I'm reading a book at the minute called 'The descent of madness: Evolutionary Origins of Psychosis and the Social Brain' by Jonathan Burns. I thought I'd summarise some of the theories in the book as to how schizophrenia came about, for the principle reason that it's very bloody interesting.
Some evolutionary thinkers have posited that schizophrenia is a recent disorder which is a modern response to the stresses of the industrial and technological age. Burns argues against this and claims that there is evidence of schizophrenia from early human history.
So, how and why did schizophrenia evolve when it has such a maladaptive nature? It's certainly not being selected out because the phenotype still persists with a similar rate of incidence across the human race.
The Adaptionist Programme has a solution for this problem of mental disorders in that it views them as behavioural traits which evolved due to an advantage for the the individual in the 'ancestral environment', however, now, in a world which has changed and become psychologically stressful, a mismatch is created between the evolved trait and the modern environment.
The persistence of the phenotype can also be explained by taking into account the fact that psychotic illness has a continuum on which schizophrenia is a severe end of the spectrum, because of this other phenotypes on the genetic spectrum could harbour particularly adaptive traits. Genetically related but unaffected individuals who share some of the milder features of the illness may possess some kind of evolutionary advantage and hence the phenotype would linger.
The hypotheses above are plausible by Jonathan Burns claims he has a better solution:
Our hominid ancestors evolved a sophisticated neural network supporting social cognition and adaptive interpersonal behaviour (in other words the social brain). This has been identified, using functional imaging, to be comprised in the fronto-temporal and fronto-parietal cortical networks. Psychosis (and schizophrenia in particular) are characterised by functional and structural deficits in these areas and hence the term 'social brain disorders' are fitting.
Schizophrenics display abnormalities in a wide range of social cognition tasks such as emotion recognition, theory of mind and affective responsiveness and as a result individuals with schizophrenia find themselves disadvantaged in the social arena and vulnerable to the stresses of their complex social environments.
So, since there is such evidence to support that the areas which comprise our 'social brains' are the same regions which contribute to the disorder of schizophrenia when functional and structural deficits are present it becomes clear that schizophrenia exists as a consequence to the complex social brain.
This is a desirable hypothesis due to the fact that it does not rely on a Cartesian model of an isolated ethereal mind separated from body and environment, and instead concentrates on a physically and socially integrated construct of mind, embodied in the living world.
I'd just like to add a small disclaimer which says that I'm not an expert in schizophrenia or pretty much anything I'm writing about here (I haven't even finished the book) so sorry if I've got anything hideously wrong. Please tell me. I'll revisit this with extra thoughts on the subject once I have finished the book.
In other news and on the subject of evolutionary psychology here's a really fun and ridiculously geeky thing I found: