The longevity disparity between men and women may have its origins in ancient biological mechanisms, going beyond simple behavioral factors.
An unprecedented comparative analysis, examining survival patterns in mammals and birds, sheds light on the fundamental causes of this persistent gap. This work reveals surprising evolutionary constants that suggest our prolonged existence bears the imprint of millions of years of biological adaptation, where reproductive strategies and chromosomal configurations play a determining role.
The influence of chromosomes on longevity
The sex determination system significantly influences lifespan, with female mammals benefiting from two X chromosomes that offer protection against certain deleterious genetic mutations. This advantageous configuration contrasts with that of males, endowed with one X chromosome and a more vulnerable Y chromosome, which could largely explain this difference in longevity.
The study published in
Science Advances reveals a complete reversal of this trend in birds, where males have a ZZ chromosomal configuration considered biologically advantageous. Females, on the other hand, have ZW chromosomes that are potentially less favorable, a reversal that perfectly matches the observation of superior male longevity in this group.
Some species, however, contradict this general rule, such as female raptors who often live longer despite their unfavorable heterogametic status. These notable exceptions indicate that research must integrate other explanatory parameters beyond chromosomes alone, which therefore represent an important piece without constituting the sole explanation for this phenomenon.
Reproductive strategies and parental investment
Reproductive competition exerts a determining influence on male mortality, pushing male mammals to develop physical attributes that are costly in terms of energy. The active search for partners and fights between competitors simultaneously increase their vital risks, thus creating a cumulative effect of evolutionary pressures that significantly reduces their overall life expectancy.
Monogamous species show much less marked longevity gaps, because intersexual competition is considerably attenuated in favor of enhanced collaboration. Monogamous birds perfectly illustrate this attenuation of differences.
Parental investment represents another determining factor, with female mammals generally providing the majority of care for the offspring. Their prolonged survival guarantees the reproductive success of their descendants, which explains why natural selection has favored their long-term endurance in many species, particularly among primates.
To go further: How do sex chromosomes affect aging?
Sex chromosomes carry genes essential for cellular function, with the X chromosome containing many vital genes linked to the immune system. Its duplication in females offers protection against deleterious mutations, this genetic redundancy constituting a definite advantage that manifests throughout life.
The Y chromosome is reduced in size and has few functional genes, so male mammals cannot compensate for genetic defects affecting their single X chromosome. Their increased vulnerability to diseases manifests progressively during aging, this genetic disadvantage durably influencing their health trajectory.
Birds exhibit a reversed but equivalent chromosomal configuration in its consequences, with their females possessing a genetically impoverished W chromosome, similar to the Y in mammals. Males, on the other hand, benefit from two complete and functional Z chromosomes, this inversion explaining their survival advantage in most species studied.
What role does sexual selection play in mortality?
Sexual selection pushes males to develop extreme physical traits that consume significant energy resources normally dedicated to bodily maintenance. Their immune systems are consequently durably weakened, which compromises their resistance to pathogens and accelerates their physiological decline.
Competitive behaviors generate immediate risks to physical integrity, with fights between males causing sometimes fatal injuries or lasting sequelae. The active search for partners simultaneously exposes them to multiple environmental dangers, these cumulative factors mechanically reducing male life expectancy.
Polygamous species show the most spectacular longevity gaps, because competition reaches particularly intense and constant levels there. Males devote a considerable proportion of their vital energy to reproductive rivalry, their long-term survival inevitably suffering as a result in favor of immediate reproductive success.
Article author: Cédric DEPOND