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

358 Educability and Group Differences
of its genes from Caucasian ancestors. Methods exist for probabilistically
estimating the proportion of Caucasian genes in a hybrid
Negro population and in individuals in such a population, based
on a dozen or more genetic polymorphisms (various proteins in
the blood) with known frequencies in West African and European
populations. If in environmentally homogeneous samples there
was a higher correlation between IQ and the proportion of Caucasian
ancestry than between IQ and socially visible racial characteristics
which can be objectively measured, such as skin color and
interpupillary distance, a strictly environmental hypothesis of the
IQ difference would not be upheld. If maternal half-siblings were
used in such research, even prenatal environmental effects would
be controlled. The method used in this way could probably be
more definitive than any other method or combination of methods
presently available, short of long-term longitudinal studies in which
all environmental factors could be rigorously controlled throughout
the course of development from the time of conception.
DEFICIENCIES OF MAJOR ENVIRONMENTAL HYPOTHESES
Those environmentalist hypotheses of the Negro-white IQ difference
which have been most clearly formulated and are therefore
subject to empirical tests are the only ones that can be evaluated
within a scientific framework. The most frequently cited environmentalist
hypotheses which are sufficiently clear to be put to an
empirical test and which already have been tested have not
proven adequate to the explanatory function they were intended
to serve. A number of lines of such evidence cast serious doubt
on purely environmental and cultural theories of the racial IQ
difference.
Socioeconomic Differences
Matching or statistically controlling socioeconomic status (SES)
of racial samples does not wipe out IQ differences, although on the
average it reduces differences by about one-third. The racial
difference increases with increasing SES level when the IQs being
compared are those of children classified according to their parents’
SES. This finding is hard to rationalize along purely environmental
lines, but it is predictable from the genetic principle of filial
regression toward the population mean. Children of high SES