New Research Explains Why Females Have a Longer Lifespan Than Males

New research that analyzes the lifespan in wild mammals shows that females live basically longer than males. The study says that, on average, females live 18.6 percent longer than males from the same species.

This is much greater than the well-analyzed variety between men and women, which is about eight percent. The researchers say the differences in these other species are caused by a mix of sex-specific characterizations and local environmental components.

Females Live Longer on Average

In every human population, women live longer than men; therefore, nine out of ten people who live to be 110 years old are female. This paradigm, as per scientists, has been stable since the first detailed birth records begun in the 18th Century.

Although the same premise has been held about animal species, widespread information on mammals in the wild has been little. Now, an international team of experts has analyzed age-specific mortality rates for a large-scale, diverse group of 101 species. In 60 percent of the observed species, the researchers discovered that females lived longer than the males; on average, they had a lifespan of 18.6 percent longer than males.

“The magnitude of lifespan and aging across species is probably an interaction between environmental conditions and sex-specific genetic variations,” said lead author Dr. Jean-Francois Lemaître, from the University of Lyon, France.

He offers the instance of bighorn sheep for which the team has access to relevant data on various populations. Where natural resources were steadily available, there was a small difference in lifespan. Still, in one region where winters were especially harsh, the males lived much shorter lives.

“Male bighorn sheep use lots of resources towards sexual competition, towards the growth of a large body mass, and they might be more sensitive to environmental conditions,” said Dr. Lemaître. “So clearly the magnitude of the difference in lifespan is due to the interaction of these sex-specific genetics, the fact that males devote more resources towards specific functions compared with females, and to the local environmental conditions.”

Chromosomes are the Key

Although females lived longer than males, the researchers determined that it did not mean that the threat of dying is enhancing more in males than females as they get older. The anticipated male mortality is always greater, but the ratio of mortality is approximately similar in both genders as they age.

Recent research on this matter implied that the genetic variations between males and females were significant. In humans, our cells are filled with various chromosomes, relying on the gender. Females have two X chromosomes, and males have an X and Y chromosomes. The hypothesis is that the additional X in women has a defensive effect against dangerous mutations and that this is also seen in other species.

The author of the new research on mammals explained that both these studies are complementary.

“They show that in XX or XY systems, the XX, or the female, lives longer, so clearly there is an effect of sex chromosomes,” said Dr. Lemaître. “What we show in our paper is that the difference is very variable across species, meaning there are other factors that need to be considered to explain this variability.”

The paper has been published in the journal Proceedings of the National Academy of Sciences.

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