Is the relationship between fertility of parents and children really weak?

The relationship between fertility of parents and children has been designated as "weak" by most investigators. This paper reviews the evidence over the past century and argues that, even allowing for problems with available data sources, the relationship was probably close to zero for pre-transitional populations. However, over time, the relationship has tended to become more substantial and is now of a similar order of magnitude in developed countries as other widely used explanatory variables. Possible mechanisms for the observed relationship are discussed, especially the roles of socialization and inherited factors. The types of data used are compared to the scientific questions posed, and the limitations of the common comparison of married-mother/married-daughter pairs are considered. Finally, some evidence from recent large-scale surveys in Britain and the United States is presented to show changes over recent periods and the relative effects of sibship size of fathers and mothers.