Sixth species in the world: Wild Ugandan chimps go through menopause, 20-year-old study confirms!

The seemingly normal menopause phenomenon takes on a curious aspect when observed in wild animals. To date, scientists have confirmed menopausal symptoms in only six mammals, with most of them inhabiting aquatic environments.

In fairness, human beings exhibit rather unique behaviours compared to other species. We've developed societal structures and achieved feats that set us apart from the rest of the animal kingdom. Interestingly, we've even found a way to turn post-fertility into an advantage.

While menopause appears normal for us, it does raise questions about its evolutionary implications, since it also hinders passing on of maternal genes to offspring. This is where the "grandmother hypothesis" comes into play, suggesting that as females age, it becomes more energy-efficient to support their grandchildren's survival rather than having more children of their own, which also serves their genetic interests.

The true reason behind menopause remains a topic of debate and doesn't seem to be a widely adopted evolutionary strategy. Most species can reproduce until their end of life. However, wild chimpanzees from Uganda now join the shortlist of menopausal animals, which includes killer whales, pilot whales, belugas, narwhals, and humans.

A comprehensive two-decade study on the Ngogo community of wild chimpanzees in Uganda's Kibale National Park has revealed that these close relatives of humans begin to exhibit menopause-like symptoms at around age 30. Following two decades of declining fertility, there have been no observed births after the age of 50, indicating a similar loss of reproductive ability compared to humans.

However, reaching menopause doesn't signify the end of their lives. Similar to humans, many female chimpanzees live beyond the age of 50, and they don't appear particularly interested in caring for their grandchildren, which challenges the grandmother hypothesis.

The evolutionary purpose behind this mechanism remains a subject of speculation. One possibility is that it might be a temporary response, given that post-reproductive lifespans have primarily been observed in captive chimpanzees rather than their wild counterparts, potentially indicating a response to favourable ecological conditions.

Alternatively, menopause could be a natural evolutionary trait for these chimpanzees that we haven't observed extensively due to human activities and diseases that have negatively impacted their populations, causing them to die at a younger age.

In the words of study author Brian M. Wood, "We now know that menopause and post-fertile survival arise across a broader range of species and socio-ecological conditions than formerly appreciated, providing a solid basis for considering the roles that improved diets and lowered risks of predation would have played in human life history evolution."