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.
Grandmothers get cranky if they don't get enough sleep.
( z1 cranky :domain ( z2 person :ARG0-of ( z3 have-rel-role :ARG2 ( z4 grandmother ) ) ) :condition ( z5 get :polarity - :ARG0 z2 :ARG1 ( z6 sleep :ARG0 z2 :ARG1-of ( z7 have-quant :ARG3 ( z8 enough ) ) ) ) )