It’s all known that women live longer than men. There are more widowers than widowers, and there are many more women who become super centennial than men.
Biology has tried to figure out why of all this, raising several theories to explain, in a particular way, the different longevity between the sexes in the human species and, more generally, extrapolating it to other species.
However, a very recent study has addressed this issue, comparing different mammals’ life expectancy and questioning some of these theories. Next, let’s see what is known about why women live longer, and 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 more years. A pretty telling fact about this fact is that of the supercentenarian, people who live more than 110 years, 9 out of 10 are women. In fact, the person who has lived the most to date was Jeanne Calment, reaching the age of 122, born in 1875 and died in 1997.
Why women live, the most has been a topic of debate in the scientific community. Much has been the research that has tried to explain why this happens, related 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 raised that, given the differences in personality between the two sexes, women are less daring than men, which would make them take fewer risks. Others have raised the possibility that being those who play a role more as caregivers than men, nature has been tasked with stretching their lives to ensure that they grow their offspring until they are sufficiently autonomous.
A new study published, e.g. this year 2020, conducted by Jean-Francois Lemaétre’s group, has sought to find out why this, comparing the differences in longevity between men and women and linking it with that of other mammalian species. In general, they have observed that males tend to live less than 60% of the species studied, but this does not appear because of behavioural aspects.
Male mammals live less.
As we have seen, it is not only the human species in which men live less than women. In other species the life expectancy between males and females varies greatly, going to the detriment of the former.
The lemaétre study investigated nearly 130 species, ranging from small, domestic sheep to large, imposing elephants. The biggest differences have been found in the Australian possum, lion, moose, killer orca, large kudu and sheep. For example, in the case of the lion, females live twice as long as males.
Is it her fault for personality differences?
Both scientific and popular knowledge known that men tend to make riskier decisions. This lower respect to potentially dangerous situations has been related to the extraversion dimension that, according to several studies, men have higher scores than women. This same dimension has been linked to more accidental injuries, which can sometimes be fatal.
Popular culture has echoed this. It’s not hard to find websites with the title “why guys live shorter?” or “Why do guys live less?” pages that usually have an extensive Heterotheca with videos of men making foolish and dangerous decisions.
Extrapolating it with the animal world, especially with mammals, you might think that males also tend to be more extraverted and violent, especially in terms of sexual behaviour. When two males have to compete for a female in many animal species, they show strength: they fight with their horns as elks do, scratch and maim like lions do or kick themselves as zebras do. There’s a physical fight; there’s damage.
However, the investigation of Lemaétre seems to indicate that this is not really to blame. The study reveals that the intensity of sexual selection, either through fighting or taking other risky behaviours, does not appear to be directly modulating the extent of differences in longevity between the sexes in the species seen. The results indicate that it is due rather too complex interactions between each individual’s physiological characteristics dependent on sexual dimorphism.
In fact, there are species in which females live the least, and one of the explanations to this fact is that they have characteristics that are not advantageous to them for the environment in which they have lived. In most mammal species, it would be males who have physical characteristics that are not beneficial to them.
Longevity in the female sex
Another of the proposed explanations have to see the energy expenditure, which is different between males and females. Females of many mammal species tend to be smaller than males and have fewer distinctive features.
In contrast, when they grow up, larger males also develop very striking traits that require high consumption of nutrients to develop fully, 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 and eat more than females to stay alive. If there is not enough food for your body, the body fails.
This has been observed with maroon sheep, a species that inhabits 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 males and females’ longevity. In contrast, in the wild, in areas where winter is especially raw, males live much less than females.
Another explanation shuffled is that males produce more androgens than females. In fact, these hormones are known as male hormones. Androgens modulate the immune system’s efficiency and, when presented at high levels, impair the immune response. Thus, males are more prone to disease and pathogens than females.
Could chromosomes have the answer?
Another study, conducted by Zoe A. Xirocostas, Susan E. Everingham and Angela T. Moles, compared the life expectancy of nearly 229 species, including birds, insects and fish, in addition to mammals. This study found several species in which it happens backwards, i.e. males are the ones who live the most, and related it to the type of sexual chromosomal configuration they present.
Humans and mammals generally have X and Y sex chromosomes. Females are XX, while males are XY. However, in birds, it happens 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 greater life expectancy.