Assumptions about economies of effort in performance of tasks in the same production sequence and assumptions about constraints on women's geographic mobility due to nursing and child care are used to derive hypotheses about the allocation of tasks in the sexual division of labor in preindustrial societies. The hypotheses constitute a locational model of the division of labor by sex that makes predictions in the form of entailments: for one sex, doing task X entails doing task Y. The predictions of the locational model are tested using a new procedure for statistical entailment analysis applied to a body of data on fifty tasks in the 185 societies of the standard cross-cultural sample. Assumptions about constraints of nursing and the effect of supplementary feeding of infants on women's participation in task activities are also tested and found to be supported from the evidence on this sample.