Menopause in Animals
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Menopause is stage that women go through where they are no longer able to reproduce. This time is associated with a host of uncomfortable symptoms like hot flashes and mood changes. In the animal kingdom menopause is not very common. But before you throw your pet turtle out the window out of spite, consider this- some animals like the Pacific salmon have no post-reproductive life meaning that they literally die after the cannot reproduce anymore and most animals die shortly after they lost the ability to reproduce. So with this perspective, perhaps menopause in humans is not the end of the world (unlike the poor Pacific salmon). But back to the subject at hand, what is the deal with animals and menopause?
Humans are the most predisposed species toward menopause. The vast majority of the animal kingdom does not get menopause. Some sources say that only other species that get menopause are killer whales and pilot whales. Menopause is less famously found in some species of fish, bird, and primates as well as elephants, opossums, and lab mice. It is interesting to study menopause in killer whales and pilot whales because unlike primates they live a long time after they are no longer able to reproduce. So where apes generally do not live long after menopause, a killer whale can live 40 years after menopause and a pilot whale can live 30 years after menopause. Since their life spans are closer to humans, they are more interesting to study. However, it is inaccurate to say that the other species listed above do not go through menopause because while there is no definitive definition of menopause, most agree it simply “the permanent cessation of ovulation” meaning the period where animals stop ovulating. The animals above do in fact stop ovulating at some point and thus go through menopause as well.
Ok, so we have determined that animals technically do go through menopause, but do they feel symptoms like humans? We do not know, because these symptoms are very difficult to measure and generally studies on menopause require people reporting the severity and number of hot flashes. With animals such as whales we like the requisite physiological knowledge to determine whether they have hot flashes.
There is an interesting question of why animals go through menopause to begin with. From an evolutionary perspective all species have evolved to successfully transmit their genes by reproducing. If the species is not successfully transmitting its genes, then it means that the species is going to disappear. No longer being able to reproduce seems like it goes against evolution because without reproduction there is no transmission of genes to the next generation which makes menopause a bit of puzzle. A common answer to this riddle is that older females go through menopause to protect the interests of their children and grandchildren. As animals get older the risks associated with childbirth increase. So while propagating your genes directly through reproduction is good, if you and your child die in the child birth process nothing is accomplished. So instead, it may be more beneficial to protect your genes by protecting and nurturing your grandchildren and the children you already have. In the killer whale population, one killer whale will go off to mate in another pod, but immediately return to their original pod. A killer whale’s pod is a family unit. So by staying alive longer and not risking death by giving birth, the menopausal whale can look after its pod family and thereby protect the genes it has already propagated.
So to recap, most animals do not go through menopause. This is probably because their post-reproductive life spans are very short i.e.- the time they live after menopause. For the species that do, menopause may be nature’s way of ensuring grandma does looks after the offspring she has rather than risk dying by trying to have more!