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.
Childless ladies do not contribute to family structure.
( z1 contribute :polarity - :ARG0 ( z2 lady :ARG0-of ( z3 have :polarity - :ARG1 ( z4 child ) ) ) :ARG2 ( z5 structure :mod ( z6 family ) ) )