The so-called "grandmother hypothesis", based on studies of African hunter-gatherer groups, suggests that infertile women are vital for successful child-rearing despite being unable to produce children themselves.
The "grandmother hypothesis says only fertile women are vital for child rearing
( z1 say :ARG0 ( z2 thing :ARG1-of ( z3 hypothesize ) :mod ( z4 grandmother ) ) :ARG1 ( z5 vital :domain ( z6 woman :mod ( z7 fertile ) :mod ( z8 only ) ) :purpose ( z9 rear :ARG1 ( z10 child ) ) ) )