Author's reply

Douzenis is concerned that adding evolution will make psychiatry narrowly biological in a way that excludes values. However, my article makes no claim that proximate and evolutionary approaches make up the whole of psychiatry, it says only that ‘biological psychiatry is making full use of only one half of biology’. ¹ Applying this additional biological knowledge to psychiatry should not exclude values. In fact, it offers a scientific foundation for addressing the very difficulties Douzenis mentions. It is fundamentally different from 19th-century evolutionary applications to medicine. ² It is an antidote to mindless reductionism. It helps to solve the problem of defining disease, ³ and to explain why psychiatric nosology is inherently problematic. ⁴ Furthermore, profound advances in understanding human moral capacities, with important implications for psychiatry, are coming from evolutionary analyses of their origins and functions. I encourage those who share Douzenis’ concerns to consider how evolutionary approaches can help us better understand our patients as individuals and provide personalised treatments that go far beyond analysing genes and prescribing drugs.

I am delighted that Treffurth finds my approach laudable, but dismayed that she seems to think my article is about evolutionary psychology. Evolutionary biology has vastly more to offer psychiatry than just evolutionary psychology, a field not mentioned in the article. I share Treffurth's concerns about the difficulties of reaching firm conclusions about the adaptive significance of traits; this is challenging science. However, most working biologists find little value in philosophical arguments about whole fields and generalisations about the study of adaptations. Using historical, comparative, and other evidence to assess hypotheses about past events poses challenges in geology and cosmology, as well as in evolutionary biology. Generalisations about the difficulties are not very helpful. Examples like the one provided do not undermine the enterprise, they illustrate how such hypotheses can be tested. We will come to better methods, not by disparaging whole areas of work, but by pursuing specific questions in depth with evidence.

The fields of animal behaviour, behavioural ecology, and evolutionary genetics offer well-developed frameworks for understanding phenomena of core importance to psychiatry, such as the origins and functions of the capacities for emotions, attachment, and social behaviour. Darwinian medicine offers explanations for why natural selection has left us vulnerable to diseases. ⁵ My argument is simple: basic knowledge from these fields is useful in psychiatry. Unfortunately, they are connected to psychiatry by only a few bridges. ⁶ I hope readers will explore and build more.