It's a known fact for more than two centuries – everywhere in the world, women on average live longer than men.
The main reason for this intriguing phenomenon has long eluded scientific explanation, but an international team of researchers now claims to have put an end to the debate.
They report that this occurs mainly, but not only, due to something called the "heterogamete sex theory."
Men are known as the "heterogametic sex" because their sex chromosomes do not match - they have an X and a Y.
This puts them at a disadvantage compared to women, who have two X chromosomes.
Because of their XY chromosomes, males are more prone to harmful genetic mutations and diseases – and consequently, to an earlier death on average.
“We believe that heterogametic sex is partly the answer,” Dr. Fernando Colchero, author of the study at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, told the Daily Mail.
"We found that there are also factors closely related to our evolutionary history that contribute as well."
Since the 1740s, it has been known that women live longer than men on average – a consistent pattern across almost all countries and historical periods.
Currently, global life expectancy averages 73.8 years for women and 68.4 years for men, according to Our World in Data.
Although the numbers have changed over the years, women have always had the upper hand.
This trend is also observed outside our own species, in some of our closest relatives in the animal kingdom.
Female mammals, such as baboons and gorillas, also typically live longer than males, according to the international team of experts.
However, in other classes of animals the opposite happens.
For example, in many birds, insects, and reptiles, males are the ones who live longer, which complicates the picture somewhat.
To find the cause of this gap in lifespan, researchers analyzed data from 528 mammal species and 648 bird species in zoos around the world.
As in humans, 72% of mammals showed a female lifespan advantage, while 68% of birds showed a male advantage.
As the main explanation for this pattern in mammals, researchers emphasize the heterogametic sex hypothesis.
Research suggests that having two X chromosomes protects females from harmful mutations, giving them a survival advantage.
Unlike women, men do not have a second X chromosome to compensate for a harmful “allele” (a variant of a genetic sequence in a particular region of the chromosome).
“Simply put, if you have two copies of the same gene, it's better than just one,” Dr. Johanna Stärk from the Max Planck Institute for Evolutionary Anthropology told the Daily Mail.
She added that it is also possible that the Y chromosome often contains long stretches of repetitive DNA that could be harmful.
The team acknowledges that there are other, smaller factors that explain why female mammals live longer than males.
First, they mention “sexual selection” – the ability to secure a mate at the expense of competition.
In the animal world, males have evolved to develop visible characteristics that attract females, such as larger body size, colorful feathers, or "weapons" like large horns.
Although these traits increase reproductive success, researchers think they shorten lifespan.
“In theory, they are very costly to produce and maintain, while also being associated with males being more likely to fight to monopolize females,” Dr. Colchero told the Daily Mail.
Third, the team thinks this may also be related to parental care.
Researchers found evidence that the sex that invests more in raising offspring tends to live longer.
Female mammals – usually the primary caregivers – likely evolved to survive until their offspring become independent or reach sexual maturity.
An early idea was that environmental pressures such as predators, pathogens and harsh climate conditions were responsible for these gender gaps – but the new study found little support for this.
The researchers used zoo populations to test this idea, where these pressures are largely absent, but found that differences in lifespan persisted even in these protected conditions.
Comparing wild and zoo populations, they found that the gap was often smaller in zoos, but rarely disappeared completely.
Overall, the new study published in the journal Science Advances shows that gender differences in lifespan are deeply rooted in genetics and evolutionary processes.
Gender differences are not just a product of the environment, but part of our evolutionary history – and are likely to continue to exist in the future.
However, Dr. Colchero says it is likely that social and behavioral factors, which were not taken into account in this study, also play a role.
Men and women really are wired differently: Brain scans show noticeable differences between the sexes
If you've ever had an argument with the opposite sex, you may have thought that men and women are simply not on the same wavelength.
Now, a study not only suggests that this is true, but also that men and women are wired differently from birth.
In one of the largest studies on the anatomy of the brain of newborns, scientists performed head scans on more than 500 babies.
Overall, female babies had more gray matter in their brains, while male babies had more white matter.
Gray matter is located mainly in the outermost layer of the brain, the cortex, and plays a major role in mental functions such as memory, emotions, and information processing.
Meanwhile, white matter, the lighter tissue in the center of the brain, speeds up signals between cells and plays a critical role in helping the body process information.
Researchers from the University of Cambridge suggest that these sex-based differences persist into adulthood. /GazetaExpress/
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