There is a widespread belief that reproduction is always a sign of vitality. Yet, observing what happens in nature, the picture becomes more complicated. A large scientific study published in Nature shows that in many species the renunciation of reproduction is associated with a longer life. It is a result that emerges continuously in very different contexts and which concerns mammals, fish, reptiles and even humans.
This is not an abstract idea. The researchers compared fertile animals and animals subjected to sterilization or hormone control, noting that specimens that do not reproduce tend to live longer, in some cases up to 20% longer.
When reproduction stops, the body appears to age more slowly
Reproducing, from a biological point of view, is a huge investment. It means producing hormones, dealing with pregnancies, breastfeeding, competing with other individuals and defending resources. All this requires energy, which is taken away from other fundamental processes such as cellular repair and maintaining internal balance.
Analyzing data from more than one hundred species kept in zoos and aquariums, along with dozens of previous studies, researchers observed that neutered or spayed animals show a longer life expectancy than those that continue to reproduce. The effect is even more evident in harsh environments, where the body must make drastic choices about how to use its resources.
According to evolutionary biologist Shinichi Nakagawa, one of the authors of the study, this is the first time it has been demonstrated so clearly that intervening on reproduction can directly influence longevity, beyond factors such as diet.
Males and females: two different paths towards a longer life
However, the benefits do not follow the same path for everyone. In males, the difference is mainly made by hormones. The study makes it clear that blocking fertility is not enough: vasectomy, for example, does not significantly change lifespan. The case of castration is different, as it interrupts the production of sexual hormones.
In male animals lacking testosterone, aggressive behavior and the risk of dying in clashes or fights also decrease. Less competition, less exposure to unnecessary dangers. When the intervention occurs before sexual maturity, the effect on longevity is even more marked.
In females, however, the advantage derives above all from the absence of costs related to pregnancy and breastfeeding. Processes that put pressure on the immune system and increase vulnerability to infections. By blocking reproduction, the risk of death from infectious diseases is reduced and aging appears more gradual.
What does all this have to do with us
The authors of the study point out that these mechanisms are not far from human experience. We share the same physiological bases as the other species analyzed. Women, for example, live longer on average than men and menopause marks a natural end of the reproductive phase.
According to the researchers, stopping reproducing may have represented an evolutionary advantage, allowing greater survival in the later stages of life. Some historical data on castrated men, eunuchs, also point in the same direction and show a longer lifespan than their peers.
This does not mean, obviously, that giving up reproduction is a “recipe” for living longer. But the study reminds us of something fundamental: in nature every choice has a cost. Reproducing guarantees the future of the species, but does not always coincide with the maximum benefit for the individual. And this tension between survival and continuity seems to run through all life on Earth.
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