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 infertile women are not useful for child rearing
( z1 say :ARG0 ( z2 thing :ARG1-of ( z3 hypothesize ) :mod ( z4 grandmother ) ) :ARG1 ( z5 useful :polarity - :ARG1 ( z6 woman :ARG1-of ( z7 impregnate ) ) :ARG2 ( z8 rear :ARG0 z6 :ARG1 ( z9 child ) ) ) )