There is no cross-culturally stable impact of income on fertility, and changes in values are more important, according to a recent review of published literature by a demographic expert.
Lyman Stone, director of the Pronatalism Initiative at the Institute for Family Studies, tackled the widely held beliefs that poor people have more babies than rich people, and that alleviating economic costs will not increase fertility because the poor will have babies anyway. However, he found that because different cultural groups often have unique income levels, efforts to correlate income and fertility are often “deeply misleading”.
“Global fertility decline was kicked off almost entirely by normative and cultural processes, not strictly economic ones. The effect of income on fertility is not even remotely consistent across cultures or even across times”.
He adds: “When whole societies become richer, they do not necessarily have fewer children. Once we control for the basic problem of cultural stratification, the supposed link between low income and high fertility, or high fertility and low income, largely disappears”.