That women live longer than men is not new, but a recent study published on October 1st on Science Advances he found that this trend is common to almost all mammalswhile in birds is exactly the opposite: it is the males who have the privilege of the longevity. The explanation lies in an intricate mix of both biological and genetic factors, such as heterogamy (i.e. the presence of two different chromosomes, xy in the males mammals and ZW in the females of birds), and social and environmental, such as the competition for mating and the care of the offspring. Researchers from all over the world participated in this interesting research led by Dr. Joanna Staerk of the Department of evolution and behavior of the primates of the Max Planck Institute for Evolutionary Anthropology. Using the Species360 zoological information management system (ZIMS, a software that serves zoo and aquariums all over the world) the researchers were able to analyze 1176 species, between mammals (528) and birds (648).
The results confirmed previous theories and hypotheses: In 72% of the species of mammals analyzed, the females live longerabout 12% more than male specimens. On the contrary, in 68% of bird species It is males who have greater life expectancy, but they live only 5% more than female specimens. And also in “protected” conditions such as zoo, in which the competition for mating and other environmental factors are eliminated, the result, albeit attenuated, does not change.
In nature or zoo, the result is the same
Analyzing 110 species in naturethe researchers confirmed that these schemes are solid and do not depend on living conditions. In zoo, animals have no predators, they have all the food necessary, veterinary care and must not submit to the “largest law” for reproduction. But the differences between males and females remain anyway, albeit attenuated. Obviouslyin nature, the gap between male and female longevity is clearly higherbut the fact that this difference also note in the controlled zoo environments, is a demonstration of how evolution plays a fundamental role even when environmental stimuli are reduced to a minimum.
The differences between chromosomes between males and females in mammals and birds
One of the most accredited theories for this difference in longevity, calls into question i sex chromosomes, Assuming that sex with two different chromosomes is genetically weaker. In the specific case, the males of mammals have XY chromosomes, in birds instead it is females to have different chromosomes, ZW.
In both cases, therefore it seems that the Sex with equal chromosomes is longest (XX, females in mammals and male zz in birds): having two copies of the same chromosome is more advantageous because, if one of the two is present a mutation, there is always the other to balance. It is a bit like having two copies of the same book: if in one there is a ruined page, you have the other who is intact instead. However, this theory alone It is not enough to explain the observed exceptions in nature.
Fatal costs of coupling for males
And if genetics and chromosomes are not enough to explain this difference in life expectancy, we must look elsewhere: to coupling and reproduction strategies. In mammals polygamicThat is, that they mate with more partners, the struggle to guarantee one is ruthless: the competition between males leads them, in fact, more often to “pay” a high price, in terms of survival. A further observation in support of this thesis is that in species of mammals where males are much larger than females (in technical jargon, when there is a marked sexual dwelling), these tend to live less. In practice, invest in mating, with territorial struggles, fights For the domain or partners, it involves a huge energy expenditure and a greater exposure to dangers, translating into one shorter life.
To further confirm this, the researchers found that in the monogamous coupleswho pass their life together like two lovebirds, the difference of life between males and females is drastically reduced, almost up to cancel. A real “and they lived happy and happy”.
Take care of the offspring lengthens life
In terms of energy consumption, also reproduction and subsequent care of the offspring, often the prerogative of the females of the species, require high energy costs, suggesting an early deterioration. Instead, however strange it may seem, this study showed exactly the opposite: take care of the offspring increases the possibilities of survival.
In females of primates, for example, the puppy remains with his mother up to almost ten years: researchers speculate that the evolutionary pressure does survive longer the sex that deals with puppies, until they are independent. It is no coincidence that even in birds, especially monogamous species in which The males participate more in the care of the offspringsurvive longer.
Made the rule, found the exception
Obviously, we are not talking about dogmas written in the stone. Also in this case there are exceptions. For example, despite the energies that birds consume for extravagant plumages And courtship rituals developed, however they live more than females, further confirmation that is the mix of the various factors that determine the greatest longevity of one or the other sex.
In mammals like lemuri, where females are dominant and there is no monogamy, there are no differences in longevity between males and females. On the contrary, in the birds of prey, the females are larger, but However, they live more than malesoverturning the scheme identified in birds.
