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

88 Educability and Group Differences
high heritability means, among other things, is that a large part
of the variance in status on the trait at maturity is, in principle,
predictable at the moment of conception. That is to say, it is
determined by genetic factors. If we take into consideration
prenatally determined constitutional factors as well as the genetic
factors, most of the variance in adult status for highly heritable
characteristics like height, and to a slightly lesser degree intelligence,
is theoretically predictable at birth. When something is highly
predictable, it means nothing less than that it is predetermined.
This is an unpopular but nevertheless accurate meaning of
predictability. Predictability does not necessarily imply, however,
that we have any control over the predetermining factors, nor does
it necessarily imply the contrary. Although the correlation between
Stanford-Binet IQ at age 2 and at age 18 is not higher than about
+ 0*3, meaning that less than 10 percent of the variance in IQs
at age 18 is predictable from a knowledge of IQs at age 2, heritability
estimates indicate that some 70 to 80 percent of the variance in
adult IQs is, in principle, predictable or predetermined at the
time of conception.. At each year from birth on, more and more
of the predictable, predetermined aspect of the phenotype becomes
manifest. This assumes, of course, that environmental influences
throughout the course of children’s development are no more
variable than the actual environments in which the vast majority
of children in our society are reared. It is the consolidation factor,
C, in our simplex model which corresponds to the genetic and
constitutional determining factors. Thus we should expect from
this model that the heritability of IQ should increase from infancy
to maturity as more and more experience is consolidated. This has
been found in the increase of parent-child correlations from
infancy to later childhood; such correlations strongly reflect
heritability when the children have had no contact with their
natural parents (because of adoption) with whom they show
increasing correlations in intelligence as they mature, as was
shown by Honzik (1957).
Also, from our model we would expect the squared loadings of
che first principal component of the simplex matrix (P.C.I in
Tables 3.1, 3.2, and 3.3) to approximate the amount of variance
accounted for by individual differences in the C factor at any
cross-section in the time scale of development. This can be clearly
shown with simulated data in which the C values are of course