"IQ and Income Inequality in a Sample of Sibling Pairs from Advantaged Family Backgrounds" by Charles Murray, in The American Economic Review (May 2002), 2014 Broadway, Ste. 303, Nashville, Tenn. 37203.

How much more egalitarian would America be if every child grew up in an intact two-parent family, free of the modern-day plagues of illegitimacy, poverty, and divorce? Not that much, claims Murray, a fellow at the American Enterprise Institute and coauthor of the controversial Bell Curve (1994).

From the National Longitudinal Survey of Youth, which began in 1978, Murray carved out a "utopian sample" of 733 sibling pairs. Their parents were married and stayed together for at least the first seven years of their children’s lives. They were also relatively affluent (median income $64,586, in year2000 dollars). In other words, these children enjoyed major advantages. Only one significant difference divided them. In each pair, one sibling had "normal" intelligence (an intelligence quotient between 90 and 109), while the other had an IQ outside that range, either higher or lower.

By the time the siblings reached their thirties, Murray found, there were big differences in income. Those with "normal" intelligence had a median family income of $52,700, while their "bright" brothers and sisters had a household income of $60,500 and the "very bright" ones (120 IQ or higher) $70,700. The "dull" siblings (80–89 IQ), meanwhile, had a household median of only $39,400, and the "very dull" ones (below 80 IQ) just $23,600. These differences are only likely to widen over time, Murray adds.

These findings could point in several directions, toward policies that seek to equalize incomes or toward an acceptance of intractable inequality as the price one pays for freedom. But it won’t do for scholars to "live in a Lake Woebegone world where everyone can be above average," says Murray. Inequality in abilities is "a driving force behind inequality in the distribution of social and economic goods."