Khaberni - Women live longer than men around the world, and this rule applies throughout history and in most human societies. Although progress in medical sciences and living standards has contributed to narrowing the age gap between genders in some parts of the world, researchers believe this rule is not likely to disappear soon, citing its deep-seated connection with evolutionary processes and clearly manifesting in many animal species.
A research team led by scientists from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, conducted an extensive study involving experts from around the world. It explored age differences between males and females among animals, birds, and even reptiles, shedding new light on one of the oldest puzzles in biology: why the aging process and lifespan vary between sexes. The study, published in the scientific journal Science Advances, found that in most mammal species, females live longer than males, citing examples like baboons and gorillas where females typically outlive their male counterparts.
They found that one assumption to explain this phenomenon from a genetic standpoint is the "Heterogametic Sex Hypothesis," which focuses on sex chromosome differences between the two sexes. They explained that in mammals, females have two X chromosomes while males have one X and one Y chromosome, and studies assume that having two X chromosomes in females may provide them with greater immunity against harmful genetic mutations, thereby contributing to their longer lifespan.
The study also found that this rule does not apply universally to all life forms, as males of many bird and reptile species and insects live longer than their females. The researchers relied on data on more than 1,176 species of birds and mammals in zoos around the world, and their data analysis confirmed the validity of the "Heterogametic Sex Hypothesis." They discovered that in most mammal species (72%), female lifespans exceed those of males by an average of 12%, whereas, in most bird species (68%), males live longer than females by an average of 5%.
The head of the research team, Johanna Stark, says, "Some species deviate from the expected pattern of lifespan differences between males and females," and she explained in statements reported by the website "Scitech Daily" that "for many raptor bird species, females are larger and live longer than males, and therefore sex chromosomes between the species are perhaps just part of the story, not the whole narrative."
Researchers believe that reproductive strategies may also play a role in lifespan differences between males and females. According to the rule of sexual selection, males possess specific characteristics to attract females, such as bright feather colors, large body size, and some natural weapons like claws or horns, which increase their ability to attract a mate but also reduce their lifespans.
The new study supports this hypothesis, showing that in animal species where the male mates with more than one female and witnesses competition among males for mating, males usually die before females. In contrast, in most bird species, where the male mates with only one female, thus experiencing less competitive pressure for mating, the male birds' lifespan tends to be longer.
The researchers also found that parental care may also be a reason for longer life, discovering evidence that the species investing more time and effort in childcare, typically females in most mammal species, live longer than the other sex. This trait is considered one of the advantages that nature has granted females in long-lived mammal species like primates, as females live long enough for the offspring to become sexually mature and self-reliant.
Among the hypotheses that the research team tested for validity is the idea that life pressures such as predation, disease, and harsh weather conditions cause shorter lifespans in males compared to females. Researchers compared the lifespans of animal species living in the wild with their counterparts in zoos, but found that the same age gap between males and females remains even under the protective conditions of zoos.
However, they noted that this gap narrows among animals living in captivity, reflecting the same situation in humans, where improved living conditions and access to healthcare contribute to reducing the gender age gap, but does not eliminate it completely.
Researchers concluded that improvements in environmental factors could help narrow the age gap between males and females, but it will not entirely end it. The difference in lifespan between genders is part of the evolutionary history of humans and animals in general, and this difference is likely to continue in the future without change.
