A big new discovery by researchers at the University of Exeter and published in the journal Current Biology claims to have finally answered the question of why humans — and just two other species in the world — get menopause, a strange quirk of biology that hasn’t seemed to make sense until now.

Scientists made the finding by studying the killer whale, which is one of the other species that gets it. The study found that female killer whales tended to get more generous with sharing food with other whales as they got older, which would be a problem for their calves if they continued having them at an advanced age, according to a statement from the university.

Calves never leave their mother, so as the female killer whale gets older, it would have to continue to feed more and more offspring, all the while sharing more and more with the group, and impossible task eventually if she continued having calves. It’s not quite an apples to apples comparison with humans, but it could help explain how something like menopause ends up in the evolutionary process for humans, and provides a new avenue of research for scientists trying to understand the phenomenon.

Professor Darren Croft explains in the statement that “older females are more closely related to the family group than younger females. This imbalance in local relatedness between mothers and their own female offspring means that older females do best to invest more heavily in the wider family group whereas younger females should invest more in competition.”

“Our previous work shows how old females help but not why they stop reproducing,” Croft said. “Females of many species act as leaders in late life but continue to reproduce, but this new research shows that old females go through the menopause because they lose out in reproductive competition with their own daughters.”