Recent studies have discovered one thing that humans and killer whales have in common. The females of both species go through menopause. Apart from these two, there is only one other species whose females stop reproducing when they reach middle age.
This sounds like an interesting claim, since these two species (Orcinus orca and Homo sapiens) have this aspect in common, while differing in many others. The third species behaving this way appears to be more similar to killer whales than humans. It is the short-finned pilot whale (Globicephala macrorhynchus).
What seems to bother us is the question why this happens to our species and to so many different others it does not. Older theories claimed that there was no specific reason for which female humans go through menopause. They regarded it like a mere accident in our evolution. However, Darren Croft, professor at Exeter University, has a different opinion.
One of his theories state the “granny effect”. This implies that older females stop reproducing because they devote themselves to their grandchildren. They can no longer pass their genes directly, but look out for the survival of their genotype to a larger extent, by helping their grandchildren reach adulthood.
However, Croft suspected that this was not the whole explanation. As seen in other animal populations, older females can act as leaders of their own packs and still reproduce. This is why they reverted to the analysis of killer whale populations.
They focused on a group of whales led by an almost 100 years old matriarch who stopped reproducing around the age of 40. While the matriarch proved to be the true leader, the analysis of females approaching menopause age was the most conclusive.
They found that older females went through menopause because of the reproductive competition with their younger daughters. The offspring of older mothers is 1.7 times more likely to die than that of younger mothers. Therefore, an older female does not deliver better genes than a younger one, it is the other way around. This is why they stop competing with their children and devote themselves to their grandchildren.
This theory can be extended to humans as well. It explains perfectly the role of menopause and the purpose of post-reproductive life, answering the questions on why females live so long even after they stop reproducing.
Image Source: Wikimedia Commons