The study indicates that mountain gorillas also go through menopause

Mountain gorillas, a species that goes by the scientific name Gorilla beringei beringei, have just become part of a rare group of species that undergo menopause, a condition until recently thought to be exclusive to humans.

The discovery was made by researchers at the Max Planck Institute for Evolutionary Anthropology in Germany and recently published in the scientific journal PNAS.

The study was conducted by scientists Nikolaos Smit and Martha Robbins, who analyzed decades of observations on the population of these primates in Bwindi Impenetrable National Park, Uganda, in east-central Africa.

In this isolated environment, the researchers followed 25 adult female gorillas and found that seven of them lived at least a decade after their reproductive period ended.

Two reached almost 50 years of age, an age rarely reached by gorillas in the natural environment.

According to an article in the newspaper Folha de S.Paulo, to define the so-called “post-reproductive lifespan”, scientists took into consideration the average interval between the births of puppies, which varies from four to six years.

When a female spent double that time without having new offspring, and also without recording activity with partners, she was considered to be in the post-reproductive stage.

Most of these females were over 35 years old, the upper limit already observed for births in the wild, and had not had sexual intercourse for more than seven and a half years. According to estimates, they spend about 10% of their adult lives in this phase – starting from the age of ten -, a percentage similar to that of human menopause.

Scientists still do not say with certainty that the phenomenon is identical to what happens in women, since the absence of new children could be explained by spontaneous abortions or gestational complications at an advanced age.

Even so, hormonal analyzes of older females revealed changes similar to those recorded in humans during menopause, suggesting that the phenomenon may indeed be present among mountain gorillas.

If the results are confirmed, Bwindi gorillas will become part of a very small group of mammals with this characteristic.

So far the phenomenon has only been documented in some species of cetaceans with teeth – such as orcas, belugas and narwhals – and in the chimpanzees of a population of Ngogo, also in Uganda.

The presence of menopause in animals raises a fascinating question: why would evolution preserve a trait that, at first glance, appears to reduce the chances of reproduction?

From the point of view of natural selection, formulated by Charles Darwin in the 19th century, failing to reproduce during part of one’s adult life would seem disadvantageous.

Fewer offspring means fewer opportunities to pass on genes. However, there is another way to ensure evolutionary success: instead of having many offspring, a female can invest more energy and time in caring for some of them, increasing the likelihood that they will survive and reproduce.

It is from this logic that the so-called “grandmother hypothesis” arises. According to her, after failing to produce new offspring, a female begins to focus her efforts on caring for her grandchildren, which, indirectly, keeps her genetic legacy alive. This theory helps explain menopause in species with complex family structures, such as humans and orcas.

In the case of mountain gorillas, however, the explanation could be different. Because females often change groups throughout their lives, they often do not stay close to their offspring to care for grandchildren, which weakens the grandmother hypothesis.

The researchers therefore suggest an alternative: the “mother hypothesis”. According to this idea, the post-reproductive period would serve to allow females to complete the rearing of older offspring, offering support and protection during maturation, as well as contributing to the social stability of groups.

Further long-term studies will still be needed to confirm this hypothesis, but Smit and Robbins’ work opens a new window into understanding how evolution has shaped the life cycles of great apes – and, by extension, the human species itself.

Among Uganda’s dense forests, mountain gorillas may reveal a surprising link between us and our closest relatives.