Nikolai's response regarding Hardin and population growth got me thinking about this...
Here is an interesting read at ENN regarding family size, household wealth and evolution.
The research appears to be seeking an evolutionary explanation for slowing rates of population growth. We know that world population growth is slowing. i.e. population is growing, but not nearly as fast as it has in the past. The UN has predicted that world population will plateau by around 2050,
at a population somewhere between 7.4 and 10.6 billion people (best
guess is 8.9 B). This is despite significant increases in longevity and lower mortality rates due to advances in medicine and sanitation. The slowing of population growth is due to lower birth rates. People are deciding to have fewer children, mostly in developed countries.
The article summarizes the results of a study which attempted to test the hypothesis that having fewer children leads to future reproductive success for offspring due to the advantages of wealth. i.e. having fewer children conveys an evolutionary advantage, if having fewer, but richer children today increases the likelihood that your genes will multiply in the future.
I'm not sure I follow this line of reasoning, but in any event, the authors of the study did not find support for the hypothesis. However, there are a lot of economic reasons why parents in richer nations might have smaller families than parents in poorer nations. Can anyone think of these?
Here is more reading at the World Bank.
Here is a long report from the UN on population growth and predictions for the future.