Even those who believe I have provided a coherent interpretation of massive IQ gains over time may wish for something better. The fact that the differences between our minds and those of our ancestors are subtle only makes the task of reading them more difficult. If only we could get into a time machine and go back and study our ancestors directly.

Colom, Flores-Mendoza, and Abad (in press) may have given us the next best thing. They did a study of children aged 7 to 11 years in Brazil. They compared an urban sample from the city of Belo Horizonte (tested in 1930 on the Draw-a-Man test) with both an urban sample from that city (tested in 2002) and a rural sample (tested in 2004). Over seventy-two years, urban children had gained 17 IQ points, but the contemporary urban–rural gap was even larger at 31.5 points. Present-day urban children and rural children were also compared on Raven's Coloured Matrices and the WISC Arithmetic and Digit Span subtests. The urban–rural gap was 31 IQ points on Raven's and 15 points on the WISC. The rural children came from Americaninha, a district without hospitals, banks, postal service, and TV (only 8 percent of homes have electricity).