It is common knowledge that women live longer than men. There are more widows than widowers and, furthermore, many more women become supercentenarians than men.
Biology has tried to find out the reason for all this, proposing 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 lifespans of different mammals and casting doubt on some of those theories. Next, Let’s see what is known about why women live longer and what has been seen in other species.
On average, women live longer than men, with a difference of between six to eight years longer. 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, reaching the age of 122, born in 1875 and died in 1997.
Why women live longer has been a topic of debate in the scientific community There has been a lot of research that has tried to explain why this happens, 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, taking into account personality differences between the two sexes, women are less daring than men, which would make them take fewer risks. Others have raised the possibility that, since they are the ones who play more of a caring role than men, nature has taken it upon themselves to stretch their lives to ensure that they manage to raise their offspring until they are sufficiently autonomous.
A new study published this year 2020, carried out by Jean-François Lemaître’s group, has tried to find out why this is, comparing the differences in longevity between men and women and relating it to that of other mammal species. In general, they have observed that males tend to live less in at least 60% of the species studied but it does not seem that this is due to behavioral 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, to the detriment of that of the former.
Lemaître’s study investigated nearly 130 species, ranging from small, domestic sheep to large, imposing elephants. The greatest differences have been found in the Australian possum, lion, moose, killer whale, great kudu and sheep. For example, in the case of lions, females live twice as long as males.
Are personality differences to blame?
In both scientific and popular knowledge it is known that Men tend to make riskier decisions This lower respect for potentially dangerous situations has been related to the dimension of extraversion which, according to several studies, men have higher scores than women. This same dimension has been related 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 “Why do guys live less?”, pages that usually have an extensive archive of videos of men making really stupid and dangerous decisions.
Extrapolating it with the animal world, especially with mammals, One might think that males also tend to be more extraverted, but also violent, especially when it comes to sexual behavior. In many animal species, when two males have to compete for a female, they show off their strength: they fight with their antlers like elk do, scratch and mutilate each other like lions do, or kick each other like zebras do. There is physical fighting, there is damage.
However, Lemaître’s research seems to indicate that this is not actually the culprit. The study reveals that the intensity of sexual selection, whether through fighting or engaging in other risky behaviors, does not appear to be directly modulating the extent of differences in longevity between the sexes in the species seen. The results seem to indicate that it is rather due to complex interactions between the physiological characteristics of each individual dependent on sexual dimorphism.
In fact, there are species in which females live the least, 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 mammal species are usually smaller than males, in addition to having fewer distinctive features.
Instead, The larger males, when they grow, also develop very striking traits that require a high consumption of nutrients so that they 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 they would have to eat more than females to stay alive. If there is not enough food for your body, your body fails.
This has been observed in the case of the 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 the longevity of males and females On the other hand, in the wild, in areas where winter is especially harsh, males live much shorter than females.
Another of the explanations considered is that 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 at high levels, impair the immune response. Thus, males are more prone to diseases and pathogens than females.
Could chromosomes hold the answer?
Another study, carried out by Zoe A. Xirocostas, Susan E. Everingham and Angela T. Moles, compared the lifespans of about 229 species, including birds, insects and fish, in addition to mammals. This study found several species in which the opposite happens, that is, males live longer, and They related it to the type of sexual chromosome configuration they present
Humans and mammals, in general, 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, that is XX and ZZ, offers a longer life expectancy
