Economics inverse Darwinism

The Chicago Boyz blog babies and market signals discusses the modern resource allocation dilemma of children and the choice between self-financial preservation and the less academic species preservation. The blog discusses the factors in reproduction on an economic scale and the resulting conditions. It further examines the median population, of course not everyone fits perfectly into the average. This blog is evaluating the consequences of childrearing through the opportunity costs, such as children result in less education and income for parents. Typically for the mothers it results in less income, and for a single parent situation, the market signals would be there, and would demand decisions on profit or children, but I think most don't want children by themselves. Yes, to some extent there is a Darwinism effect in choosing between how much education and income weighted against the gene pool, however I think whether it's self or species preservation, it's survival of the fittest, and then there's welfare.