Schizophrenia: An Evolutionary Perspective By: Tanya Kraus Schizophrenia a psychotic disorder characterized by major disturbances in thought, emotion, and behaviour – disordered thinking in which ideas are not logically related, faulty perception and attention, flat or inappropriate affect, and bizarre disturbances in motor activity. Patients with schizophrenia often withdraw from people and reality into a fantasy life of delusions and hallucinations. Positive/Negative Symptoms Positive symptoms: Involves behaviour that is not normally present in most people. (E.g. distortions, disorganized speech, hallucinations, or delusions.) Negative symptoms: Involves behavioural deficits that are not present in most people. (E.g. avolition, alogia, anhedonia, flat affect, and asociality.) Other Symptoms Many patients experience the following as well as positive and negative symptoms. Catatonia: Defined by several motor abnormalities, which can include catatonic immobility or waxy flexibility Inappropriate Affect: Emotional responses that are out of context Here’s Where the Evolution Part Becomes Relevant… Unusual behaviours that strongly resemble schizophrenia have dated back to Mesopotamia Universally, the prevalence rate of schizophrenia is about 1%, which exceeds common mutation rates There is a strong genetic component (E.g. twin and adoption studies) Conditions such as schizophrenia have a long history and a strong genetic base, meaning evolutionary explanations must be acknowledged Evolution Perspectives Evolutionary perspectives can be divided into two groups: a) Theories that assume schizophrenia is a disadvantageous by-product of human brain evolution b) Theories that consider schizophrenia to have an evolutionary advantage Schizophrenia: Disadvantageous ByProduct of Human Brain Evolution Theory #1: Farley’s argument that schizophrenia could be an extreme variant of normal social behaviour Flaw: This theory fails to explain why schizophrenia is comprised of both negative and positive symptoms Disadvantages, Cont. Theory #2: Randall’s novel neural pathways model…”biological trial and error of connection would produce a range of behavioural variants, including schizophrenia.” Flaw: Denies the specific symptoms that occur in any given disorder, as well as the maintenance of pathology Disadvantages, Cont. Theory #3: Saugstad’s pathophysiological model, which connects many frontal lobe disorders (E.g. schizophrenia, infantile autism), to delayed cerebral maturation. Again, schizophrenia is viewed simply as an outlier within the normal bounds of variation Flaw: It would be atypical for nature to produce such large numbers of distinct phenotypes with reduced fecundity (Ability to produce many children) Disadvantages, Cont. Theory #4: Yeo and the developmental instability model of schizophrenia Flaw: While being a very intriguing theory, it lacks any empirical evidence at this point in time. It should be considered speculatively Schizophrenia as an Evolutionary Advantage Schizophrenia paradox: “The discrepancy between high prevalence rate and reduced fecundity” This doesn’t seem very adaptive, does it? There must have been some evolutionary advantage to having schizophrenia… Advantageous Theories Theory #1: Huxley, Mayr, Osmond, and Hoffer published the first model linking schizophrenia to evolutionary concepts. (1964) Speculated that reduced fecundity was compensated by higher resistance to allergens, shock, and infection Flaw: No substantial evidence supporting this theory Advantageous, Cont. Theory #2: Kellet’s model suggesting that certain characteristics found in schizophrenia may have helped man’s territorial instincts Flaw: This theory addresses only a small component of schizophrenia, providing no evolutionary explanation for psychotic symptoms Advantageous, Cont. Theory #3: The schizophrenia gene could possibly benefit individuals who carry it but do not have the disorder Karlsson studied a population of schizophrenics in Iceland and discovered that first-degree relatives were twice as likely to be members of creative professions than the general population Flaw: Providing an accurate association between psychiatric conditions and creativity can be difficult Conclusion Although there are many theories regarding the origins and possible evolutionary advantages/disadvantages of schizophrenia, none of them have truly been proven Up until the 1960’s, studying schizophrenia from an evolutionary perspective was unheard of. However, this can only add to our understanding of this severe disorder and will hopefully one day benefit those who suffer from schizophrenia The End!