A woman in Tokyo practices physical activity with wooden dumbbells. A 72-year-old… (Franck Robichon / EPA )
Modern humans have gotten incomparably good at survival, doing more to extend our lives over the last century than our forebears did in the previous 6.6 million years since we parted evolutionary ways with chimpanzees, according to a new study.
In fact, humans in societies with plentiful food and advanced medicine have surpassed other species used in life-extending medical research in stretching our longevity and reducing our odds of dying at every point along our ever-lengthening life spans, the study finds.
The research, published online Monday by the journal Proceedings of the National Academy of Sciences, touches upon the hotly debated question of whether an upper limit to longevity is inscribed in our genes. It makes clear that life extension begins at birth, with a child born in the last four generations standing a better chance of being alive during infancy, adolescence, the reproductive years and after than in any of the 8,000 human generations that came before.
The study authors, from Germany's Max Planck Institute for Demographic Research, began by comparing people who have lived or now live in primitive hunter-gatherer societies around the globe in which life spans have been well documented with citizens of industrialized countries in Europe and Asia. A typical Swede, for instance, is more than 100 times more likely to survive to the age 15 than a typical hunter-gatherer. And a hunter-gatherer who has reached the ripe old age of 30 is about as likely to die in the following year as the world's champion of longevity — a 72-year-old woman in Japan.
In evolution's actuarial table, the researchers wrote, "72 is the new 30."
The bulk of that progress has been made since 1800, when the average life span of a Swede at birth was 32. That is roughly on a par with the 31 years that the average hunter-gatherer can expect to live today.
By the year 1900, the average life span in Sweden had reached 52, and today it stands at 82 — an increase of more than 150% in just over 200 years.
That puts to shame efforts to extend the lives of laboratory animals, the study authors noted. By inducing genetic mutations in various species, scientists have boosted the longevity of nematode worms by more than 100%, of fruit flies by about 85% and of mice by roughly 50%. Experiments in caloric restriction have also extended the lives of lab animals, but they also fall short of humans' real-world gains.
No species dramatizes the breathtaking rate of humans' life extension more than chimpanzees, mankind's closest relative. At any age, the life expectancy of a human in a hunter-gatherer society is closer to that of a chimp in the wild than it is to a modern-day resident of Japan or Sweden, according to the study.
The authors wrote that the rapid improvements in human survival could only be accounted for by environmental changes, including better nutrition and medical advances; changes in the genome accumulate far too slowly to explain the progress.
"We have much to learn" before divining the limits of the human life span and understanding which forces push hardest against those limits, the authors wrote. The report was overseen by James W. Vaupel, a leading proponent of the idea that human longevity may have no upward limit.
Jakob Bro-Jorgensen, an evolutionary biologist at Britain's University of Liverpool who was not involved in the study, said it "revealed with remarkable clarity the spectacular drop in human mortality that has occurred in some industrialized societies over the past few generations."
Those rapid gains in human survival are clearly due to environmental, not genetic, influences. But by favoring some in human society over others, Bro-Jorgensen ventured, such advances may end up subtly changing the course of human evolution as well.
"Are the people who leave the most descendants under today's radically different living conditions characterized by different genes than those who did so when we were hunter-gatherers?" he asked.
Other experts criticized the study for failing to factor in the fact that obesity and other health problems have started to reduce life expectancy for some people in industrialized societies.
S. Jay Olshansky, a public health professor at the University of Illinois at Chicago and a leading researcher in the emerging field of biodemographics, said the absence of such data — showing, for instance, that the life spans of white Americans who haven't completed high school have fallen significantly since the 1990s — suggests the authors "have a particular bias toward reporting only news that favors a preconceived notion that life expectancy can only rise."