Of all the species on the planet, only three experience menopause—killer whales, humans and short-filled pilot whales. For more than 40 years, researchers have studied the latter and have uncovered the reason that older females lose the ability to have children and continue live for decades after.
Through a long-term study of the lives and deaths of orcas in the same pod in the Pacific Northwest, scientists from the University of Exeter found a clue as to why female killer whales stopped reproducing later in life. Although female killer whales stop conceiving calves in their 30s and 40s, they can go on to live to 90 years old. When the older whales reproduced alongside their daughters, their calves were nearly twice as likely to die during their first 15 years of life. For this reason, older female whales take on a different nurturing role in the pod by sharing food with the other whales and helping to provide for her children and grandchildren, thereby ensuring the survival of the entire family.
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“Our previous work shows how old females help, but not why they stop reproducing,” said behavioral ecologist and University of Exeter professor Darren Croft. “Females of many species act as leaders in late life but continue to reproduce, but this new research shows that old females go through menopause because they lose out in reproductive competition with their own daughters.”
What is clear to scientist is that menopause is no accident; it’s an evolutionary trait made necessary by conflict and cooperation within the family groups. Professor and study co-author Mike Cant, said, “It means that we’ve captured a key piece of the puzzle of post-reproductive life. We can now explain not just why older females live so long after reproduction, but why they stop breeding in the first place.”