people from farming societies were shorter compared to their ancestors and were more often sick or malnourished.

Mayne, who works for the Commonwealth Scientific and Industrial Research Organization in Australia, says his system is based on a well-known aging marker called DNA methylation a change in the material that glows on your DNA. It has no effect on the actual code, although it affects how the code is read and expressed.

Over time, our cells accumulate methylation as our arteries take up plaque or our teeth start to rot. DNA from different species varies in the number of sites susceptible to methylation the more sites, the faster the aging clock ticks. In addition, Mayne explains, the animals aging clocks are tied to their reproductive clocks. They are usually long-lived animals that reproduce slowly and are more susceptible to extinction.

I directed this from S. Jay Olshansky, an aging expert at the University of Chicago. He says it is important to understand that we are not programmed to die at a certain age. Our selfish genes are under evolutionary pressure to maximize their own reproduction. This means that you have been programmed so long that you can take care of your offspring until they are reasonably self-sufficient. After that, nature becomes indifferent and you are left to the moody devastation of entropy. If you are lucky and take good care of yourself, you can idle for a few decades afterwards.

The slower an animals reproductive cycle, the longer it takes for this roll-out phase to begin. If you are a mouse or a wood mouse surrounded by predators, natural selection favors those who reproduce early within a month of birth. A tough animal like the Greenland shark can afford to postpone the birth until around 150 years.

People are getting out of hand by 50 CDC data shows that degenerative diseases occur less or more frequently from this point on, but when this phase begins for us is not clear. Olshansky is not crazy to conclude that the rollout phase could begin around the age of 38.

Health care is a way to help those who lose in this lottery. It is also a way to alleviate the suffering that can last for years in people with degenerative diseases.

Because age is a risk factor for so many terrible diseases and we cant stop quitting smoking, scientists should continue to understand how aging works and whether there is a way to slow it down. And this is exactly where these long-lived, slowly reproducing animals can teach us something.

Science writer Faye Flam is a Bloomberg Opinion columnist.

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No, we do not have a natural lifespan of 38 years - gotech daily