Not too many animal species exhibit the quality known as menopause, the (typically middle-aged) part of a female’s life where she begins to stop menstruating. To scientists’ understanding, the quality is only known to exist in three mammal species on Earth, humans included.
One other species known to exhibit these qualities are killer whales, and it has really baffled scientists to no end to figure out why this is such a limited quality. As a result, researchers have spent time studying killer whales to learn more about their lifestyle in an attempt to find just what might be causing menopause in whales.
Image Credit: TheyreBornFree
According to a paper published in Current Biology by behavioral ecologist Darren Croft of the University of Exeter and colleagues, killer whales probably exhibit menopause as a direct result of the competition for reproduction that goes on between older mothers and their younger, much more able-bodied, daughters.
“Our previous work shows how old females help but not why they stop reproducing,” professor Darren Croft explained in a statement. “Females of many species act as leaders in late life but continue to reproduce, but this new research shows that old females go through the menopause because they lose out in reproductive competition with their own daughters.”
Since older killer whales assume the responsibility of training and taking care of a large group of whales in a pod, they have more important things to worry about than reproduction, like ensuring the safety of their members. They hardly have as much time or patience for reproduction, whereas younger daughter whales are hormonally struck and ready to go.
That aside, there’s also another very important piece to the research: bearing children at such a late age can be detrimental to an older killer whale’s body, increasing the chances of mortality. As their body is aging and becoming more brittle with age, just as a human’s does, the younger whales in their prime are much better suited for reproduction, so passing the torch makes sense from a survival point of view too.
“It's easy to think that an older female will pass on their genes better by continuing to give birth in late life,” study co-author Dr Daniel Franks from the University of York said. “But our new work shows that if an old female killer whale reproduces her late-life offspring suffer from being out-competed by her grandchildren. This, together with her investment in helping her grandchildren, can explain the evolution of menopause.”
The idea would suggest that evolution has played a big role in the development of menopause, and such reasoning could also be attributed to many other mammal species that also exhibit this quality. Because the meaning of life is to live or die trying, the species has simply found a way to increase the odds of survival by passing reproducing down to much more able-bodied younger females, allowing the older females to worry about more important things, while still surviving.