The Economist reports here on a paper that only reinforces the case:
[W]hen poor economies start to grow, these disparities widen. The fertility rate of the whole country starts to fall but the families of the richest quintile get smaller faster than the families of the poorest quintile. In other words, the rich lead the process of demographic change, not the poor who have the most to gain and who, you might have thought, would find it easiest to reduce family size (because it seems a smaller step to have six, rather than seven children, than it is to have one, rather than two). The rich presumably find it easiest to control family size because they have the best access to family planning and their daughters are the most likely to be educated. This process goes on while economies have an income per head of between about $2000 and $5000. Between about $5000 and $10,000 a head, the three income quintiles in the middle start to reduce their family size faster. In other words, the middle class starts to catch up with the rich, presumably because they are getting access to family planning and wider female education, too. Then, by $10,000 a head, family size is falling by roughly equal amounts in every quintile: the poor have caught up with the rich and middle class, and fertility is falling across the board.
This paper says something new about demography by showing the relationship between income and fertility. It says something new about inequality by showing that there is a correlation between it and income in poor countries. And it has something interesting to say about public policy, since the findings would support the case for smoothing out the initial increase in inequality by encouraging the two things which help reduce fertility among the poorest quintile: family planning and female education.
Worth remembering the next time you hear the Vatican claiming that it is a force for ‘social justice’.