Scientists have made a groundbreaking new discovery about killer whales that could shed light on why women go through menopause. Humans are one of just three known species to experience menopause, and one of the others, killer whales, could hold the key as to why.

A new study published in the journal Current Biology has found that female killer whales get more generous with sharing food as they get older, ensuring that older mothers don’t starve calves as a result of their increasing generosity, according to a University of Exeter statement.

Because calves never leave their mother, as the female killer whale gets older, she has more offspring around and becomes increasingly closely related to the rest of the group. She’s also more interested in investing resources like food in the group, whereas a young mother would be more focused on her own offspring. But calves from older killer whales would be penalized, as would the mother, as it would take an intense amount of energy.

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.”