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

Between-Groups Heritability 127
The preference for environmental explanations of group differences
reaches its zenith in a few studies. Gross (1967), for example,
compared two Brooklyn Jewish groups on a variety of cognitive
tests. The 90 Jewish boys, averaging about 6 years of age, came
from either Sephardic families (immigrants from Arabic or Oriental
countries) or Ashkenazic families (immigrants from Europe). All
their mothers were native-born and English was the household
language. All were middle class and lived in the same community.
Yet the Ashkenazic boys scored higher than the Sephardic boys
on the several cognitive tests and differed by as much as 17 IQ
points on the Peabody Picture Vocabulary Tests. The investigators
studied the family environments intensively for clues that could
explain the significant IQ difference between these two groups.
No significant differences could be found between the groups in
a host of family training and background experiences - except for
one item in the questionnaire of parental attitudes. Twice as many
Ashkenazic mothers said that earnings were ‘unimportant’ in their
desires for their children, and three times as many Sephardic
mothers said they wanted their sons to be ‘wealthy’. This single,
subtle attitudinal factor, then, supposedly explains the 17 points
IQ difference. There is no suggestion of the possibility that
Sephardic and Ashkenazic groups may have different gene pools
for many characteristics, including intelligence. The study is cited
by other writers (e.g., Havighurst, 1970, p. 321) as an example of
how subtle environmental differences can influence cognitive
development. It is interesting that no one has produced IQ
differences nearly as large as 17 points in non-disadvantaged groups
even by the most intensive training. Direct coaching on a particular
IQ test results in only about 9 or 10 points gain. Another zenith
of environmentalism: as an example of the effects of environmental
differences on IQ, Klineberg (1956) points to an IQ difference of
47 points (58 v. 105)1 between a group of rural Negro children in
Tennessee and a group of urban Negro children in Los Angeles.
Since the largest difference ever reported between a pair of identical
twins reared apart is 24 IQ points (Newman, Freeman &
Holzinger, 1937), it seems most improbable that a mean difference
of 47 IQ points would be attributable entirely to environmental
differences. It is, of course, not impossible, but it is highly improbable.
Preferences obviously do not always correspond to
probabilities.