Genes, Brains, and Human Potential The Science and Ideology of Intelligence

148 INTELLIGENT DEVELOPMENT

dynamics rather than a linear command sequence. Development, that
is, constitutes a responsive, intelligent system, with many compensa-
tory mechanisms and creative options in an ever- changing environment.
Th is pro cess has many other striking consequences for understanding
the construction of form and individual diff erences.

UNIFORMITY AND VARIATION IN DEVELOPMENT

Canalization

Of course, we do know that human individuals, like all animals, do vary
genet ically. But not randomly so. Remember that it is a basic princi ple of
natu ral se lection that this ge ne tic variation will be reduced for forms and
functions impor tant to adaptation. Genes that do not supply the goods
needed for survival are simply eliminated as their bearers fail to reproduce.
Th is is why any two humans are genet ically more than 99  percent identical.
However, even 1  percent of genes is still a lot of genes to vary, especially
when we remember that each gene consists of thousands of single nucleo-
tide polymorphisms that themselves can vary. What are the implications
of that for development?
In fact, the evolved intelligent system of development usually copes
with such ge ne tic variation perfectly well by using alternative resources
and/or diff er ent routes of development. Biologists have noted that the
development of impor tant forms and functions is remarkably durable,
or “robust.” And, as mentioned in chapter  4, many genes can be elimi-
nated without aff ecting function. So the physical bumps and shocks of
the environment that might be expected to disrupt development seem to
have little eff ect in most cases. Development continues regardless.
In experiments in the 1940s, C. H. Waddington discovered that for
characteristics crucial for survival, development is strongly buff ered. Th at
is, fairly standard forms and functions appear in all individuals, regard-
less (within wide ranges) of variation in the individuals’ genes, or in the
environment during development. More broadly, Waddington realized
that there must be some layer(s) of regulation between genotype and
phenotype that keep development on a uniform course. He introduced
the concept of epige ne tics, meaning above or beyond the genes.

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