IQ gains, WISC subtests and fluid g: g theory and
the relevance of Spearman's hypothesis to race

Flynn JR.
Department of Political Studies,
University of Otago, PO Box 56,
Dunedin, New Zealand.
Novartis Found Symp. 2000;233:202-16; discussion 216-27.


IQ gains over time were calculated for each WISC (Wechsler Intelligence Scale for Children) subtest and the subtests ranked by size of gain. Verbal similarities led at 20 points per generation--larger than gains on Raven's Progressive Matrices. Similarities measures on-the-spot problem-solving (something akin to fluid g); verbal subtests that do not measure this show low rates of gain. WISC subtests were also ranked by their correlations with Raven's, the latter being used as a marker for fluid g. The r between the two hierarchies was calculated to approximate a correlation between IQ gains and fluid g. The result of 0.50 contrasts with the negative correlation between IQ gains and the g generated by factor analysing the WISC battery itself, which is generally viewed as predominately a crystallized g. In sum, it appears that human groups can make massive fluid g gains in a period too short to accommodate radical change in the speed and efficiency of neural processes. Moreover, once gains in intelligent behaviour over historical time are seen to be independent of brain physiology, does g really provide a criterion for assessing their significance? Finally, not only a measure of fluid g (which is highly heritable) but also inbreeding depression are shown to be correlated with IQ gains--gains overwhelmingly environmental in origin. Therefore, correlations between such genetically influenced factors and the size of the black/white IQ gap do not show that the gap has a genetic component.

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