A team of scientists discovered that narwhals and beluga whales experience menopause, which brings the total number of species known to experience the process to five. Humans aside, the species known to experience menopause all belong to the toothed whale parvorder.
“For menopause to make sense in evolutionary terms, a species needs both a reason to stop reproducing and a reason to live on afterwards,” said Sam Ellis of the University of Exeter, first author of the study. “In killer whales, the reason to stop comes because both male and female offspring stay with their mothers for life—so as a female ages, her group contains more and more of her children and grandchildren.”
“This increasing relatedness means that, if she keeps having young, they compete with her own direct descendants for resources such as food,” he added.
“The reason to continue living is that older females are of great benefit to their offspring and grand-offspring. For example, their knowledge of where to find food helps groups survive.”
More than four decades of intense study has documented the existence of menopause in killer whales.
“It’s hard to study human behaviour in the modern world because it’s so far removed from the conditions our ancestors lived in,” said Darren Croft, senior author of the study. “Looking at other species like these toothed whales can help us establish how this unusual reproductive strategy has evolved.”
Despite the fact that many individuals in various species fail to reproduce later in life, the team looked for evidence that suggested an “evolved strategy” where females had a post-reproductive lifespan.
The findings were published in Scientific Reports.