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

Race Differences in Intelligence 111
population is shown to be in the range of environment below the
threshold of adequacy for full realization of genetic potential,
while the bulk of the w'hite population is above the environmental
threshold for the full development of genetic potential. The consequence
of this hypothetical state of affairs is that the reaction
range of IQ should be much higher in the Negro than in the white
population, and the heritability of IQ should be lower in the Negro
Extrem e F a ir Very
D eprivation Relevant Environm ent Enriched
Figure 7.6 Hypothetical frequency distributions of Negro and
white populations of the United States with respect to environmental
variables relevant to intellectual development. When
compared with Figure 7.5, which has the same abscissa, it illustrates
the hypothesis that many Negroes may be reared in environmental
conditions that do not permit the development of genetic
intellectual potential to the same extent as in the white population.
than in the white population. In other words, this hypothesis shows
the bulk of the Negro population to be located in that part of the
environmental scale that makes the most difference in mental
development.
This seems to be a plausible hypothesis. But it has been legitimately
criticized. Bereiter (1970, p. 294), for example, points out
that there is no strong evidence for the threshold hypothesis and
that, at the time it was presented (Jensen, 1968a, 1969a), the only