Among mammals, females are usually longer than males, but the reason for scieists has always been questionable. Researchers who examined the data of the zoo animals found that the determining factor is not only genetics, but that the mating pressures also play a significa role. Sexual choice (a process that leads to characteristics in one of the two sexes and increases its chances of absorbing placea) is an importa factor in average life expectancy, so that species that have less pressure for mating experience longer life.
Although humans live more than ever before, women almost always have a higher life expectancy than men, and this is not limited to humans only. In most mammal species, life span is usually beneficial to the material, and in some cases, females are about 2 % longer than males. However, in many species of birds, insects and reptiles, this pattern is observed, in which males usually have a longer life than females.
The reason for this difference may lie in genetics. It is thought that the presence of two X chromosomes in female mammals that causes their monogametic can provide a protection against harmful genetic mutations; While heterogametic males, which have only one X chromosome and one Y, they do not have such advaage. This is the opposite in birds, because males are monosio and females are heteroziguts.
But genetics alone cannot explain the advaage of female mammals (and male birds). To study other effective factors, an iernational group of researchers led by Johanna Stärk of the Max Planck Evolutionary Ahropology Institute in Leipzig, studied factors that could extend or reduce male and female life. Data obtained from zoo records about more than a thousand species of birds and mammals supported the hypothesis called “heterozigut sex” and wild species data showed the same pattern. However, this hypothesis could not yet explain exceptions such as the longer life of female huing birds than males.
What was known was that sexual choice could determine which sex would be longer. One of the sexes may spend a large portion of its energy and biological resources to grow and maiain the features that give her superior to mating, and this can ultimately reduce her life. It is also likely that the reproductive process itself will reduce the lifespan in one of the sexes. The physiological pressures caused by pregnancy, childbirth or eggs and child care can reduce the survival rate, although this effect is not evide in the average life expectancy of human women. The Stark team focused mostly on the data of the garden populations, as the animals do not face environmeal risks such as huers, illnesses, injuries or hunger.
A study published in the journal Science Advances reads: “Species usually have a longer life in zoos than in nature, and many resources associated with the reproductive process can reduce the biological costs of growth and regeneration for each person. For example, the dual -sexual impact of the body size on the survival in males is usually lower, and the individual cost of reproductive production in the zoos does not affect the survival of females. “
Under the conditions of the zoo, female mammals had an average of 5 % longer than males, while this advaage for male birds was about 2 %. Surprisingly, male birds in the natural environme averaged 5 times more than their zoo fellow, and female mammals were 3.5 times more in wildlife than in the wild. However, some mammals were excluded from this rule; About 2 perce of mammal males lived in the zoo and 2 perce in nature more than females, and the same ratio was seen among birds, with about 2 perce of bird females in the garden and just more than 2 perce in nature than males. Life excellence was more common among grasslands such as blue horses, rhinos, deer and zebra, while males were somewhat superior to the carnivorous mammals.
Monochor and multipurpose can also play a role in determining life. Multiple species males usually experience fierce competition to find pairs. As a result, larger size or properties such as stronger teeth and forks may be effective in absorbing females, but these properties require high consumption of energy and biological resources and can reduce life. In corast, birds are more likely to be monopolized than mammals, and as a result, species of sexual dimorphism are diminished and do not require high -end mating displays, usually longer.
However, there are exceptions. Paradise bird males have colorful feathers and joi mating dances and most of their species are multitude; Factors that probably diminish their lives. However, among the birds, males generally live longer, while among the mammals, this is a superiority of those females.
“Our findings can explain why the average life expectancy difference between men and women has remained so stable,” Johanna Stark said. In particular, the longer female life span is also seen among chimpanzees and gorillas, and this shows that the superiority of life span among females is a feature that has been rooted in the deep history of our evolution. “
