Abstract
In 1970, Brown offered note on the division of labor. Her observation was that - across cultures - if a task interfered with child-rearing, then that task would be given to men. If a task did not interfere with child-rearing, then that task could be included in the set of chores assigned to women. A reasonable extension of her note would be that if a group's women, as a class, were performing tasks incompatible with child-rearing, then the fertility rates of that group's women would be decreased. A cross-cultural survey of current demographic indices re-affirms Brown's note. Data are presented which indicate that, as more of a group's women perform tasks which are incompatible with child-rearing, the lower the fertility rate of that group's women. As a corollary, there are systematic cultural evolutionary pressures for groups with higher fertility rates to replace or displace groups with lower fertility rates.