in breakthrough discovery, researchers found that female chimpanzees at Ngogo Reserve spend about 20 percent of their adult lives in a menopausal state, surviving well past the end of their reproductive potential. The discovery complicates the mystery of why some species, including humans, experience menopause from both a practical and an evolutionary perspective.
“No one would have imagined that [menopause] This was also observed in chimpanzees,” said study author Brian Wood. “Now we understand what the ecological and social conditions are necessary for it to emerge.”
Although captive chimpanzees have previously shown signs of menopause, researchers have struggled to document similar behavior in wild populations. The authors said part of the reason may be that most female chimpanzees don’t live long enough to reach the biological stage where they stop reproducing.
“Due to recent negative impacts from humans, most chimpanzee populations do not reach age 50,” said study author Kevin Langergraber, an anthropologist at Arizona State University. For example, he said, humans could transmit even simple diseases like the common cold and wipe out chimpanzee populations.
Enter Ngogo, a chimpanzee paradise.
Ngogo is relatively uninhabited and is one of two research sites managed by the Ugandan government within Kibale National Park. Fig trees provide chimpanzees with an abundant and steady supply of fruit. They also have few natural enemies such as leopards. Here, these chimpanzees can live long lives. The adventures of the Ngogo primates, the world’s largest group of chimpanzees, were chronicled in the Netflix series Chimpanzee Empire, released this year.
Garbo, who appears in the Netflix series, is the oldest living chimpanzee in the area, although two females in the past have reached the age of 69. Ma Rainey, who is about 63 years old, lives in the area with her son, Wes. Another woman, Ms. Sutherland, 61, is also nearby.
Langergraeber said these older women tend to be less sociable and spend more time alone, likely because they are physically weakened by this point. You lose muscle mass, become thin, gray, bald, wrinkled, and have more spots. Teeth also wear down.
““Ngogo is different from other chimpanzee groups in that we have many females who live past the age of 50,” said Langergraeber, co-director of the Ngogo Chimpanzee Project. “For a long time, we noticed that there were a lot of old females running around in the forest that hadn’t bred for a long time.”
Researchers collected demographic and hormonal data on female members of the community over 20 years of observations. They looked at mortality and birth rates in 185 chimpanzees and found that, on average, females spend about one-fifth of their lives in a post-reproductive state.
The researchers also tested urine samples from 66 females at various reproductive stages, collected from leaves or caught on plastic sheets. Researchers found that, like human women who go through menopause, older female chimpanzees experience changes in hormones such as gonadotropins, estrogens, and progestins. The timing of these hormonal changes is similar to that in humans; they gradually decrease after the age of 30 and stop around the age of 50.
“The fertility patterns of Ngogo and humans are actually similar,” Langergraeber said. “This is the same physiological mechanism underlying reproductive arrest in chimpanzees as in humans.”
But explaining why menopause occurs in chimpanzees and humans is a much more difficult problem. Menopause has long been a mystery to scientists. If reproduction is an animal’s genetic priority, why do some animals live far beyond their capabilities? The answer appears to be different for chimpanzees and humans.
In humans, one prevailing theory is that older women stop bearing children to help raise their offspring, known as the “grandmother hypothesis.” However, this is not the case with chimpanzees. Because daughters are separated from their mothers and basically never see them again. A mother can help raise her son, but previous research showed that this is not the case.
Still, this striking similarity may shed light on how human menopause evolved. Given that chimpanzees are our closest relatives, these results suggest that postmenopausal survival may be a trait inherited from a common ancestor millions of years ago. Masu. But perhaps this trait subsequently emerged only under specific circumstances that allowed for long lifespans.
“The ability to live longer after reproduction may have been widespread in our great ape ancestors,” said behavioral ecologist Phyllis Lee, who was not involved in the study. “This potential for prolongation may underlie a universal feature of menopause that is actually only found in humans.”
Mr Lee, a researcher at the University of Stirling, praised the study, saying it was “very well done” and required a huge investment in observation and hormone collection.
Questions remain about how widespread menopause is throughout the chimpanzee population. For example, the research team wants to know whether Ngogo’s survival rate was an anomaly and caused menopause.Or is the relatively low survival rate in other wild chimpanzee habitats an anomaly compared to the past evolutionary history of chimpanzees??
“We told very human, specific stories. [menopause]Because that’s the species we know best,” Wood said. “I think this study will lead to an expanded understanding and broader understanding of the multiple different factors that may have influenced its evolution in our species.”
