NEW YORK – Killer whales and humans are among the only animals known to experience menopause.
Female orcas go through two main stages of life: a fertile phase and, in their many post-reproductive years, a leadership phase. By studying these whales, scientists are starting to shed light on the natural history of menopause — why it emerged and how it benefits a species.
This is an area of research that can’t be done with captive whales. The older females in the wild are leading large pods in the act of hunting. Captive whales can’t form pods or hunt.
That’s why some scientists say they were not sorry to learn that Sea World would end its captive breeding program. Even if there were no moral issue, the hot area of research has shifted from studying the way whales learn and solve human-constructed problems to studying whales as they live their natural social lives, said animal behavior expert Darren Croft.
“There’s a fascinating social system in which sons and daughters don’t disperse,” Croft said. Instead of striking out on their own when they grow up, they stay with their mothers.
Pods are matrilineal, composed of old females, their offspring and their daughters’ offspring. There aren’t many old males, Croft said, because there’s a huge disparity in life expectancy, with males living to about 40 and females up to around 100.
At about the same age that the males expire, female killer whales go through menopause. The only other female mammals known to have long post-reproductive lives are pilot whales and humans. Most other animals reproduce until they are near death.
Fatherhood is not part of whale life. Neither is bonding between mates. Males will mate with females in neighboring pods but stay with their own families. The supreme, permanent bond in killer whale society is between mothers and their sons. All offspring stay with their moms throughout life, but the mothers put more energy into caring for the sons. Research in 2012 showed that males tend to die shortly after their mothers die. In 2015, researchers published observations that the older females lead their pods to find the most promising hunting grounds.
These observations are shedding light on an evolutionary puzzle regarding menopause. In Darwinian terms, success is about propagating genes, and shutting down reproduction for an extended period of time would seem to pose a disadvantage.
However, in evolution, there are different ways to succeed, and it’s not always a matter of quantity of offspring. Otherwise we’d all be breeding like bunnies. In some species, individuals are more likely to propagate their genes if they have fewer offspring but invest more in their survival and their success in reproducing. One of the most popular ideas to explain human menopause is the so-called grandmother hypothesis, which posits that older women keep promoting their genetic legacies by helping with grandchildren. In whales, it looks like the older females help the whole pod, which is made up of their kin.
Wild killer whales also behave very differently depending on where they live. Some are permanent residents of an area; others form transient populations. Some eat salmon, others sea mammals — and they use different hunting strategies. It’s a little like cultural differences, Croft said.
On the decision to stop breeding whales in captivity, Sea World, scientists and animal rights activists are in agreement. Where the scientists agree with Sea World and disagree with some activists is in the decision not to free the current population of 28 captive whales.
The scientists say you can’t dump captive whales into the ocean and expect them to know how to survive. And it’s not just about finding food. Whales are social animals and may be even more stressed and miserable in isolation than we humans are.
The star of “Free Willy” went through extensive survival training before being released into the wild. But he was never able to integrate himself into a pod and he died after a couple of years, at age 27. For orcas, it seems, survival training is no substitute for a mother.
Faye Flam writes about science, mathematics and medicine.
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