Schizophrenia: An Schizophrenia: An Evolutionary Evolutionary PerspectivePerspective

By: Tanya KrausBy: Tanya Kraus

SchizophreniaSchizophrenia

a psychotic disorder characterized by a psychotic disorder characterized by major disturbances in thought, emotion, major disturbances in thought, emotion, and behaviour – disordered thinking in and behaviour – disordered thinking in which ideas are not logically related, which ideas are not logically related, faulty perception and attention, flat or faulty perception and attention, flat or inappropriate affect, and bizarre inappropriate affect, and bizarre disturbances in motor activity. Patients disturbances in motor activity. Patients with schizophrenia often withdraw from with schizophrenia often withdraw from people and reality into a fantasy life of people and reality into a fantasy life of delusions and hallucinations. delusions and hallucinations.

Positive/Negative Positive/Negative SymptomsSymptoms

Positive symptoms:Positive symptoms: Involves behaviour Involves behaviour that is not normally present in most that is not normally present in most people. (E.g. distortions, disorganized people. (E.g. distortions, disorganized speech, hallucinations, or delusions.) speech, hallucinations, or delusions.)

Negative symptoms:Negative symptoms: Involves Involves behavioural deficits that are not behavioural deficits that are not present in most people. (E.g. avolition, present in most people. (E.g. avolition, alogia, anhedonia, flat affect, and alogia, anhedonia, flat affect, and asociality.)asociality.)

Other SymptomsOther Symptoms

Many patients experience the Many patients experience the following as well as positive and following as well as positive and negative symptoms.negative symptoms.

Catatonia:Catatonia: Defined by several Defined by several motor abnormalities, which can motor abnormalities, which can include catatonic immobility or include catatonic immobility or waxy flexibilitywaxy flexibility

Inappropriate Affect:Inappropriate Affect: Emotional Emotional responses that are out of contextresponses that are out of context

Here’s Where the Evolution Part Here’s Where the Evolution Part Becomes Relevant…Becomes Relevant…

Unusual behaviours that strongly resemble Unusual behaviours that strongly resemble schizophrenia have dated back to schizophrenia have dated back to MesopotamiaMesopotamia

UniversallyUniversally, the prevalence rate of , the prevalence rate of schizophrenia is about 1%, which exceeds schizophrenia is about 1%, which exceeds common mutation ratescommon mutation rates

There is a strong genetic component (E.g. There is a strong genetic component (E.g. twin and adoption studies)twin and adoption studies)

Conditions such as schizophrenia have a long Conditions such as schizophrenia have a long history and a strong genetic base, meaning history and a strong genetic base, meaning evolutionary explanations must be evolutionary explanations must be acknowledgedacknowledged

Evolution PerspectivesEvolution Perspectives

Evolutionary perspectives can be Evolutionary perspectives can be divided into two groups:divided into two groups:

a)a) Theories that assume schizophrenia Theories that assume schizophrenia is a disadvantageous by-product of is a disadvantageous by-product of human brain evolutionhuman brain evolution

b)b) Theories that consider schizophrenia Theories that consider schizophrenia to have an evolutionary advantage to have an evolutionary advantage

Schizophrenia: Disadvantageous By-Schizophrenia: Disadvantageous By-Product of Human Brain EvolutionProduct of Human Brain Evolution

Theory #1:Theory #1: Farley’s argument that Farley’s argument that schizophrenia could be an extreme schizophrenia could be an extreme variant of normal social behaviour variant of normal social behaviour

Flaw:Flaw: This theory fails to explain This theory fails to explain why schizophrenia is comprised of why schizophrenia is comprised of both negative and positive both negative and positive symptomssymptoms

Disadvantages, Cont. Disadvantages, Cont.

Theory #2:Theory #2: Randall’s novel neural Randall’s novel neural pathways model…”biological trial and pathways model…”biological trial and error of connection would produce a error of connection would produce a range of behavioural variants, range of behavioural variants, including schizophrenia.”including schizophrenia.”

Flaw:Flaw: Denies the specific symptoms Denies the specific symptoms that occur in any given disorder, as that occur in any given disorder, as well as the maintenance of pathologywell as the maintenance of pathology

Disadvantages, Cont. Disadvantages, Cont.

