“There are one or two variations to this rule: a post-reproductive animal or human can afford to be totally altruistic from a genetic point of view. Grandmas and elderly spinster aunts have great evolutionary value. (We shall return to the role of grandmothers in co-operative nurturing of children.) And the menopause gives a human mother more time to perform her child-rearing and educational role, freed from the duties of reproduction, which tend to limit her selfless streak.”