The Bell Curve or The Bimodal Distribution?
By Arnold Kling
As recently as half a century ago, Americans across all classes showed only minor differences on the Founding virtues. When Americans resisted the idea of being thought part of an upper class or lower class, they were responding to a reality: there really was such a thing as a civic culture that embraced all of them. Today, that is no longer true. Americans have formed a new lower class and a new upper class that have no precedent in our history.
Murray is (in)famously the co-author of The Bell Curve. Its thesis is that intelligence matters for many outcomes. If intelligence is normally distributed and it largely determines one’s position in the class structure, then we should observe a class structure that also is normally distributed. Yet Murray today seems to be saying that the class structure is bimodal. At some point, I would like to directly ask Murray how he reconciles his new view with the bell curve.
The story I tell for bimodalism is mating behavior. When high earners marry high earners, class divisions will emerge. But this has implications for the IQ distribution. One would expect bimodalism to appear in the IQ distribution, with the children of high-IQ parents tending centered around one mode and the children of low-IQ parents centered around another.
What does the distribution of IQ scores among today’s Americans of age, say 15-24, look like? Are the 75th and 25th percentiles farther apart in terms of IQ than they were fifty years ago? If so, then I would think it is big news. If not, then I do not think that we can tell a story of class divergence in which IQ is a major factor.