Elementary, my dear Watson, the clue is in the genes... Or is it?

James Watson's contribution to the discovery of the structure of DNA in the 1950s and to the sequencing of the human genome half a century later cannot fail to excite all those fascinated by human development. Each day we learn more about genes and the human brain. As we do, there is a temptation to seek one-to-one relationships between (on the one hand) complex behaviours like altruism, aggression, intelligence or language, and (on the other hand) specific genes or locations in the brain. In a series of popular books, Steven Pinker (1994, 1997, 1999) has repeatedly supported such assumptions by using data from adult neuropsychology and genetic disorders. In this article I argue that the interpretation of such data is flawed. It is based on a static model of the human brain, ignoring the complexities of gene expression and the dynamics of postnatal development. I will illustrate this through studies of infants, children and adults with the genetic disorder Williams syndrome. Understanding the complex pathways from gene to brain to cognitive processes to behaviour is like a Sherlock Holmes and Dr Watson detective story, in which seemingly unimportant clues early in development play a vital role in the final outcome.

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