Evolutionary explanations of Schizophrenia

Stevens and Price (1996) developed this hypothesis. The characteristics of schizoid personality serve an adaptive function under certain conditions, including mood changes, bizzarre beliefs, hallucinations, delusions and strange speech. A 'crazy' individual may act as a leader and enable one subgroup to split off from a main one, a valuable function at times when the main group has become too large to be optimum. As group sizes increase, so does predation, difficulties in finding enough food, and intragroup rivalries. 

An extreme example is the cult of Jonestown where the one cult leader moved a significant number of people away from the population to live in 'peace and harmony', resulting in the death of 918 people who he persuaded to drink substance laced with cyanide, which they all knew would kill them. 

One extreme view is that of Crow (2000) who suggested that sz is the price humans pay for language. Crow also said that language has clear adaptive advantages in terms of enabling users to engage in precise communicartion. He proposed that a genetic mutation led to the development of language but also predisposed individuals to mental illness. Crow argues that a disorder like sz involves a breakdown in the brains internal liguistic controls. Szs often believe they are hearing voices and/or may use atypical language. 

In some individuals, language may not be lateralized (located in the left hemisphere, where it normally is) and this disrupts certain mechanisms of language e.g. to distinguish thoughts from speech output that he generates and the speech input he receives and decodes from others resulting in sz. 

Crow's hypothesis is interesting and is supported by the finding that there is reduced lateralisation of language in szs (Mitchell and Crow 2005). It is also true that szs involve language abnormalities

• - It is not clear how the deficient language skills of szs is related to evolutionary success.
• - Most of szs symptoms have little to do with language e.g. lack of emotion & motivation, disorganised movements, social impairment
• - Most genetic occur over hundreds of thousands of years, making it unlikely genetic changes leading to language and to sz occurred rapidly. 

There is some evidence that taking cannabis can lead to sz. Cannabis raises levels of dopamine in the brain and could trigger psychotic episodes. 

Henquet et al (2005) in a meta analysis found that young, heavy users of cannabis were twice as likely as non users to develop sz. 

Evaluation

+ Several studies have found a link

- It seems likely increased risk only occurs in young people who have a genetic predisposition 

- People with early sz symptoms might take cannabis as a form or self-therapy to deal with their negative experiences, suggesting that the cannabis is not a causal factor.