Educability-and-Group-Differences-1973-by-Arthur-Robert-Jensen

230 Educability and Group Differences
(e.g., above or below the median in IQ, college entrance tests, gradepoint
average, etc.) and then determining the proportion of the lower
and higher groups showing the Duffy Fya ‘Caucasian gene’. This
test must assume no correlation between Fya and socially visible
features which could affect IQ and no correlation between Fya and
IQ in the white population. The feasibility of this proposal has been
questioned because the American Negro population probably has
not yet reached genetic (Hardy-Weinberg) equilibrium, so there
would probably be a great deal of genetic linkage of visible African
morphological features and blood polymorphisms. Controlling or
partialling out the visible racial characteristics would therefore also
partial out some of the IQ variance associated with the blood groups
used as an index of the degree of African-Caucasian admixture. If
it could be argued that the socially visible African features did not
themselves constitute an ‘environmental’ disadvantage that might
adversely affect mental development or performance on intelligence
tests, the proposal would have merit despite genetic disequilibrium
in American Negro racial hybrids.
4. If a 10 percent admixture of Caucasian genes raises the IQ of Negrowhite
hybrids by 10 points, one would have to assume a great deal
of genetic interaction or some kind of hybrid vigor to explain why a
100 percent admixture of Caucasian genes would raise the IQ only
about 15 points. If an admixture of Caucasian genes had the large
effect suggested by Shockley, one should expect there to be much
greater genetic variance among Negroes, and there is no evidence
of this. If anything, the evidence is for less genetic variance in the
Negro population. The 10-points IQ difference between Georgia
and California Negroes would therefore most reasonably be attributed
mainly to selective migration and environmental differences.
5. For further comments see the four critiques of the study by
Willerman et al. in the Letters to Science, 1971, 172, 8-12, with a
reply by Willerman et al.