Killer whales show us the meaning of menopause

Despite its bad reviews, puberty has a sequel. And like most sequels, it is deeply unpopular.

The symptoms of the menopause include hot flushes, losing sleep, feeling sad or anxious, and finding that your bones lose their density and fall apart (or something like that).

All these symptoms are the body's way of saying "No more babies for you!". Yet it happens well before the sufferer has reached the end of life.

So why do we go through this process? What is the evolutionary advantage of middle-aged suffering? Surely breeding until we drop would pass on more of our genes, and therefore make more evolutionary sense.

Some scientists think they may have found the studying killer whales (Orcinus orca).

Pffft. They think they're all that. They're just giant dolphins.

Humans aren't the only species that stays alive long after it can reproduce. Menopause has been observed in other mammals too, including nonhuman primates, and cetaceans such as killer whales.

Female killer whales may live until they are 90 years old, but stop reproducing around the age of 40. Previous research has indicated that the post-menopausal females help the rest of the family group, using the type of wisdom that belongs to old mothers of any species. When times are tough, the old girls take charge, leading their relatives to where salmon is most abundant.

Perhaps keeping females around long after they can breed helps them pass on their wisdom. But that still doesn't explain why they don't just keep breeding.

On Boxing Day 2019, however, new research was published that gives a good argument why the not having babies bit is so important.

Like any good grandma, grandma killer whales help to raise the babies in the family. In humans, grandmothers often spend a lot of time and energy helping to raise grandchildren. The children, helped by their grandmas, survive into adulthood and have children of their own - perpetuating Grandma's genes.

Grandmothers help to increase the survival rate of their grandchildren.

The theory that individuals in a family help each other (even at a cost to themselves) in order to perpetuate the family bloodline is called kin selection. It explains a lot of altruistic animal behaviour, including why school bullies get beaten up by their victim's big brother or sister.

Grandmothers increasing the survival rate of their grandchildren is called the Grandmother Effect. It has been documented in humans, but never in another species...until now.

It turns out that a grandma killer whale's grandcalves are far more likely to survive if she is not currently rearing her own calf. While everyone helps rear the babies in a killer whale pod, grandmother killer whales are able to provide much more effective help if they are not too busy rearing their own flipper-biters.

Look, grandchild...this is how we pose for photographers

Killer whales, with their ridiculously attractive tuxedo wetsuits, and despite their playful malevolence, are loved by scientists and the general public. Researchers have accrued a great deal of knowledge concerning the biology and behaviour of killer whales, and some pods have been studied for so long that their genealogies are well-documented.

Such well-documented pods, inhabiting the waters around Washington State and British Columbia, were used in the whale menopause study. These pods feed on Chinook salmon (Oncorhynchus tshawytscha); when salmon numbers go up, killer whale mortality goes down.

In some areas, Chinook salmon are declining. Since the older killer whales know where the good salmon areas are, killer whales need their grandmas now more than ever.

The fact that killer whale grandmas are more able to help their grandcalves survive when they don't have their own calves to look after helps us understand a bit more about the menopause. Specifically, female killer whales (and also potentially human women) probably evolved to stop reproducing and focus their energies on the new generation.

In other words, grandmas stop having babies so they can help others rear their babies. Which says a lot about the selflessness of grandmas, and how much grandchildren rely on their wisdom and guidance.