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.
More than 11 studies were conducted on African hunter-gatherer groups.
( z1 conduct :ARG1 ( z2 study :ARG1 ( z3 group :mod ( z4 continent :name ( z5 name :op "Africa" ) ) :cxnsistof ( z6 person :ARG0-of ( z7 hunt ) ) ) :quant ( z8 more-than :op 11 ) ) )