According to a study, female chimpanzees in the wild have a long lifespan after they have gone through menopause.
Researchers have discovered that female chimpanzees in their natural habitat experience menopause and can live for a substantial amount of time afterwards. This indicates that menopause may be more common among chimpanzees than previously believed.
The reason behind why certain female mammals have an extended lifespan after they are no longer able to reproduce has been a perplexing question for specialists. This phenomenon was believed to only occur in humans and five types of whales, and its significance has been a topic of much discussion.
Researchers have recently discovered the initial proof of this occurrence within a wild non-human primate.
The researchers have reported that both humans and wild chimpanzees experience the end of reproductive years around age 50. They also found that it is not uncommon for chimpanzees, like humans, to have longer lifespans.
Researchers published a study in the journal Science that details their observations of 185 female wild chimpanzees in the Ngogo community of Kibale national park, Uganda, from 1995 to 2016.
The researchers discovered that the likelihood of chimpanzees giving birth decreased after they reached the age of 30, and no births were observed in chimpanzees over 50 years old.
However, 16 females lived beyond this age. Indeed the analysis suggests females lived about one-fifth of their adult life in a post-reproductive state.
The researchers also examined urine samples from 66 female chimpanzees and found that they experience hormonal changes similar to those observed in menopausal human females as they age.
Previous research has not discovered significant amounts of female chimpanzees in a post-reproductive phase in the wild. The researchers suggest that this could be due to the favorable conditions at Ngogo, which may enable more females to live longer.
Comparable reasoning has been presented to clarify the reasoning behind why several species, such as chimpanzees, experience menopause while in captivity.
The team suggests that there is a potential alternative explanation: in the past, chimpanzees may have experienced a long period of life after they were no longer able to reproduce. However, human interference in areas besides Ngogo, leading to sickness and loss of habitat, has negatively affected the survival of wild chimpanzee communities, particularly older females.
There are still uncertainties. Dr. Kevin Langergraber, a co-author of the study at Arizona State University, stated that it is unclear how selection could promote the continuation of lifespan beyond the age of reproductive ability.
Langergraber proposed the concept of the “grandmother hypothesis,” which suggests that this phenomenon exists in order to allow older females to assist their extended family. However, this theory seems improbable in chimpanzees due to their social dynamics. Langergraber did acknowledge that it could serve as a way to reduce conflict with younger females over potential mates.
Dr. Megan Arnot, an anthropologist specializing in evolution at University College London, stated that the research supports the notion that human menopause may be a result of longer lifespans in modern times compared to our evolutionary history, and that the female reproductive system has not yet adapted to this change.
However, she noted that this theory does not account for why women experience menopause at midlife or why humans have a longer lifespan beyond it.
She stated that there is still much to learn about menopause and the period after reproduction in humans.