2023-10-26 20:00:07
Until now it was believed that only humanssome species of toothed and counted whales sea mammals they lived long years of active life after loss of reproductive capacity. For example, this same year, a study revealed that females of orcas They maintained their maternal involvement for life, even when the offspring had already become adults.
It is known that the orcas continue collaborating with your social systemthanks to a long life expectancy, for several decades after stopping having offspring.
About the female primatesHowever, it was thought that they maintained their reproductive capacity until stages very close to death. But now, a new study shows that a group of female chimpanzee (Pan troglodytes schweinfurthii) living in Uganda show signs of menopausethat is, they survive long after having lost their ability to have offspring.
the scientist Brian Wood and his team at the University of California (USA), the Max Planck Institute of Evolutionary Anthropology (Germany) and the Smithsonian Conservation Biology Institute (USA), among other institutions, contribute demographic and hormonal tests from menopause in chimpanzees wild who live in the jungle territory of Uganda. It should be remembered that chimpanzees, along with bonobos, are the closest relatives of hominids.
Female wild chimpanzees from the Ngogo community in Kibale National Park, Uganda, live 20% of their adulthood in a post-reproductive state
In this work, based on population and behavioral observations of a Ngogo community of chimpanzees—studied, for some time, in the Kibale National Park, Uganda— the team of scientists examined the mortality and fertility rates of 185 female chimpanzees during 21 years of observation (from 1995 to 2016). This information allowed them to perform calculations based on a metric called ‘Post-reproductive representation (PrR)‘, which is the average adult life ratio that happens in post-reproductive state.
Thus, the authors of the study that is published today in the journal Science show that Ngogo chimpanzees have a post-reproductive representation (PrR) of 0.2, meaning that, on average, females live the 20% of your adulthood in post-reproductive state.
Perhaps the lack of knowledge about menopause in animals simply came from the fact that humans had stayed away from these questions about our primate cousins. Today scientists are aware that understand the signs of menopause in animals savages can help us understand the evolution of this trait so normal in our own species.
Asked by SINC about the possibility that this same hormonal development occurs in other communities of chimpanzees (or other primates) in different geographies, Wood responds that “in other groups of chimpanzees, females have only rarely been observed to live beyond 50 years.” Furthermore, as she admits, “their patterns are unknown exchange hormonal around that age”, since “they have not been taken measures”.
A human-like hormone count
In human women, menopause usually occurs between the ages of 45 and 55, and is characterized by a natural decrease in reproductive hormones and a permanent cessation of ovarian function.
Marlene, a female who has lost her ovarian function, in the Ngogo community of Kibale National Park, Uganda. / Kevin Langergraber, Arizona State University
Explaining how menopause evolved represents a challenge because evolutionary benefits of this stage of life were not entirely convincing in the face of arguments that have usually been managed on the useful life of females. It is also not known with certainty why menopause would have evolved in humans and not in other long-lived primates.
While most mammals, including other chimpanzee populations observed, appeared to have a post-reproductive representation (PrR) close to zero – meaning a short survival after cessation of ovarian functionthis work discovers that, at least in that Ugandan chimpanzee community, fertility is not a vital requirement for females.
Fertility declined after age 30 and no births were observed to mothers over 50 years of age. According to the authors, similar hormonal variations are signs of human menopause
To evaluate non-pathological disruption of ovarian function, these experts analyzed 560 samples of urine of 66 chimpanzees females whose ages ranged between 14 and 67 years. These urine samples from females that differed in reproductive status and age demonstrate that transition to is post-reproductive state was marked by changes in hormones like gonadotrophins, estrogens and progestins.
Likewise, the Fertility declined after age 30 and, in the case of chimpanzees, no births were observed to mothers over 50 years old.
According to the authors, hormonal variations similar constitute signs of human menopause.
However, unlike humans, post-breeding chimpanzees in the Ngogo population they are not dedicated to create the your children’s childrennor can they be close to his daughters until they reach their own reproductive age, since the young adults emigrate to live outside their natal group. This would mean that the popular ‘hypothesis of grandmother’which has been used to reason about the adaptive evolution of long post-reproductive lives, is not applicable to the long existence of Ugandan chimpanzees.
One of the possible explanations This long period of non-fertile life of wild chimpanzees could be linked to a temporary response to some favorable ecological conditions in Ngogo, who contemplate low levels of predationalta food availability and successful competition between groups.
The second possibility, according to the results of the work, is that the substantial PrR is
and species-typical evolutionary trait in chimpanzeeswhich had not been observed elsewhere.
“The study by Wood and his team shows luz y raises questions about the evolution of menopause,” wrote the biologist Michael Cantwho did not participate in this research, in a review about work.
Garbo, a post-breeding female in the Ngogo community, Kibale National Park, Uganda. / Kevin Langergraber, Arizona State University
“It also highlights the relevance of the difficult field work long term—often carried out with reduced budgets and in constant closure risk— to transform the fundamental understanding of human biology and behavior,” Cant added.
For his part, Wood reminds Spanish-speaking readers that “the same community of chimpanzees that we have studied here also appears in the documentary series Chimp Empire (Chimpanzee Empire), available on one of the most popular viewing platforms in streaming.
Reference:
Wood, Brian et al. “Demographic and hormonal evidence for menopause in wild chimpanzees”. Science (2023)
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