Killer whales and humans would seem to have little in common. We inhabit very different ecosystems, after all. Yet the two species share one unexpected biological attribute. Females of Orcinus orca and Homo sapiens both go through the menopause.
It an extraordinary aspect of our development. In contrast to the vast majority of animals on our planet, women and female killer whales stop reproducing halfway through their lives. Only one other species – the short-finned pilot whale (Globicephala macrorhynchus) – behaves this way.
The question is: why? For what reason do females of these three different species give up the critically important process of reproduction in middle age? According to Darren Croft of Exeter University, whose team has been studying killer whales for several years, there are many different theories. “Some have argued that it is an artefact that has appeared during our recent evolution and has simply persisted in our lineage,” he said. In other words, there is no specific reason for the menopause in humans. It is simply an evolutionary accident. However, Croft believes there is overwhelming evidence that the menopause is an evolved trait deep rooted in our past.
One idea to account for the deep-rooted evolution of this trait uses the concept of the “granny effect”: older females are programmed to close down their reproduction so they can devote themselves exclusively to the rearing of grandchildren. In doing so, they lose the ability to pass on their genes directly to one generation but gain because they can help the following generation to reach adulthood, thus promoting their genotype for the future, it is argued.