Theory #3:Theory #3: Saugstad’s pathophysiological Saugstad’s pathophysiological model, which connects many frontal lobe model, which connects many frontal lobe disorders (E.g. schizophrenia, infantile disorders (E.g. schizophrenia, infantile autism), to delayed cerebral maturation. autism), to delayed cerebral maturation. Again, schizophrenia is viewed simply as an Again, schizophrenia is viewed simply as an outlier within the normal bounds of outlier within the normal bounds of variationvariation

Flaw:Flaw: It would be atypical for nature to It would be atypical for nature to produce such large numbers of distinct produce such large numbers of distinct phenotypes with reduced fecundity (Ability phenotypes with reduced fecundity (Ability to produce many children) to produce many children)

Disadvantages, Cont. Disadvantages, Cont.

Theory #4:Theory #4: Yeo and the Yeo and the developmental instability model developmental instability model of schizophreniaof schizophrenia

Flaw:Flaw: While being a very While being a very intriguing theory, it lacks any intriguing theory, it lacks any empirical evidence at this point in empirical evidence at this point in time. It should be considered time. It should be considered speculatively speculatively

Schizophrenia as an Schizophrenia as an Evolutionary AdvantageEvolutionary Advantage

Schizophrenia paradox:Schizophrenia paradox: “The “The discrepancy between high discrepancy between high prevalence rate and reduced prevalence rate and reduced fecundity”fecundity”

This doesn’t seem very adaptive, This doesn’t seem very adaptive, does it? does it?

There must have been some There must have been some evolutionary advantage to having evolutionary advantage to having schizophrenia…schizophrenia…

Advantageous Advantageous TheoriesTheories Theory #1:Theory #1: Huxley, Mayr, Osmond, and Huxley, Mayr, Osmond, and

Hoffer published the first model linking Hoffer published the first model linking schizophrenia to evolutionary concepts. schizophrenia to evolutionary concepts. (1964) Speculated that reduced fecundity (1964) Speculated that reduced fecundity was compensated by higher resistance to was compensated by higher resistance to allergens, shock, and infectionallergens, shock, and infection

Flaw:Flaw: No substantial evidence supporting No substantial evidence supporting this theorythis theory

Advantageous, Cont.Advantageous, Cont.

Theory #2:Theory #2: Kellet’s model suggesting Kellet’s model suggesting that certain characteristics found in that certain characteristics found in schizophrenia may have helped man’s schizophrenia may have helped man’s territorial instinctsterritorial instincts

Flaw:Flaw: This theory addresses only a This theory addresses only a small component of schizophrenia, small component of schizophrenia, providing no evolutionary explanation providing no evolutionary explanation for psychotic symptomsfor psychotic symptoms

Advantageous, Cont. Advantageous, Cont.

Theory #3:Theory #3: The schizophrenia gene could The schizophrenia gene could possibly benefit individuals who carry it but do possibly benefit individuals who carry it but do not have the disordernot have the disorder

Karlsson studied a population of schizophrenics Karlsson studied a population of schizophrenics in Iceland and discovered that first-degree in Iceland and discovered that first-degree relatives were twice as likely to be members of relatives were twice as likely to be members of creative professions than the general populationcreative professions than the general population

Flaw:Flaw: Providing an accurate association Providing an accurate association between psychiatric conditions and creativity between psychiatric conditions and creativity can be difficultcan be difficult

ConclusionConclusion

Although there are many theories Although there are many theories regarding the origins and possible regarding the origins and possible evolutionary advantages/disadvantages of evolutionary advantages/disadvantages of schizophrenia, none of them have truly schizophrenia, none of them have truly been provenbeen proven

Up until the 1960’s, studying schizophrenia Up until the 1960’s, studying schizophrenia from an evolutionary perspective was from an evolutionary perspective was unheard of. However, this can only add to unheard of. However, this can only add to our understanding of this severe disorder our understanding of this severe disorder and will hopefully one day benefit those and will hopefully one day benefit those who suffer from schizophrenia who suffer from schizophrenia

The End!The End!