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

220 Educability and Group Differences
racial differences in the distribution of intelligence. The research
possibilities implicit in this approach, however, are considerable,
but they depend upon genetically quite sophisticated methodologies
which have been recently suggested but have not yet been applied
to the problem. Earlier studies based on highly visible physical
characteristics as criteria for degree of racial hybridization were
virtually doomed to inconclusiveness.
American Negroes are racial hybrids. In 1926 Herskovits found
that 70 percent of a U.S. Negro sample reported having one or
more white ancestors (Herskovits, 1926), and in 1969, T. E. Reed,
a leading student of this subject, asserted that there are probably
no Negroes of pure African descent being born in the United
States today, unless they are born to African exchange students
(Reed, 1969a). Reed states that the American Negro usually has
‘between 2 and 50 percent of his genes from Caucasian ancestors,
and these genes were very probably received after 1700’ (Reed,
1969a, p. 165). All but a negligible proportion of the slaves brought
to the United States arrived between 1700 and 1800 and totalled
somewhat less than 400,000. Most of the introduction of Caucasian
genes into the American Negro gene pool occurred during the
period of slavery. Today the average percentage of Caucasian
genes in American Negroes is estimated, on the basis of blood
groups, at something between 20 and 30 percent. (These estimates
are based largely on population samples from northern urban
areas.) The evidence has been summarized by Reed (1969a). The
most representative estimate is probably that of Negroes in Oakland,
California, with 22 percent Caucasian genes. Due mainly to
selective migration, the percentages differ in various parts of the
country, being generally lowest in the ‘Deep South’ and highest
in the North and the West. The average in two counties in Georgia
is 11 percent. Representative samples in other localities are New
York (19 percent), Detroit (26 percent), Baltimore (22-31 percent).
Chicago (13 percent), Washington and Baltimore (20-24 percents.
Charleston, South Carolina (4-8 percent). Within each of these
Negro subpopulations there is considerable variability among
individuals in their percentage of Caucasian genes. The Oakland.
California Negro population, with its mean of 22 percent Caucasian
genes, has an estimated standard deviation of 14 percent (Shockley.
1970b), which means that the variability of the degree of Caucasian
admixture among the California Negroes is at least as great as the