In my recent post on whether children are normal goods (demand for children increasing with income), I dodged questions around the effect of education. Most recent studies into the effect of income on children control for the level of education, as did Bryan Caplan in his analysis that found a positive correlation between income and children in the United States.
I am torn over whether controlling for education gives us meaningful information. Education clearly has a negative effect on fertility. Education takes time, which reduces the time available for children. However, education increases income. If education is simply an investment of time to earn income in the same way that labour is, then maybe we should not control for it in determining the effect of income on number of children. Rather, we should combine the education and labour time and examine the opportunity cost and effects of the entire investment.
Of course, education serves purposes other than increasing income. It is a signal in itself. But this only raises the question of why someone would undertake this costly education to obtain income or send a signal, which is in turn used to attract a mate, when the ultimate effect is less children.
In part, we need to consider that mating markets are two-sided. While the man might increase his marketability through education, the market in which he then shops is full of educated women who are strongly affected by the time expended on education. There is also the issue of the timing of income, with many years of student life preceding the income boost. By the time the income arrives, the eligible partners are older. But why then would these potential partners not assess their mate’s expected income? Is there too much uncertainty?
Ultimately, an evolutionary perspective does not hand you the answer on a plate. Humans are now exposed to an environment so far from their environment of evolutionary adaptedness that many of our actions can only be considered sub-optimal from the crude perspective of biological fitness. The rationale for the investment in education will likely have evolutionary elements, such as acquisition of resources and signalling to mates and allies, but the motivations driving those actions do not deliver fitness benefits like they once did. The proximate objective of attracting a high quality mate does not guarantee the ultimate objective.