IIRC Jensen’s original argument was based on very high estimates for IQ heritability (>.8). When within-group heritability is so high, a simple statistical argument makes it very likely that large between-group differences contain at least a genetic component. The only alternative would be that some unknown environmental factor would depress all blacks equally (a varying effect would reduce within-group heritability), which is not very plausible.
Now that estimates of IQ heritability have been revised down to .5, the argument loses much of its power.
The Dickens-Flynn model, with high gene-environment correlations (the effects of genetic differences seem large because those genetic differences lead to assortment into different environments, but broad environmental change can still have major effects, as in the Flynn Effect) seems a very powerful indicator that environmental explanations are possible.
IIRC Jensen’s original argument was based on very high estimates for IQ heritability (>.8). When within-group heritability is so high, a simple statistical argument makes it very likely that large between-group differences contain at least a genetic component. The only alternative would be that some unknown environmental factor would depress all blacks equally (a varying effect would reduce within-group heritability), which is not very plausible.
Now that estimates of IQ heritability have been revised down to .5, the argument loses much of its power.
Bouchard’s recent meta-analysis upholds such high estimates, at least for adulthood. These are the figures listed on Table 1 (p. 150):
Did you type the number for Age 16 correctly? I can think of no sensible reason why there should be a divot there.
I uploaded Bouchard’s paper here. I also uploaded Snyderman and Rothman’s study here.
Yes, the figure is correct.
The Dickens-Flynn model, with high gene-environment correlations (the effects of genetic differences seem large because those genetic differences lead to assortment into different environments, but broad environmental change can still have major effects, as in the Flynn Effect) seems a very powerful indicator that environmental explanations are possible.