As you point out, the research into the relationship between wealth and breeding by Mikko Myrskyla and his colleagues from the University of Pennsylvania suggests that the old rule of demography that people have fewer children as their countries get richer no longer holds true (“The Best of All Possible Worlds?” August 8, 2009). The research correlates the fertility rate in different countries and the United Nations’ human development index for 1975 and 2005. The index scores countries in terms of income, social equality, and provision for education and health. The old rule applies in the former year, but in the later year fertility turns up slightly for the highest values of HDI. At first glance, this is surprising. As you explain, there are two broad reproductive strategies: one is to produce as many offspring as possible and put them into an uncaring world in the hope that a few will make it, and the other is to have only a few progeny and dote over them so as to ensure their success. Although the research does not go into the relationship between wealth and breeding within individual countries, it is reasonable to guess that the poor follow the first of the above strategies, the middle classes the second, and that the rich make a small upward adjustment to the second strategy. Put this way, the results of the research are somewhat less surprising.