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

REAL GENES, REAL INTELLIGENCE 127

Other research suggests that the variety of alternative transcripts is
strongly associated with levels of evolutionary complexity. It makes the
obvious point: it is diffi cult to claim that this or that variation in a trait is
caused by this or that gene when a gene can be associated with so many dif-
fer ent products. But that is by no means the end of such complications.

OTHER PROTEIN MODIFICATIONS

Th e protein products of the genes are further modifi ed by system dynam-
ics in a variety of other ways, all depending on current context. Th ere are
only about twenty- two thousand genes in the human genome, but at least
a hundred thousand protein products are known. Such is the plasticity of
gene transcription and translation.
A particularly well- studied example is ubiquitination. Ubiquitin is a
small regulatory protein that binds to gene products in a number of
diff er ent ways. Th e binding can speed up degradation of the product or
change its location in the cell, its level of activity, degree of interaction
with other proteins, and so on. However, the form and activity of ubiqui-
tin is itself under the regulation of the signaling/transcriptional networks
just mentioned. Indeed, such modifi cation to proteins aft er translation
from the mRNA has evolved to become critical for animal, including
human, learning. It helps coordinate the changes in connectivity aft er
activity between brain cells.

RNA REGULATORS

In the standard model of development and variation the variable gene codes

are transcribed into mRNAs that are translated into correspondingly vari-

able proteins (resulting in correspondingly variable phenotypes). We now

know, however, that mRNAs have numerous functions other than serv-

ing as protein- coding templates. For example, they can alter the speed of

initial transcription in a feedback loop; improve transport of products

around the cell; and increase rate of decay of the mRNA product (the pep-

tide or protein) itself, aff ording more rapid responses to external signals.

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