Brad Delong points to this paper by Roland Fryer and Steven Levitt. (The whole working paper is available at Fryer’s site.)
In tests of intelligence, Blacks systematically score worse than Whites, whereas Asians frequently outperform Whites. Some have argued that genetic differences across races account for the gap. Using a newly available nationally representative data set that includes a test of mental function for children aged eight to twelve months, we find only minor racial differences in test outcomes (0.06 standard deviation units in the raw data) between Blacks and Whites that disappear with the inclusion of a limited set of controls. The only statistically significant racial difference is that Asian children score slightly worse than those of other races. To the extent that there are any genetically-driven racial differences in intelligence, these gaps must either emerge after the age of one, or operate along dimensions not captured by this early test of mental cognition. A calibration exercise demonstrates that the observed patterns in the data can be generated by a model in which there are extremely small mean differences in intelligence across races, but where there are large racial differences in environmental factors that grow in importance as children age.