The tendency of families in wealthier societies to produce fewer children is hard to explain in evolutionary terms. A study of Swedish families examines the paradox, known as demographic transition.
One model proposed to explain the phenomenon holds that fewer offspring receive more resources, making them more likely to have offspring themselves. The model posits that richer people might have fewer children, but would ultimately have more descendents over subsequent generations.
Not so, say Anna Goodman of the London School of Hygiene and Tropical Medicine and her team. In their analysis of 14,000 Swedish people born between 1915 and 1929 and their descendents, small family size predicted greater socioeconomic success in children, grandchildren and great-grandchildren, particularly among families that already had high socioeconomic status. But small family size did not translate into greater reproductive success among the descendants.
Proc. R. Soc. B http://dx.doi.org/10.1098/rspb.2012.1415 (2012)