156 INTELLIGENT DEVELOPMENTways, and with little correlation between ge ne tic and phenotypic varia-
tion. Nevertheless, the general public, as well as many scientists, still hold
on to the idea that diff erences in potential lie in diff erences already coded
in genes in the embryo. Th at view implies that diff erences in individuals
in impor tant functions are largely due to diff erences in genes. As we have
seen, though, things are far from being so simple.
In the case of the individual, the original cells are totipotent; in spite
of the same genes they have the same potential to become any kind of
diff erentiated cell for a par tic u lar organism. In the French fl ag model,
every cell has the potential to develop as white, blue, or red. Indeed, re-
cent advances in the laboratory prove that it is pos si ble to change virtu-
ally any cell type into another cell type—to recover their potential for
diversity. Th is is epige ne tic reprogramming, in which a developed spe-
cifi c potential is turned back to become a totipotent stem cell.^16
But what about diff er ent individuals? When people think of original
potential, what they really mean is how it diff ers from individual to indi-
vidual, with the implication that some will have more potential than
others for traits like intelligence. And those diff erences, they have been
told, reside largely in diff erences in the genes.
However, it is very diffi cult to describe potential in such simple terms,
as demonstrated by in vitro fertilization clinics. Th e clinics talk to anx-
ious would-be parents about “egg quality.” But the concept turns out to
be rather vague. In rare cases, worrying variation can be spotted as chro-
mosomal or other defects, usually vis i ble under the microscope in the
fi rst two or three days. Other wise, quality criteria consist of eye- balled
( under the microscope) physical features, such as cell number in the
three- day embryo, cell regularity and uniformity, or degree of any
fragmentation.
Indeed, most labs admit that any generalizations about quality made
from grading embryos are rather inaccurate. As one site puts it: “We see
some cycles fail aft er transferring 3 perfect looking embryos, and we
also see beautiful babies born aft er transferring only one low grade em-
bryo.” Th e best test of egg quality in fact seems to be female age. Much
the same applies to sperm quality.
What parents tend to worry about, of course, is “ge ne tic potential”—
usually for critical functions like brain and cognition. Th anks to the kind
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