When I sit down to ponder about Schizophrenia one of the first questions that comes to mind is:
What are the evolutionary benefits to such a disorder?
Seeing as there is a universal prevalence rate of approxiamately 1.1% of the population, schizophrenia could not be due to chance mutations. Evolutionary psychologists claim that this standard prevalence rate implies that schizophrenia existed when Homo sapiens emigrated out of Africa. So with this long history of the disorder, nature had plenty of time to extinguish this maladaptive disorder. Yet, the mental illness continues to plague the globe at an unwavering rate; even instances in remote populations, such as Australian Aboriginals and Nepali villagers, remain constant. Hence, schizophrenia must have evolved over time for some mysterious purpose or as a negative byproduct of an evolutionary benefit.
One of my first conclusions points to the fuzzy line between mental illness and ingenuity. Perhaps schizophrenics are on the opposite spectrum of geniuses. Depending on the genetic factors and environmental influences, modified brain chemistry may lead individuals to either gain creative insight into particular fields or result in hallucinations, delusions, affective blunting, or various other schizophrenic symptoms.
I looked further into potential theories of the evolutionary basis of schizophrenia and discovered the following theories:
Schizophrenia as an evolutionary advantage to the group:
- Religious based delusions that enhanced religious rituals ( perhaps justifying the hallucinations of religious prophets)
- group-splitting hypothesis of schizophrenia: schizophrenic individuals were usually prominent enough (tended to show signs of leadership) in tribes that their symptoms would result in breaking up the group into smaller units.
- Protective function: the symptoms of schizophrenia forces the individual to be in a state of constant alertness, which enhanced territorial instincts.
Schizophrenia as an evolutionary by-product:
- Crow’s theory: psychosis is a result of cerebral asymmetry, which evolved in conjunction with human’s language ability; the core deficit in psychosis is a failure of segregation of right from left hemisphere functions.
- An extreme variant of normal social skills or a trade-off for complex social cognition
- Horribin’s theory: negative alterations in the neuronal membrane phospholipid metabolism, or fatty acids, that lead to enhanced creativity may result in schizophrenia. He implies that schizophrenia is a whole body disorder, not just a brain problem. (To read more about this interesting theory refer to The madness of Adam and Eve: How schizophrenia shaped humanity by Horribin (2001)).
Schizophrenia as an evolutionary advantage on the individual level:
- Reproductive advantage: schizophrenics have a higher resistance to many things: to shock, visceral perforation, high doses of histamine, insulin, thyroxin, and other physiologically active substances, as well as infection and many allergies.
- Physiological advantage: As Horribin’s claims, schizophrenia is a whole body disorder demonstrated through the unusual posture, gait, and body shape of diagnosed individuals. The high fever of schizophrenic individuals provides further evidence to Horribin’s theory.
- Psychological advantage: there is no evidence that links psychosis, particularly schizophrenia, with creativity (which disproves my hypothesis!)
Schizophrenia as an evolutionary advantage at the kin level:
- Schizotypal personality: schizophrenia falls on a genetic continuum where relatives show schizotypal traits and features, even when they are not diagnosed as schizophrenic.
- Milder forms of schizophrenia tend to exhibit more divergent thinking
So, perhaps the increased severity in developed countries is a biological reaction to the norms and cultural standard society reinforces. Perhaps Western culture encourages the schizotypal personalities, which lead to the genetic mutations and thus cognitive and emotional impairments that are characteristic of schizophrenia.
Source: Nichols, Catherine (2009). “Is there an Evolutionary Advantage of Schizophrenia?” Personality, Psychopathology, and Original Minds. 46,8 : Pages 832-838.