The orca is one of only a handful of mammals known to go through menopause. The reason has remained murky, but now, new research suggests why: Grandmothers boost the survival of their grandcalves.

Scientists who analyzed decades of orca populations in the Pacific Northwest found that young orcas with grandmothers were more likely to stay alive than those without. What’s more, a calf’s risk of death rose dramatically for two years following the death of its grandmother. Because orca (also known as killer whale) societies are matriarchal, it’s likely that these older females carry with them crucial knowledge about food resources that can mean life or death for their kin.

“[A killer whale grandmother’s] greater knowledge and their leadership,