Ed Yong in Not Exactly Rocket Science:
Last summer, I met Granny. I was on a whale-watching boat that had sailed south from Vancouver Island, in search of a famous and well-studied group of killer whales (orcas). Two hours after we set off, we started seeing black fins scything through the unusually calm and glassy water. We saw a dozen individuals in all, and our guide identified them by the shape of their fins and the white saddle patches on their backs. Granny, for example, has a distinctive half-moon notch in her dorsal fin.
Seeing her, I felt an intense and solemn respect. She is the oldest member of the group, perhaps the oldest orca on the planet. Her true age is unknown, but a commonly quoted estimate puts her at 103, which would make her a year older than the Titanic, and far more durable. Imagine all that she has seen in that time: the generations of her children and grandchildren; the countless pursuits of fleeing salmon; the increasingly noisy presence of fishermen, scientists and gawking tourists. Decades of knowledge and wisdom live in her brain. Ad that knowledge might explain one of the most unusual features of killer whale biology—their menopause.
Animals almost always continue to reproduce until they die. There are just three exceptions that we know of: humans, short-finned pilot whales, and killer whales. In all three species, females lose the ability to have children, but continue living for decades after. That’s menopause. Female killer whales go through in their 30s or 40s. Why? Why sacrifice so many future chances to pass on your genes to the next generation?