"When we look at the healthiest individuals, it looks like chimpanzees may actually be reproducing better than humans in their forties," researcher Melissa Emery Thompson, of Harvard University, said in a prepared statement. "The oldest chimpanzee known to give birth in the wild is estimated to have been 55. She began reproductive cycling again shortly before her death at the age of 63."
Thompson's team analyzed fertility rate data on female chimpanzees in the wild. They found that they, like humans, have declining birth rates after the age of 40. This suggests that the "biological clock" in humans has been relatively preserved over the course of evolution, the study authors said.
However, unlike humans, female chimpanzee fertility tends to decline along with their survival odds. Healthy females maintain high birth rates late into life.
"The adaptive significance of human menopause, or post-reproductive life span, is still debated. This study provides greater evolutionary context to this debate," Thompson and her colleagues wrote.
These findings in chimpanzees, along with recent findings in wild gorillas and orangutans, indicate that "menopause is not part of the life cycle of living apes but has been uniquely derived in the human lineage."
The study is published in the Dec. 13 issue of the journal Current Biology.
More information
The U.S. National Institute on Aging has more about menopause.
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