Whale of a Cousin

Only three species on planet Earth have evolved the process of going through menopause—wherein females continue to live many years after they have stopped reproducing. Two of these species are whales (killer whales and short-finned pilot whales) and the third is humans. For these three menopausal species, females quit reproducing in their 40s, but can continue living into their 90s. 

Why are these three dissimilar species so similar in this way? What could be the reason for menopause—or what is its advantages for a species—when the usual drive for a species to survive is to reproduce as much as possible, as long as possible, and pass their genes into the future? (If there was no reproductive advantage to menopause, it would not have evolved.) What use can old females have to their whale pods or human societies? Do we really need “old ladies”?

None of the great apes—with whom we share about 99% of our DNA—go through menopause. Old female apes stay fertile all their lives and live only to about 40 years of age. So again the question arises, why do old-lady whales (much more distant from us, DNA-wise) and humans quit having babies? I find it fascinating that it’s just the whales and us.

The answer of “why menopause?” seems to be due to the social structures that have evolved for these two types of mammals—structures that are unique to killer whales, short-finned pilot whales, and Homo sapiens. There are likely two answers as to why menopause is useful: (1) keeping female elders around is important because they can share their knowledge and expertise of how to find food and safety, thereby continuing to help the species thrive, and (2) by giving up having more offspring, they can avoid reproductive competition with their daughters—so as to give the grandchildren of these long-living species a better chance at life. 

Continued survival of the species is what it’s all about. Resources in a group’s environment may be limited, so overcrowding does not help the species stay fit and robust.  Older females who quit having babies help to limit crowding. Additionally, useful and novel gene permutations (which younger females are more likely to create) must be allowed a chance to propagate into the future, which creates evolutionary progress.

So the grandmother humans and whales willingly and wisely step aside, passing the reproduction game on to their daughters. Crones can be an invaluable source of community knowledge and tradition. 

Males of these species can also possess valuable knowledge, but the females are more socially connected and pass more information on more effectively.