It is well known that women live longer than men. There are more widows than widowers and, in addition, there are many more women who become super-centenarians than men.
Biology has attempted to uncover the why of all this, by proposing various theories to explain, in particular, the differences in longevity between the sexes in the human species and, more generally, by extrapolating to other species.
However, a very recent study addressed this question, comparing the life expectancies of different mammals and questioning some of these theories. Then, let’s see what we know about the reasons 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 years longer. A fairly revealing fact about this is that of super-centenarians, that is, people living over 110 years old, 9 out of 10 are women. In fact, the person who 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 the subject of debate in the scientific community. Much research has attempted to explain why this happens, linking its medical and economic implications, and trying to see what differences in lifestyle might account for this increased longevity in women.
It has been argued that given the personality differences between the two sexes, women are less daring than men, which would make them take less risk. Others raised the possibility that, being those who play a more caring role than men, nature has taken it upon itself to stretch their lives to ensure that they can raise their children until they are sufficiently autonomous.
A new study published this year 2020, led by the group of Jean-François Lemaître, tried to understand why this, by comparing the differences in longevity between men and women and by relating them to those of other species of mammals. In general, they observed that males generally live less in 60% of the species studiedBut that doesn’t seem to be due to behavioral aspects.
Male mammals live less
As we have seen, it’s not just 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 the former.
Lemaître’s study studied around 130 species, ranging from small domestic sheep to large towering elephants. The biggest differences were found in the Australian opossum, lion, elk, killer whale, greater kudu, and sheep. For example, in the case of the lion, females live twice as long as males.
Is it about personality differences?
In scientific and popular knowledge, we know that men tend to make riskier decisions. This less respect for potentially dangerous situations has been linked to the dimension of extraversion which, according to various 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, and it’s not hard to find websites titled “why do guys live shorter?” or “Why do uncles live less?” pages that often contain extensive newspaper archives with videos of men making really stupid and dangerous decisions.
Extrapolate with the animal world, especially with mammals, you would think that men also tend to be more outgoing, but also violent, Especially with regard to sexual behavior. In many animal species, when two males have to compete for a female, they show strength: they fight with their horns like moose do, they scratch and mutilate themselves like lions, or they get kicked like they do. do. There are physical fights, there is damage.
However, Lemaître’s investigation seems to indicate that it is not the culprit in reality. The study reveals that the intensity of sexual selection, whether through fighting or engaging in other risky behaviors, does not appear to directly modulate the magnitude of the differences in longevity between the sexes in the species observed. The results seem to indicate that this is rather due to complex interactions between the physiological characteristics of each individual. depends on sexual dimorphism.
In fact, there are species in which females live the least, and one of the explanations for this is that they have characteristics that are not to their advantage due to the environment in which they must have lived. In the case of most species of mammals, it is the males that have physical characteristics that are not beneficial to them.
Longevity in women
Another of the explanations offered concerns energy expenditure, which is different between men and women. Females of many species of mammals tend to be smaller than males, in addition to having fewer distinguishing features.
However, older males also develop very prominent traits that require a high intake of nutrients so that they develop fully, like horns, a hairier coat, more muscle mass …
It 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, the body fails.
This has been observed with the case of the wild 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 the longevity of males and females.. In contrast, in the wild, in regions where winter is particularly severe, males live much less than females.
Another of the explanations studied is that males produce more androgens than females. In fact, these hormones are called male hormones. Androgens modulate the efficiency of the immune system and, when presented at high levels, alter the immune response. Thus, men are more prone to diseases and pathogens than women.
Could chromosomes have the answer?
Another study, led by Zoe A. Chirocostas, Susan E. Everingham, and Angela T. Moles, compared the life expectancies of about 229 species, including birds, insects, and fish, in addition to mammals. This study revealed several species in which this occurs the other way around, i.e. males are the ones who live the longest, and they linked it to the type of sexual chromosome setup they have.
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. Women are ZW, while men are ZZ. This study found evidence to have a pair of the same type of sex chromosomes, that is XX and ZZ, offers a longer life expectancy.
- Lemaître, JF et al. (2020) Sex Differences in Adult Life and the Aging Mortality Rate in Wild Mammals. PNAS. doi.org/10.1073/pnas.1911999117.
- Xirocostas, ZA, Everingham, SE and Moles, AT (2020). Sex with a reduced sex chromosome dies earlier: a comparison between the tree of life. Letters of Biology, 16 (3): 20190867. http://dx.doi.org/10.1098/rsbl.2019.0867.