Here’s yet another reason why females are weird: menopause. During their 40s, women permanently lose the ability to have children, but continue to live for decades. In doing this, they are virtually alone in the animal kingdom. From a cold evolutionary point of view, why would an animal continue to live past the point when it could pass on its genes to the next generation? Or let’s put it another way: why don’t they keep on making babies until they die? Why does a female’s reproductive lifespan cut out early?
Ironically, I decided to search for the answer myself. One of the most popular explanations, first proposed in the 1966, involves helpful grandmothers. Even if older women are infertile, they can still ensure that their genes cascade through future generations by caring for their children, and helping to raise their grandchildren. There’s evidence to support this “grandmother hypothesis” in females: It seems that mothers can indeed boost their number of grandchildren by stepping out of the reproductive rat-race as soon as their daughters join it, becoming helpers rather than competitors.
But now, human females are not the ONLY organisms that go through this. Emma Foster from the University of Exeter has found similar evidence among one of the only other animals that shows menopause: the killer whale. Killer whales, or orcas, become infertile during their 30s or 40s, but they can live well into their 90s. Individuals stay within the pod they were born in, which gives older mothers plenty of chances to help their children and grandchildren. The same is true for humans and pilot whales – the only other species known to have a long menopause. Your Thoughts?