Throughout human history, men’s lives have been shorter than women’s. On average, live 5.4 years longer than their male counterparts. To finally uncover the reasons behind this phenomenon, a team of researchers from the Max Planck Institute for Evolutionary Anthropology in Germany turned to our animal relatives for clues.
During their study, the scientists examined over 1,000 species of fauna to identify common evolutionary traits among species where one sex lives longer than the other.
Humans are not the only species where females tend to outlive males. In 72 percent of , females live on average 12 percent longer than males. For instance, female moose can live more than twice as long as males.
Meanwhile, in birds, males generally outlive females, averaging 5 percent longer in most species (68%).
Key Factors: Genetics, Polygamy, and Child Rearing
According to the team’s findings, one of the main explanations lies in our chromosomes, a fundamental difference between the sexes. In mammals, females have two X chromosomes, while males have one X and one Y chromosome.
Lead researcher Johanna Sterck told BBC’s Science Focus that since men have only one X chromosome, any harmful mutations on it can have significant effects. If there were a second X chromosome, it could likely compensate for these impacts. Meanwhile, women are better protected from undesirable genetic mutations thanks to their second X chromosome.
Dr. Sterck also noted, “There is a so-called ‘toxic Y chromosome’ hypothesis; it suggests that the Y chromosome may carry genetic elements that adversely affect health.”
In contrast, in , the situation is reversed. Females have two different chromosomes: ZW, while males have two identical ones: ZZ. However, not all bird species have males living longer.
“Some species have shown a pattern contrary to what we expected. For example, in many raptors, females are larger and live longer than males. Thus, sex chromosomes may only be part of the story,” Ms. Sterck pointed out.
Another important factor is reproductive strategies. According to the scientist, males often pay a high price for reproduction: “To find a mate, they expend energy fighting rivals, which increases the risk of injury and shortens lifespan.”
The researchers noted that in terms of finding a partner, male birds are generally monogamous, while a very small percentage of male mammals settle for one partner.
While the most attractive and strongest male may produce more offspring, the biological resources spent on developing muscles or antlers negatively impact lifespan.
In monogamous species, competition is less fierce, resulting in a minor difference in lifespan between males and females.
The next factor influencing for both men and women is child-rearing. One might expect that the sex responsible for raising children would pay for it with a shorter life. But the opposite is true.
“We found the opposite: individuals who care for often live longer. This is especially true for primates, whose young remain dependent on their mothers for a long time,” Ms. Sterck explained.
For example, baby can stay with their mothers for up to 10 years. Therefore, the longer a mother lives, the longer she can care for her offspring. A female’s long life can ensure that she sees her child reach maturity.
The study’s findings were published in the journal Science Advances.
Photo: Unsplash
