Men are still not living as long as women — and that also applies to humans’ primate cousins, a new study shows.
In the study, researchers looked at the data of six populations of people from both the modern and historical times, in different countries. The researchers found that, “despite the enormous gains in the human lifespan over the past century, the male-female difference is not shrunk,” said Susan Alberts, a professor of biology at Duke University and co-author of the new study.
The researchers found that the extent to which women survived men varied between populations. For example, the largest male-female difference in life expectancy between the studied populations was in present-day Russia, where the gap is about 10 years. Much smaller differences were found in other populations, such as people who live in the modern, Nigeria and India.
In addition, the scientists found that the gap for non-human primates was much smaller than it was for the man.
In the study, the researchers looked at the mortality of six different human populations that represented “the whole of the human experience.” The scientists pulled information about the three generally a long life span, populations of a large international database called the Human Mortality Database, including the Swedish population from 1751 to 1759, the Swedish population from 2000 to 2009, and the Japanese population in 2012.
The researchers have also looked at the data from three populations with generally much shorter life, including two modern hunter-gatherer populations, the Hadza of Tanzania and the Pain of Paraguay, as well as data from a population of freed slaves, who migrated from the united states to Liberia between 1820 and 1843.
For non-human primates, the researchers looked at the data from the six wild populations of sifakas, muriquis, capuchins, gorillas, chimpanzees, and baboons, each with a population somewhere between 400 and 1,500.
Finally, the researchers also supplemented their data on the man by looking at smaller data sets from an additional 16 human populations, including people in Russia, China, India, the united states and other countries.
The study produced three important findings: in the First place, with a long-life populations of humans, such as that of modern Japan and Sweden, the average life span are fairly constant, which means that the age of death within the populations is fairly similar in the different countries: Most deaths in these countries occur when adults are between the late ’70s and early’ 90’s. In contrast to other primates’ life span can be much shorter and highly variable.
Second, the difference in life between the people of the industrial society and that in the hunter-gatherer societies was greater than the difference between hunter-gatherers and non-human primates. People in the industrial society and live 30 to 50 years longer than hunter-gatherers, but the hunter-gatherer life is only 10 to 30 years longer than non-human primates, the researchers found.
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Third, the life of women tend to be more and less variable in length than the lives of the men, the researchers found.
In all populations, the oldest individuals tend to be females, according to the study. However, for both non-human primates and human populations, with shorter life expectancy, the male disadvantage in life span seems to be relatively small.
The reason for this difference between men and women is still not clear, the researchers said. But the existence of such a difference in so many different groups of people, as well as in non-human primates, suggests that the inequality has “deep evolutionary roots,” the researchers wrote in their study.
A possible reason for the difference is that “men take more risks,” Alberts told Live Science. If people’s life spans are cut short by risk-taking behavior, it can explain the gap in life expectancy between men and women, as well as the larger variability in the males of the age of death compared to women, ” she said.
Another possibility is that testosterone plays a role, Alberts said. The higher levels of testosterone found in men may compromise the immune system, which can affect how long they live, ” she said.
The study has a number of limitations, such as relatively small sample of non-human primate populations, the researchers noted.
The research is published today (Nov. 21) in the journal Proceedings of the National Academy of Sciences.
Originally published on Live Science.