I would like to add briefly three further perspectives to the debate between David Kingdon and Alan Young, ^{Reference Kingdon and Young1} on biological mechanisms and clinical psychiatry. First, it is unsustainable to contend, as Kingdon does, that biological approaches are based on the pursuit of physical causes for mental disorders. Causal processes in biology are both physical and intentional, ^{Reference Bolton and Hill2} and modern biological psychology and psychiatry are making major contributions to our understanding of the interplay between them.

Second, as Young brings out, developmental studies show how social processes affect biology, and biology modifies susceptibility to environments. Animal studies find that early adverse experiences have long-term behavioural effects and an impact on biological processes such as gene expression. ^{Reference Francis, Diorio, Plotsky and Meaney3} Thus, links between quality of parenting in early life and subsequent adaptation may be mediated genetically. ^{Reference Francis, Diorio, Plotsky and Meaney3} Animal and human studies find that environmental effects on depression vary depending on genotype. ^{Reference Caspi, Sugden, Moffitt, Taylor, Craig, Harrington, McClay, Mill, Martin, Braithwaite and Poulton4} Studies of adult depression find that child maltreatment history modifies the role of interpersonal processes, the presence of structural differences in the brain, and treatment outcome, all highly relevant to clinical practice. ^{Reference Teicher, Andersen, Polcari, Anderson and Navalta5,Reference Nemeroff, Heim, Thase, Klein, Rush, Schatzberg, Ninan, McCullough, Weiss, Dunner, Rothbaum, Kornstein, Keitner and Keller6} In studies of children, assessments of biological consequences of social experience, such as hypothalamic–pituitary–adrenocortical reactivity during parent–child conversations, are integral and essential. Developmental psychopathology would not have got off the ground based on the assumptions presented by Kingdon.

Finally, there is, in my view, a problem that is not to do with the conceptual and empirical issues debated by Kingdon & Young. Investigations of treatment outcomes, for example, in relation to genotype or maltreatment history, or genotype by maltreatment history, could be conducted within clinical practice but are very rare. As research funding, at least in the UK, becomes increasingly compartmentalised into different types of research such as ‘health services’, ‘trials’, ‘basic sciences’, who will fund the studies that cross these boundaries and bring biology into the clinic to the benefit of patients?