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.
Infertile women do not contribute to child-rearing.
( z1 contribute :polarity - :ARG0 ( z2 woman :ARG1-of ( z3 impregnate ) ) :ARG2 ( z4 rear :ARG1 ( z5 child ) ) )