EVOLUTIONARY AND WEALTH FLOWS THEORIES OF FERTILITY - EMPIRICAL TESTS AND NEW MODELS

Caldwell's wealth flows theory of human family size predicts that children in high-fertility societies provide net economic wealth for parents. Models of fertility derived from evolutionary biology expect that all organisms will be designed to invest more resources in their offspring than they receive from them. These competing predictions were subjected to independent tests in three traditional societies in lowland South America. The results clearly showed that children produced no more than 25 percent of their total caloric needs between birth and 18 years of age and that grandparents worked hard to support their grandchildren rather than vice versa. No support for Caldwell's theory was found. A new theory of fertility decisions based upon evolutionary ecology is proposed, focusing on tradeoffs between fertility and the reproductive value of offspring, and between care of, and resource investment in, children.