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

296 PROMOTING POTENTIAL

will be seen, these categories are not entirely mutually exclusive, but my

purpose is to illustrate, not exhaustively review.

EFFECTS OF SPECIFIC MATERIAL FACTORS

As with the genes, some research has focused on singular, fairly well-
defi ned, environmental components. Some specifi c deleterious factors
have been shown to aff ect development. For example, a wide range of
toxic agents can perturb cell metabolism with consequences for health
and development and, possibly, brain and cognitive functions.^6 Th ese
agents include heavy metals (e.g., lead and mercury) in food, water, or in-
dustrial wastes and carbon particles and gases from traffi c and industrial
fumes. Organic pollutants include hormone- disrupting pesticides, paints,
and preservatives.
Some incidents arising from side eff ects of phar ma ceu ti cal drugs have
been well covered in the media. Smoking during pregnancy has become
a big issue since the 1970s, and the abuse or misuse of other substances
during pregnancy is suspected to have eff ects on off spring.
Also in this category are gene mutations that can be incurred through
factors like UV radiation or radioactivity (i.e., gene mutations that are
themselves environmental in origin). Such cases have arisen from acci-
dents at nuclear power stations. Th ese can have unpredictable, but some-
times highly detrimental eff ects on wide- ranging aspects of development
and subsequent health and vitality. Th ose eff ects could be refl ected in
intelligence test results and school per for mance.
Conversely, there have been many attempts to identify unitary mate-
rial agents specifi cally promoting brain and cognitive development. For
example, some studies have suggested that breast- feeding boosts intelli-
gence of off spring in later life, even when other factors are taken into
account.^7 Some have reported associations with white matter volume in the
brain and IQ (white matter refers to the fatty sheaths around long nerve
fi bers that act as insulation and speed signal conduction; it contrasts with
the gray matter of nerve cell bodies).^8 It has also been suggested that the
par tic u lar fatty acids in breast milk promote cognitive development, mainly
through their eff ects on neuronal white matter and cell membranes.

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