Sex comes with a biological cost in virtually all vertebrates (even us). Apart from dietary restriction, interruption of reproduction is one of the few documented examples of an external intervention capable of prolonging life.
A new large-scale study suggests that interrupt reproductive capacityvia surgical sterilization or hormonal contraception, is associated with a consistent increase in longevity in several vertebrate species, with estimated average gains between 10% e 20% in life expectancy.
The authors argue that, in addition to dietary restriction, this is one of the few documented examples of an external intervention capable of prolonging life in vertebrates, pointing to a “biological cost” inherent to reproduction.
The work, conducted by an international team and published in , included two complementary approaches. On the one hand, researchers analyzed records of 117 species kept in zoos and aquariums in different countries. On the other hand, they carried out a meta-analysis of 71 previous studies, gathering evidence from groups such as rodents, primates, fish and reptiles.
In both sets of data, animals that were sterilized or given hormonal reproductive control lived, on average, longer than individuals that maintained reproductive capacity and went on to reproduce.
The central hypothesis is that reproduction “drains” resources and energy from the organismincreasing vulnerability to diseases and accelerating processes associated with aging, according to the authors, cited in a statement from the University of Otago cited by . The environment can mitigate or exacerbate this cost that comes with reproduction — including the human environment, where factors such as health care, nutrition, and social support networks can act as buffers.
Although the general pattern is common to both sexes, the study describes distinct mechanisms for males and females. In the case of males, the authors conclude that the improvement in survival is strongly linked to the reduction of sexual hormones, in particular testosterone. Mike Garrattlead author of the study, states that the effect was observed mainly after castration, and not after vasectomy: vasectomy prevents the passage of sperm, but does not significantly reduce hormonal production.
In species where vasectomy is more common than castration, such as the lion, researchers have not detected clear differences in longevity between surgically sterilized animals and non-interventional individuals.
The data also suggests that the timing of the intervention makes a difference: when castration occurs after puberty, life expectancy increases, on average, by around 9%. When performed before sexual maturity, the average gain rises to approximately 14%, which may indicate that sex hormones interact with biological pathways associated with aging, especially during early stages of development.
The effects also vary according to the causes of mortality. In males, the Reducing testosterone appears to reduce risky behaviors and the likelihood of death associated with aggression and confrontation. The study estimates a reduction of about 12.8% in mortality linked to behavioral interactions in older males when reproduction is inhibited. In females, the benefit arises mainly through the reduction in deaths from infectionspossibly because pregnancy and lactation can temporarily suppress the immune system. The team reports a drop of around 13,4% in the risk of death compared to control groups.
In rodents, some studies included in the meta-analysis also point to improvements in “healthspan” — the period of life with good functionality — such as gains in cognition and balance, particularly in males. In females, removal of the ovaries appears to reduce tumors of the reproductive system, although some tests report negative effects on activity and cognitive performance.
The authors argue that these tendencies cross the animal kingdom and that the “hormonal drive” to reproduce limits adult survival “regardless of the environment” in which the species lives, with potentially stronger effects on naturewhere energy is scarcer and competition is more intense.
As for the implications for humans, the researchers emphasize that we share physiological systems similar to those of many of the species analyzed, but avoid direct extrapolations. Still, they suggest that phenomena such as menopause may have been evolutionarily favored if reproductive cessation increases survival into old age. The team relates this possibility to the so-called “grandmother effect”, in which the greater longevity of older women may benefit offspring by increasing support and care, rather than prolonging reproduction.
