A new study confirms that guys are checking out early, leaving researchers stumped.
In a patriarchal world, men have it all—except time.
That's right, y chromosome-havers: The women in your life are still likely to outlast you, says a new study in Proceedings of the National Academy of Sciences.
The international team of researchers assessed birthrates and death rates for six human populations from the 18th century to the present and compared them against similar data for six species of primates. In the aggregate of the 12 populations highlighted, the team found an average female lifespan advantage of approximately two years, says study co-author Susan Albert.
For the six human populations, the research team looked at several conditions associated with lifespan, such as infant mortality rate and lifespan equality, which indicates the distribution of lifespans within one population. For instance, they chose 18th century Sweden because of high lifespans and solid data, and compared it to 21st century Sweden to observe the difference.
They also chose such populations as the Hadza and Aché, mid-20th century hunter-gatherer people from East Africa and the Paraguayan Amazon, respectively, because data on their non-modernized cultures represent the pre-industrialized humans. Though the data is telling, the researchers still can't explain the gender gap.
"Nothing in our data can tell us about why men and women still live such different lifespans," Albert says. "Men today in Europe live way longer than women did in 18th century Sweden, but they still live shorter than [European] women today do."
A great variance, however, exists between the lifespans in the samples. Japanese women, for instance, live more than six years longer than their male counterparts, but Aché men outlast their women by about nine months.
The other four human samples—Hadza people, 19th century Liberians, 18th century and 21st century Swedes—showed serious female lifespan advantages, to the tune of at least three years (save Liberia, which only displayed a six month female advantage).
While the research team can't be sure, Albert offers a few hypotheses to explain the gap. One may have to do with male risk-taking tendencies—fighting to protect the family back in the day, or shotgunning a PBR and jumping off a roof in the present day.
But another, more scientific reason could have to do with the chromosomes themselves: With two X chromosomes, women have a backup in case one of their chromosomes is flawed. A 2006 study titled "Why Women Live Longer Than Men: Sex Differences in Longevity," published in General Medicine, notes that male birds outlast female birds under similar captive conditions. The difference? Female birds have one short and one long sex chromosome, negating the backup chromosome protection found in primates and humans.
Yet the beautiful thing about evolution is that it's not a done deal, Albert adds.
"It's not that evolution happened and then humans happened. Evolution is always happening—it's still happening."