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

348 Educability and Group Differences
are related to the genetic heterogeneity of the ancestral gene pools
of the American Negro.
The genetic interpretation of Bresler’s findings is highly
technical and cannot be examined here, but it has been tested and
reliably demonstrated in numerous animal experiments (referenced
by Bresler, 1970). Briefly, more distantly related gene pools have
greater genetic imbalance between gene loci on the chromosomes;
the loci for certain genes do not match up properly, so that if the
two alleles required for the production of an enzyme have undergone
evolutionary translocations on the chromosomes, the enzyme
controlled by a particular gene may not be produced and therefore
cannot make its necessary contribution to the normal development
of the growing embryo or fetus. Different genes become important
at various stages of development, and some genetic imbalances
will prove lethal while others will be sublethal but can cause
developmental anomalies of varying severity. The effects have
been demonstrated, for example, with frogs, all of the same species,
but distributed over a wide geographical range. Bresler (1970,
p. 24) summarizes some of the findings from these experiments, in
which genetic crosses are made between frogs of the same species
collected from varying geographic distances:
1. The hybrids between members of adjacent geographical
territories tended to be normal in development and morpho-
logy-
2. The greater the geographical distance between parental
combinations in eastern North America, the more retarded
was the rate of development, the greater were the morphological
defects in the hybrids, and the fewer were the normal
individuals.
3. The greater the geographical distance between parental combinations,
the larger was the percentage of eggs which failed
to develop properly.
4. The further apart in geographical distance . . . the members
were collected from, the earlier in development did reproductive
wastage occur.
What about heterosis, or hybrid vigor, which usually results
from outcrossings Heterosis results when there are dominant and
recessive genes involved in a characteristic. Outcrossing increases
the likelihood of heterozygotes, and if the dominant genes are