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

50 Educability and Group Differences
growing organism, from the moment of conception, ‘interacts’ with
its environment is a mere truism. It says no more than the fact
that there are no organisms that have existed and grown without
an environment. The interactionist position is merely tantamount
to stating that the organism exists. But we already take this for
granted, and repeating the assertion that the individual is the result
of ‘the complex interaction of genetic and environmental factors’ is
simply stating the obvious. What the population geneticist actually
wishes to know is what proportion of the variation in a particular
trait among individuals is attributable to their genetic differences
and what proportion is attributable to differences in their environmental
histories. For the answer to this question one must turn to
the methods of quantitative-genetic analysis. The estimation of
heritability is among these methods. If it were true that environmental
factors so ‘interacted’ with the genetic factors, in the sense
intended by the ‘interactionists’, as to completely obliterate any
correlational or predictive connection between an individual’s
genotypes and phenotypes, the methods of quantitative genetics
are quite capable of revealing this. If our phenotypic characteristics
or measurements gave no clue as to the ‘genetic value’ of individuals,
it would mean that h2 would be zero, and, of course, the correlation
between phenotype and genotype (rpG = h) would also be zero.
But in fact, for human intelligence in our present society, most
estimates of h2 fall in the range from 0-60 to 0-90, with an average
close to 0*80 (Jensen, 1967, 1969a; Jinks & Fulker, 1970). So much,
then, for the abuse of the term interaction.
But now a clear distinction must be made between two theoretically
quite legitimate though quite different meanings of interaction.
The popular confusion of the two among behavioral scientists is
probably most due to a well-known and often reprinted article
‘Heredity, environment and the question “How” ’ by Anastasi
(1958). Anastasi points out that attempts to determine the proportional
contribution of heredity and environment to observed
individual differences in given traits (i.e., heritability estimation)
. . . have usually been based upon the implicit assumption that
hereditary and environmental factors combine in an additive
fashion. Both geneticists and psychologists have repeatedly
demonstrated, however, that a more tenable hypothesis is that
of interaction [4 references]. In other words, the nature and