When an orca grandmother dies, her grandcalves start dying too. Researchers followed killer whale families off the Pacific coast for forty years and found a calf that lost its grandmother was 4.5 times more likely to die in the two years after.
The reason is knowledge. She knew where the salmon were. Old females lead the pod, and they lead it most in the lean years, when fish are scarce and memory is worth more than strength.
Elephants make the same case, and this one can be dated. In the 1993 drought at Tarangire, two herds walked out of the park to find water and survived. One stayed, and lost most of its calves.
The two that left were led by matriarchs old enough to have lived through the last great drought, in 1958. The one that stayed was led by a female born after it.
A grandmother carries the map her family navigates by, and when she goes it goes with her.