A 1999 article published in "American Psychologist" summarises much of his research. On the alleged genetic inferiority of Blacks on IQ tests, he lays out the argument and evidence for such a belief and then contests each point. He interprets the direct evidence—when Blacks are raised in settings that are less disadvantageous—as suggesting that environmental factors explain genetic differences. And yet, he argues that the environmental explanation gained force after the discovery that IQ scores were rising over time. Inter-generational IQ differences among Whites and across nations were larger than the Black-White IQ Gap and could not be accounted for by genetic factors, which, if anything, should have reduced IQ, according to scholars he references. He posits that the Black-White IQ score gap can be entirely explained by environmental factors if "the average environment for Blacks in 1995 matches the quality of the average environment for Whites in 1945."