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

Recapitulation 363
care of the mother and undesirable conditions attending birth.
These conditions prevail in the poorer segment of the Negro
population and probably contribute to the incidence of neurological
handicap among Negro children. All of the causes of high
fetal loss, however, are not understood, for there are some populations
which, even when living under disadvantaged conditions
have shown lower rates of fetal loss and infant mortality than are
found today in the white majority - Jews and Orientals, for example.
There is now some evidence that the degree of genetic heterogeneity
of the fetus’s ancestors is directly related to the probability
of fetal loss, and thus genetic factors may be involved even in this
seemingly environmental phenomenon (Bresler, 1970). Disadvantaging
forms of birth trauma such as anoxia, low birth weight and
prematurity are reflected in subnormal performance on infant tests
of perceptual-motor development. But large representative samples
of Negro children show no depression of scores on these tests and
generally perform at slightly higher levels than middle-class white
children. Prenatal and perinatal factors, though differing in Negro
and white populations, do not begin to account for such phenomena
as the six to eight times higher rate of mental retardation (IQs
below 70) in the Negro than in the white population. Unless one
hypothesizes the existence of genetic factors, the cause of the
mental retardation in the vast majority of cases must be categorized
as ‘unknown’ or ‘unidentified’.
SUMMARY
In view of all the most relevant evidence which I have examined,
the most tenable hypothesis, in my judgment, is that genetic, as
well as environmental, differences are involved in the average
disparity between American Negroes and whites in intelligence
and educability, as here defined. All the major facts would seem
to be comprehended quite well by the hypothesis that something
between one-half and three-fourths of the average IQ difference
between American Negroes and whites is attributable to genetic
factors, and the remainder to environmental factors and their
interaction with the genetic differences.
Educational Implications
If this hypothesis stands up under further appropriate scientific