Fertility and wealth in Sri Lanka: are children normal goods?

The paper by Weerasinghe and Parr resurrects a longstanding debate over the causal role of wealth in fertility reductions of the past centuries (1). Malthus, who did not foresee any negative correlation between wealth and fertility, wrote, "That population does invariably increase where there are the means of subsistence, the history of every people that have ever existed will abundantly prove" (2). For Malthus, the desires of the rich are just like those of the poor. Why then would wealthier people, who can have more of anything they want, have fewer children? He basically believes that all human beings like to have sex and will take any opportunity to start engaging in sex and reproduction as early and as often as they can. Malthus's unified account of human motivation is a very satisfying feature of his theory. His theory does appear to hold true in his own era. There had been fluctuations in the 'means of subsistence' prior to Malthus time, and the historical data on these populations indicate that they did indeed seem to behave the way that Malthus theorizes. Galloway describes over 100 years of population dynamics in Rouen, France, prior to 1787 and finds that abundant grain harvests significantly increased the numbers of marriages and births with opposite effects in bad times when grain prices rose (3). The Sri Lankan findings that wealth and fertility are negatively correlated challenge us again to explain how economic prosperity can be associated with lower fertility, without sacrificing a unified account of human motivation such as the one that Malthus set forth? Wealth can be used for proxying lifetime income and ought to correlate with the opportunities of earnings and socioeconomic status of women. Finding a negative correlation between fertility and economic status is hardly new, having been documented repeatedly in developed-country data (4-8). The contribution of Weerasinghe and Parr is to leverage asset data from a developing country into a wealth index that permits assessment of fertility patterns by wealth in a non-western setting. Heretofore, most studies of socioeconomic status and fertility in developing countries used parental education or urban-rural residence to assess socioeconomic status (9). A recent exception is work by Montgomery et al. which uses living standards data from Ghana, Guatemala, Jamaica, Pakistan, Peru, and Tanzania to test the effect of expenditure per adult and education of women to predict children ever born (10). In the study of Montgomery et al., economic status significantly reduces fertility for urban populations in all countries, except Peru. Economic status increases fertility for rural populations in all countries, except Jamaica. Unlike the study of Weerasinghe and Parr, significant effects of schooling on fertility remain for Montgomery et al., despite the inclusion of the economic status indicator. The Sri Lankan study in this issue of the journal is a welcome addition to the empirical literature on economic status and fertility. From a theoretical perspective, the old debate continues regarding how to account for a negative correlation between wealth and fertility. Weerasinghe and Parr offer a set of three explanations that could be consistent with an underlying positive effect of income on fertility: * Wealthier people know more about contraception than poor people do * Wealthier people face higher opportunity costs to raise children * Wealthier people do not need children much to support them in their old age A fourth explanation cited by the authors would overturn Malthus's unitary theory of motivation: * Wealthier people have different tastes and preferences about the quantity and quality of children Malthus anticipated none of these obstacles. In his world, children were without exception a normal good--a consumer durable *. The more money a person had, the more children a person would have. Humans in Malthus' day played by the same rules governing all birds and beasts--more resources equalled more biological fitness. …