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

152 Educability and Group Differences
social stratification is based largely on education, occupation, and
income, the abler members of the society will tend to move
upwards and the less able gravitate downwards in the SES
hierarchy. In so doing, they of course take their genes for intelligence
with them. The high degree of assortative mating for
intelligence (correlations between spouses ranging from 0-40 to
0-60 in most studies) increases the segregation of genes for mental
ability and helps to maintain the substantial correlation between
SES and intelligence. Thus, social classes are breeding populations
differing in gene frequencies, especially for genetic factors related
to ability and very likely for the genetic component of those
personality traits which favor the development, educability, and
practical mobilization of the individual’s intellectual potential.
But there is considerable mobility between social classes which
works against their becoming castes. In fact, if social classes
rigidified into castes at some period in history, genetic intelligence
differences between them would most likely be reduced, since all
of the IQ variability arising within classes in each generation would
remain as within-class variance. A high degree of social mobility
correlated with ability, on the other hand, in each generation
‘converts’ a substantial proportion of the within-class variance to
between-class variance. Thus, classes separated by more than two
or three steps in the SES hierarchy can in time undergo wide
separation in the distributions of genetic factors related to
ability. This trend increases the closer we approach equality of
educational and occupational opportunity and the more that
SES mobility reflects ability factors rather than inequalities in
opportunity.
Burt (1959; see also 1943 and 1961b) has shown the distributions
in England of sons according to their own and their father’s social
class, when SES is grouped into three broad categories, as follows:
Father's
Status
Son's Adult Status
I II III Total
I (High) 51-7 34-5 13-8 100-0
II (Middle) 23-3 46-9 29-8 100-0
III (Low) 13-7 36-9 49-4 100-0