We consider menopause a simple fact of life, but in reality, it’s actually very uncommon in the animal kingdom!
A study on killer whales seems to have helped researches find the missing puzzle piece in the case of the evolutionary mystery that is menopause.
Menopause is the chapter that ends most women’s reproductive lives, when menstrual periods end permanently, and they can no longer become pregnant. Women generally experience menopause between 49 and 52 years of age.
That means we, as humans, basically stop reproducing halfway through our lives, unlike the majority of animals around the world. Even our friendly companions, dogs and cats, have a lengthier reproductive life than us (when considering the difference in life expectancy).
Dogs do not experience menopause, although their cycles may become irregular and infrequent. Menopause has been observed in a few other species closer to our ecosystem (chimpanzees, or elephants), but the subjects have mostly been captive individuals; this making the results incomparable to what actually happens outside of captivity.
To get some conclusive answers, researches started exploring the post-reproductive lives of animals in the wild, with the study on killer whales being the true eye-opener on the matter!
Darren Croft of Exeter University shared a few different theories behind this atypical evolutionary trait, after studying killer whales for several years.
The “Evolutionary Accident” theory suggests that menopause is among one of the many accidents that stuck around, as evolution solidified its “survival of the fittest” rule.
This theory suggests that this trait occurred in our lineage sometime in our recent evolution, and we’ve been carrying it through generations.
However, Croft himself says that this theory is easily disproved simply by pointing out just how infrequently menopause manifests in the animal kingdom.
Menopause is more likely a post-reproductive stage of life that’s deeply embedded into our evolutionary journey for a reason.
But what is that reason?
The “Granny” theory is one of the earliest ideas meant to identify a cause for menopause.
Apparently, older females from species that experience menopause are programmed to stop reproducing just to help with raising their grand-kids.
So instead of pushing for more children of their own, they devote themselves to giving the next generation a better chance to reach adulthood, losing their reproductive abilities in the process.
The eldest matriarch of a killer whale clan has been shown to call the other whales from mile away, guiding them to the best salmon hunting spots. A granny never lets her grand-kids go hungry!
The main downside of the “granny” theory is that is doesn’t account for all the other species that lead the pack as the elders of a group, but continue to breed (like elephants for example).
Although the “granny” theory explains how the post-reproductive life of menopausal species looks like, the “Reproductive Conflict” theory explains why certain species stop reproducing in the first place.
A study on several orca mothers that were near menopausal age revealed breakthrough information! These orca mothers were paying a higher price for reproducing, when in competition with their younger daughters.
The offspring of middle-aged females were more likely to die than those of their younger counterparts. This fact, along with the “granny” effect, lead menopause to becoming a thing in killer whale populations!
So just like humans, killer whales that have reached the menopausal stage of their reproductive life will start to look for a new purpose in life. A middle-age crisis if you will.
Most species in the animal kingdom are innately driven by their fertility. Females from these species are basically doomed once they become infertile. And that’s because they no longer contribute to the main goal of the group: propagating the species!
Whichever theory is correct, in the case of menopause, finding a purpose beyond your fiercest instincts is an amazing thing to observe in the wild.
Women have full control over their reproductive lives. And we see the “granny” effect as the most endearing hypothesis. But it’s remarkable to see this type of complex behavior taking place in such a few select other species.
One would imagine that an elder orca will be more successful in passing along its genes by continuing to reproduce later in life. It invests energy into giving her grandchildren better odds. It accepts the fact that her late-in-life offspring would suffer facing their younger competitors. An amazing decision-making process seen from the animals we share this evolutionary anomaly with!