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

Between-Groups Heritability 147
Environmental variables hypothesized to account for some of the
between-groups difference are most unamenable to empirical
evaluation if they have little or no variance within at least one of
the groups and preferably both. When there is no within-group
variance in some factor, it is impossible to demonstrate a correlation
between that factor and IQ. If, for example, we hypothesize
that all Negroes experience a feeling of ‘alienation’ which depresses
H e rita b ility W ith in Groups (h * )
Figure 5.1 Heritability between groups as a function of average
heritability within groups for different values of within-group
genetic correlation (p) for two populations which differ phenotypically
by one standard deviation.
the IQ, we must show that ‘alienation’ is, in fact, correlated with
IQ. Unless variance in ‘alienation’ can be measured in some way,
there is no way of showing its correlation with IQ. If there is
variance, a correlation coefficient significantly greater than zero
will establish a relationship, but not necessarily a causal one.
Clearly the most potentially fruitful environmental hypotheses we
can investigate are those involving environmental factors which
have the highest correlations with IQ (or other measures of mental
abilities) within population groups. If a causal connection between
the environmental factor and IQ can be established, so much the