Scientists have developed a theory called “the grandmother hypothesis”. The idea behind it is that mature women are needed to help younger women produce more children, by taking on a nurturing role for existing offspring when new babies come along. Anyone who has young children will probably agree that having a mother or mother-in-law nearby certainly makes this reproductive phase of one’s life a lot less stressful.
There is an alternative theory called the “reproductive conflict hypothesis”. This hypothesis suggests that younger women and mature women both in reproductive phases are competing for limited resources when pregnant, so nature favours the younger woman and menopause is triggered in her mother around the time the younger woman hits peak fertility. One apparent flaw in this idea is that mothers and daughters can live great distances apart and yet still the mother will enter menopause around a certain age, even if she is not “competing” with her daughter for “resources”.