Why do women live longer than men?

In the human species and in many others, members of the female sex live longer. Why is that?

It is common knowledge that women live longer than men. There are more widows than widowers and, in addition, many more women become supercentenarians than men.

Biology has tried to find out why this is so, putting forward several theories to explain, in particular, the different longevity between sexes in the human species and, more generally, extrapolating it to other species.

However, a very recent study has addressed this question, comparing the life expectancy of different mammals and questioning some of these theories. In the following, let's take a look at what is known about why females live longerand what has been seen in other species.

Why do women live longer?

On average, women live longer than men, with a difference of six to eight years more. A very revealing fact about this fact is that of the supercentenarians, that is, people who live more than 110 years, 9 out of 10 are women. In fact, the person who has lived the longest to date was a woman, Jeanne Calment, who lived to 122 years, born in 1875 and died in 1997.

Why women live longer has been the subject of debate in the scientific community.. Much research has tried to explain why this occurs, relating it to both its medical and economic implications, and trying to see what differences in lifestyle would explain this greater longevity in females.

It has been suggested that, given the personality differences between the sexes, women are less daring than men, which would make them less risk-takers. Others have raised the possibility that, as it is women who play more of a caregiving role than men, nature has taken it upon itself to stretch their lifespan to ensure that they get to raise their offspring until they are sufficiently autonomous.

A new study published just this year 2020, conducted by Jean-François Lemaître's group, has tried to find out why this is so, comparing the differences in longevity between men and women and relating it to that of other mammalian species. In general, they have observed that males tend to live shorter livesin at least 60% of the species studiedbut this does not seem to be due to behavioral aspects.

Male mammals live less

As we have seen it is not only the human species in which males live less than females.. In other species, life expectancy between males and females varies greatly, to the detriment of the former.

Lemaître's study investigated about 130 species, ranging from small, domestic sheep to large, imposing elephants. The biggest differences were found in the Australian opossum, lion, moose, killer whale, great kudu and sheep. For example, in the case of the lion, females live twice as long as males.

Are personality differences to blame?

In both scientific and popular knowledge, it is known that males tend to make riskier decisions. males tend to make riskier decisions. This lesser respect for potentially dangerous situations has been related to the extraversion dimension which, according to several studies, males have higher scores than females. This same dimension has been linked to suffering more accidental injuries, which can sometimes be fatal.

Popular culture has echoed this, and it is not difficult to find web pages with the title "why guys live shorter?" or "¿Por qué los tíos viven menos?", pages that usually have an extensive archive with videos of men making really stupid and dangerous decisions.

Extrapolating this to the animal world, especially mammals, one might think that males also live shorter lives, one might think that males also tend to be more extraverted, but also violent, especially in terms of sexual behavior.especially when it comes to sexual behavior. In many animal species, when two males have to compete for a female, they show their strength: they fight with their horns as moose do, they scratch and maim each other as lions do, or kick each other as zebras do. There is physical fighting, there is damage.

However, Lemaître's research seems to indicate that this is not really the culprit. The study reveals that the intensity of sexual selection, whether by fighting or engaging in other risky behaviors, does not appear to be directly modulating the extent of differences in longevity between sexes in the species seen. Rather, the results seem to indicate that it is due to complex interactions between the physiological characteristics of each individual that are dependent on sexual dimorphism. dependent on sexual dimorphism.

In fact, there are species in which females live less, and one of the explanations for this fact is that they have characteristics that are not advantageous for the environment in which they live. In the case of most mammalian species, it would be the males who have physical characteristics that are not beneficial to them.

Longevity in the female sex

Another proposed explanation has to do with energy expenditure, which is different between males and females. Females of many mammalian species tend to be smaller than males, in addition to having fewer distinctive features.

Males, on the other hand, are larger, larger males, on the other hand, as they grow, also develop very striking traits that require a high nutrient intake for them to develop fully, such as to be fully developed, such as horns, hairier fur, more Muscle mass....

This requires a lot of energy, which can be counterproductive if you live in an environment where food is scarce. Males would be more vulnerable to these extreme environmental factors, plus they would have to eat more than females to stay alive. If there is not enough food for its organism, the organism fails.

This has been observed in the case of bighorn sheep, a species that lives in the mountains of Canada and the United States. Raised in captivity, where they are pampered and fed everything they need, there are no significant differences in longevity between males and females.. On the other hand, in the wild, in areas where the winter is particularly harsh, males live much less than females.

Another explanation is that males produce more androgens than females. males produce more androgens than females.. In fact, these hormones are known as male hormones. Androgens modulate the efficiency of the immune system and, when present in high levels, impair the immune response. Thus, males are more prone to diseases and pathogens than females.

Could chromosomes hold the answer?

Another study, conducted by Zoe A. Xirocostas, Susan E. Everingham and Angela T. Moles, compared the lifespan of about 229 species, including birds, insects, and fish, in addition to mammals. This study found several species in which it is the other way around, i.e., males live the longest, and related this to the type of sex chromosomal configuration they have..

Humans and mammals, in general, have X and Y sex chromosomes. Females are XX, while males are XY. However, in birds it is the other way around, and with other letters. Females are ZW, while males are ZZ. This study found evidence that having a pair of the same type of sex chromosomes, i.e. XX and ZZ, offers a longer life expectancy..

Referencias bibliográficas:

• Lemaître, J. F., et al. (2020) Sex differences in adult lifespan and aging rates of mortality across wild mammals. PNAS. doi.org/10.1073/pnas.1911999117.
• Xirocostas, Z. A., Everingham, S. E. y Moles, A. T. (2020). The sex with the reduced sex chromosome dies earlier: a comparison across the tree of life. Biology letters, 16(3) : 20190867. http://dx.doi.org/10.1098/rsbl.2019.0867.