The world is a complex place. That is a truism, but perhaps complexity can be investigated rather than taken for granted. Think of the sorts of causal interaction one might regard as 'complex'. In 2002, Avshalom Caspi and collaborators published a widely reported study in which they concluded that the degree to which abuse in childhood increases the likelihood that men will exhibit antisocial behaviour later in life was partly dependent on the presence of a gene that appears to control the activity of an enzyme called monoamine oxydase A. Or consider an article published by the British Journal of Cancer in February, which suggests 'the intriguing possibility of a causal link between the molecular basis of breast cancer exemplified by p53 mutations and extreme deprivation'. Mutations in the p53 gene reduce the body's ability to suppress tumours: what is 'intriguing' here is the thought that poverty might interact with the gene in question, thereby worsening the prognosis for economically deprived cancer patients. Some studies have suggested that socioeconomic inequality somehow causes poor health - even among the reasonably well-off in unequal societies. These assertions of causal links between very different sorts of things - poverty and genes, inequality and health - are often contested, but they aren't especially unusual.

LRB 18 November 2010 | PDF Download