http://economix.blogs.nytimes.com/2011/04/07/the-case-for-having-more-kids/April 7, 2011, 9:00 am
The Case for Having More Kids
By DAVID LEONHARDT
Bryan Caplan, an economist at George Mason, is the author of �Selfish Reasons to Have More Kids,� which will be released this week. Mr. Caplan doesn�t believe everyone should have a lot of children. But he does say many parents and future parents should consider having more children than they are currently planning.
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Mr. Caplan: The central idea of twin and adoption research is that disentangling nature from nurture is hard. Our intuition isn�t very helpful. Yes, kids of college-educated parents know more words. But why? Maybe their upbringing is the reason, as you suggest. But babies from college-educated families might excel even if raised by high school dropouts, by learning a higher fraction of the words they hear, or spending more time reading.
So what does the twin and adoption data say? Language fits a standard pattern. Consistent with your skepticism, upbringing has a noticeable effect on the vocabulary of young children. But as children mature, this effect largely fades away. The Colorado Adoption Project found, for example, that 2-year-olds adopted by high-vocabulary parents had noticeably larger vocabularies. But as the kids grew up, their vocabulary scores looked more and more like their biological parents�. By age 12, the effect of enriched upbringing on vocabulary was barely visible.
Admittedly, there�s a sense in which upbringing is all-important: If a baby is raised by wolves, he won�t know any words. (There�s also a sense in which genes are all-important: If you had wolf DNA, you wouldn�t know any words either.) But twin and adoption research focuses on questions that are much more relevant for parents: how your child will turn out if you switch to another parenting style.
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Since, as Caplan explains, intelligence is highly heritable, it is especially important for smart people to have lots of children.
