The cohort studies discussed by Gavin Francis often confirm what everyone already knows: that (statistically speaking) a person born into disadvantageous circumstances is likely to be disadvantaged through life (LRB, 2 June). The addition of DNA collection and analysis to these studies is a recent phenomenon, which Francis hopes will deliver a deeper understanding of the interplay between genes and environment. I suspect this will prove optimistic. We already know that the genetic contribution to most of the common chronic diseases – including stroke, type-2 diabetes, heart disease, osteoporosis, chronic lung disease, chronic kidney disease and dementia – is surprisingly small. Genetic studies in this area generate great masses of data and any number of ‘statistically significant’ results. Very often the effect of a particular genetic variation is small, there is no plausible explanation, and when different cohorts are examined the results can’t be reproduced. When genetic thinking is applied to such hard-to-define traits as personality, behaviour, lawlessness and intelligence, the danger is that great volumes of white noise will be generated. Yet, as Jonathan Latham and Allison Wilson have pointed out, politicians, corporations and researchers are all partial to research into genetic determinism: politicians because it reduces their responsibility for ill-health and social disadvantage; corporations because it diverts blame; and researchers because funding for this type of research is relatively easy to obtain.

Tim Cundy
University of Auckland