The fading relevance of the nature–nurture argument has recently been revived by the rise of evolutionary psychology. A more sophisticated understanding of Darwinian evolution (survival of the fittest) has led to theories about the possible evolutionary value of some psychiatric disorders. A simplistic view would predict that all mental illnesses with a genetic component should lower survival and ought to die out. ‘Inclusive fitness’, however, assesses the evolutionary value of a characteristic not simply on whether it helps that individual to survive but whether it makes it more likely that their offspring will survive. Richard Dawkins’s 1976 book The Selfish Gene gives convincing explanations of the evolutionary advantages of group support and altruism when individuals sacrifice themselves for others.A range of speculative hypotheses have since been proposed for the evolutionary advantage of various behaviour differences and mental illnesses. Many of these draw on ethological games-theory (i.e. the benefits of any behaviour can only be understood in the context of the behaviour of other members of the group). So depression might be seen as a safe response to ‘defeat’ in a hierarchical group because it makes the individual withdraw from conflict while they recover. Mania, conversely, with its expansiveness and increased sexual activity, is proposed as a response to success in a hierarchical tussle promoting the propagation of that individual’s genes. Changes in behaviour that look like depression and hypomania can be clearly seen in primates as they move up and down the pecking order that dominates their lives.The habitual isolation and limited need for social contact of individuals with schizophrenia has been rather imaginatively proposed as adaptive to remote habitats with low food supplies (and also a protection against the risk of infectious diseases and epidemics). Evolutionary psychology will undoubtedly increasingly influence psychiatric thinking – many of our disorders fit poorly into a classical ‘medical model’. Already it has helped establish a less either–or approach to the discussion. It is, however, a highly controversial area – not so much around mental disorders but in relation to social behaviour and particularly to gender specific behaviour. Here it is often interpreted as excusing a very male-orientated, exploitative worldview. Luckily that is someone else’s battle.