āLife after menopause is exceptionally rare in animals. It can evolve only in creatures where grannies help younger family members survive. Only human, killer whale, and short-finned pilot whale females routinely live for substantial periods after they stop breeding. Like humans, killer and pilot whales have roughly twenty-five to thirty childbearing years, then can live another thirty or so. And as Kenās just explained, some live a lot longer. Up to a quarter of the females in a group are postreproductive. These whales are not waiting to die; they are helping their children survive. As human children often benefit from their grandmothersā attention, killer whale grandmothers boost their grandkidsā survival. A rather bizarre twist of killer whale society is that killer whale mothers remain crucial to the survival of their adult children. When older killer whale females die, their adult children start dying at high rates, especially males. Male killer whales who are under thirty years old when their mothers die suffer a tripling of the annual mortality rate compared to males in their age group whose mothers are still alive. Male killer whales who are more than thirty years old when their mothers die face death rates more than eight times as high as males in their age group whose mothers are still living. Daughters under thirty show no mortality increase after their mothersā death. But daughters older than thirty when their mothers die have more than two and a half times the death rate of same-age females whose mothers are alive. Malesā handicaps of the extra drag of their huge dorsal and pectoral fins and the extra food required for their immense size (at around 20,000 pounds, males can be one-third more massive than females) seem to make them reliant on their working mothers for food. Females donāt have the malesā impediments, but while raising young, females may rely on food shared by their no-longer-breeding mothers. Adult females share essentially all the fish they catch, and more than half goes to their children. Adult males share their catch only about 15 percent of the timeāusually with their mothers. While no one fully understands their strange death pattern following the loss of a mother, extreme parental care is likely at the root. Toothed whales are the worldās champion nursers. Short-finned pilot whales continue to produce milk for up to fifteen years after the birth of their last calf, likely nursing other femalesā young. In bottlenose and Atlantic spotted dolphins (further study might reveal others), some females never give birth. Denise Herzing dubbed them ācareer females,ā because their role in society does not include motherhood. They might be infertile. They might be gay. But their contribution is crucial: they do a lot of babysitting. When Herzing entered the ocean with a visiting nine-year-old girl, āWhite Patches, the eternal babysitter herself, had never seen me babysitting a young human before. Her excitement vocalizations were audible and electric and she continued to swim around us, eyeing the human youngster attached to me.ā (Researchers sometimes call babysitters āaunts.ā Thatās precisely who they often are.)ā
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