The mystery of menopause is a step closer to being solved thanks to research on killer whales.
In a study conducted by the Universities of Exeter and Cambridge has found a link between pilot whales, killer whales, and humans. They are the only three known species where females stop having menstruation after a certain age in their lifespan.
But even though all these three species have different structures, the study shows that in each case, females become increasingly genetically related to those they live with as they get older. And because of this, older females get motivated to do what is best for survival.
This study is the first, which explains why these species specifically are the only ones in which females tend to stop reproducing while they still have decades left to live.
“It’s always been puzzling as to why only humans and toothed whales have evolved menopause, while females in all other long-lived species continue breeding until late in life,” says Dr. Michael Cant, from the University of Exeter’s School of Biosciences (Cornwall Campus).
Even though the social behaviors of the three menopausal species are very different, their social systems mean females become more related to those around them as they get older. This makes females of our species, and those of killer whales and pilot whales, to evolve into menopause and late-life helping.
Humans are said to have evolved in groups in which young females leave their group to find a mate. This means they started their reproductive lives in families to whom they were genetically unrelated. However, later in life, when their offspring start to breed, they become more genetically related to those around them and have the option to stop reproduction from helping raise their grandchildren.
But this argument does not explain menopause in pilot whales or killer whales, where both sexes remain in their family groups throughout their life, but sometimes come together with other groups to mate. Its research shows that females become more closely related to infants in the group as they get older even when they are different social animals.
Usually, in other mammals, males tend to leave their group to breed rather than females. In such cases, older females are selected for continuity of breeding rather than giving up the breeding and raising contrast with humans and menopausal whales. In other long-lived mammals it is typically males who leave the group to breed, and females who stay with their mother. According to the research, in this case, older females will be selected to continue breeding rather than give up reproduction to help raise grandchildren.
This is the first time that we can see a link between species who menopause and have a valid explanation of why they evolved in this way or which is responsible for menopause but somehow gives us the idea as to why it is restricted to only a few species.