In Elizabeth Gilbert’s book Committed, she writes mostly about marriage but devotes some of her words to aunthood and its role in human populations across time and place:

… here’s an astonishing fact that I discovered in the margins of my
research on marriage: If you look across human populations of all
varieties, in every culture and on every continent (even among the
most enthusiastic breeders in history, like the nineteenth-century Irish,
or the contemporary Amish), you will find that there is a consistent 10
percent of women within any population who never have children at all.
The percentage never gets any lower than that, in any population
whatsoever. In fact, the percentage of women who never reproduce in
most societies is usually much higher than 10 percent—and that’s not
just today in the developed Western world, where childless rates
among women tend to hover around 50 percent. …

In any case, the number of women throughout history who never
become mothers is so high (so consistently high) that I now suspect
that a certain degree of female childlessness is an evolutionary
adaptation of the human race. Maybe it’s not only perfectly legitimate
for certain women to never reproduce, but also necessary. It’s as
though, as a species, we need an abundance of responsible,
compassionate, childless women to support the wider community
in various ways. Childbearing and child rearing consume so much
energy that the women who do become mothers can quickly become
swallowed up by that daunting task—if not outright killed by it. Thus,
maybe we need extra females, women on the sidelines with undepleted
energies, who are ready to leap into the mix and keep the tribe supported.
(190-191) Continue reading →