Factors affecting the fecundity and fertility of historical populations: a review.

Abstract

This article discusses some of the characteristics involved in determining family size in preindustrial i.e. noncontraceptive populations. Marriage age greatly influences family size; in preindustrial Europe marriage age went from 24 to a maximum of 29 years while it was lower in colonial New England where women married at 20-22. Thus it is not surprising that complete families were larger in colonial America with 7-9 children than in Europe with 4-6 children. Adult mortality during childbearing age was very high thus shortening duration of marriage which was only about 15 years in England but 29-33 years in colonial America. Duration of marriage in turn influenced parity. Age also directly influences fecundity either because of the increase of anovulatory cycles or because of decline in sexual activity. Fecundity is also affected by nutrition since the amount of stored body fat influences the onset of menarche. Undernourishment can indeed reduce the reproductive life span by contributing to later menarche and earlier menopause. Another significant determinant of family size is birth interval. Birth interval is determined by length of postpartum amenorrhea menstruation pregnancy wastage and gestation preceding the next live birth. Amenorrhea lasts much longer in breastfeeding mothers in all types of society thus decreasing fecundity. Cultural taboos such as abstention from coitus during predetermined periods also influences the length of birth intervals. Infant survival is linked to breast feeding through maternal nutrition; the hard work and undernourishment prevalent in preindustrial societies may have caused maternal depletion and its possible effects on childs health. The frequence intensity and duration of the infants suckling are also assoicated with milk production and thus to infant nutrition. Secondary sterility and subfecundity are also determinants of family size affecting men as well as women. Variables such as poor diet and widespread diseases very common characteristics in preindustrial countries also affect fecundity. On the other hand psychological diseases such as depression or stress may be a cause of subfecundity in industrialized societies.