- Bats, lions, orcas. A team led by Jean-François Lemaître, CNRS researcher in evolutionary biology, has compiled the demographic data of 134 populations of wild mammals, from 110 species.
- As in humans, the observation is obvious: females live longer than men. Their longevity is on average 18.6% greater than that of males, when it is “only” 7.8% in humans.
- To biological and behavioral causes, Jean-François Lemaître also adds the environmental factor. The researcher answers 20 minutes.
Life expectancy at birth reached 79.8 years for men and 85.7 years for women in 2019 in mainland France, according to INSEE. What applies to France applies to the vast majority of countries: the life expectancy of women is greater than that of men.
"By 7.8%," says Jean-François Lemaître, CNRS researcher at the Biometrics and Evolutionary Biology Laboratory, in Lyon. "Nine out of ten supercentenarians (people over the age of 110) are also women".
Why ? Science is groping, Slate recalled in a February 2019 article. The causes would be partly biological - testosterone could alter human life from a medical point of view - and partly behavioral (on average, men drink more , smoke more, have more risky behavior…).
And what about other mammals? This is the question posed by fifteen researchers, including Jean-François Lemaître, in a study which appears this Monday in the scientific journal Pnas (Proceedings of the National Academy of Sciences) . Jean-François Lemaître answers our questions.
What is the genesis of this study already?
One of the themes we are working on, at the Biometrics and Evolutionary Biology Laboratory, is the ecology of aging. In other words, why we age and how to explain the differences in aging between species, and even between populations of the same species. In particular, we work a lot on deer, in which we follow individuals from two populations in the forest, from birth to death.
Among the factors that can play on aging, there is one that is particularly highlighted, taking the human being as an example: it is sex. We went to see if these differences between males and females are also found in nature. Similar studies have been conducted in the past. But either on datasets smaller than ours, or on captive populations. The interest of our study is to have collected data on 134 populations of 110 species of mammals, and thus to be able to draw a more general picture.
You come to the observation that, for 60% of the 134 populations studied, females live longer than males ...
In this study, for each of the populations studied, we took into account the individuals who survived until the age of first reproduction. Then, we calculated four measures of longevity, comparing each time male and female. Namely the maximum longevity (the maximum age that a species can reach even if a single individual reaches it), the average longevity (that is to say the life expectancy for an adult having survived until reproductive age), median longevity (the age at which half of individuals in the same population died), and finally the age at which 80% of individuals in the same population died. Of these four longevity measures, for 60% of the populations studied, the females presented superior results to the males. If we take these measures one by one, we often very much exceed this 60%.
Overall, we also observe that the longevity of females is on average 18.6% greater than that of males, while the difference is only 7.8% in humans. For some species, the differences are even more significant. This is the case of the lion, a species for which we have studied two populations. Three years after reaching the age of first reproduction, 50% of the males have already died. This was not the case until seven years later for the females. The differences are also very marked among the orcas.
Is it the reverse for some species: males live longer than females?
When we say that for 60% of the populations studied, females live longer than men, for the remaining 40%, in reality, the differences in longevity between the two sexes are just almost nonexistent. In rare cases, males live significantly longer than females in the species we studied. Except perhaps for myotis daubentonii and myotis lucifugus, two species of bat, where the difference was quite marked.
How to explain these differences in longevity in animals? Are the causes, there too, biological and behavioral?
It is an interest of the study in our eyes. By noting that overall, in mammals, females live longer than males, we tend to show that this difference is biologically very entrenched. And that the question of behavior [on average, men smoke more and drink more] would ultimately only play a marginal role.
However, aren't there also differences in behavior between males and females in many mammals?
Yes, there are differences in life strategies. In many species, males will have to allocate a lot more resources to sexual competition, control of a harem, defense of a territory or the conquest of a new one. This is indeed a factor that can modulate the differences in longevity between males and females. Clearly, by allocating a lot of resources to sexual competition, it is likely that males weaken their immune defenses and are therefore more exposed to the presence of pathogens in their local environment (viruses, parasites, etc.).
In our eyes, this local environment plays a lot in the differences in longevity, more than one could imagine. We can see this in our study concerning the species for which we were able to study two populations living in different environments. Between the two, the differences in longevity between the two sexes can be significant.
Planet
Survive rather than reproduce ... Leatherback turtles facing the dilemma of climate change?
Science
What is this secret of the bear that interests space conquest so much?
- Animals
- Science
- study
- Old age
- Mortality