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Origins

Late 19th Century and Early 20th Century

Although the term "evolutionary psychiatry" was coined in 1985 by Paul MacLean, this theory originated in the nineteenth century. During this time, Charles Darwin had begun his work on The Expression of the Emotions in Man and Animals in collaboration with British psychiatrist, James Crichton-Browne . The purpose of The Expression was to close the gap between humans and animals by demonstrating that various facial elements (i.e., skeletal, muscular, etc) are involved in generating emotion in both species. For his research, Darwin observed psychiatric patients and their emotional responses. Psychiatric patients served as excellent research subjects as they are often unable to filter their emotions. After collecting data, Darwin would relay his observations to Crichton-Browne to better understand the psychological aspects. While Darwin is known for his theory of natural selection, he explained the origins of emotions in terms of involuntary and habitual actions in The Expression. The idea of emotional adaptation or selection as the underlying cause for mental disorders is a newer concept found in contemporary evolutionary psychiatry. The degeneration theory was another common theme in evolutionary psychiatry at this time. This theory, which was often used to promote white supremacy, viewed mental illness as a result of "bad hereditary" that certain groups or races were predisposed to. Although the degeneration theory was common in early Darwinian psychiatry, it is still unclear if Darwin actually approved of it. However, most evidence suggests he did not.

Also see History of Evolutionary Psychology

Evolutionary psychiatry and schizophrenia

Psychotic disorders are a common field of study for many evolutionary psychiatrists, schizophrenia being one of the most prevalent. This psychiatric condition is believed to have emerged after humans diverged from Neanderthals. Researchers unearthed this timeline upon conducting a genome-wide comparison between people with schizophrenia and Neanderthals. They found that the risk loci present within schizophrenic patients was absent in Neanderthal genes. Ole Andreassen, professor at the University of Oslo in Norway, explains that:

Our findings suggest that schizophrenia vulnerability rose after the divergence of modern humans from Neanderthals, and thus support the hypothesis that schizophrenia is a by-product of the complex evolution of the human brain.

As previously mentioned, evolutionary psychiatrists look to address mental disorders through Darwin's theory of natural selection. New traits arise from genetic mutations which offer advantages to the population that are then passed down through generations. This is known as survival of the fittest. Psychiatrist Godfrey Pearlson illustrates that, "Although most phenotypes are said to be 'selected for' based on adaptive qualities, it is difficult to understand how the genetic basis of schizophrenia could have operated under a similar framework." This assumption has lead evolutionary psychiatrists to form two theories on the origins of schizophrenia: (1) schizophrenia is a disadvantageous byproduct of human brain evolution and (2) schizophrenia is an evolutionary advantage.

Schizophrenia as a disadvantageous byproduct

Phenotypes are observable traits determined by the genotypes, or the total genetic inheritance, of an individual. Interactions between various genotypes result in different phenotypes. Evolutionary psychiatrists believe that the phenotype for schizophrenia is a result of an abnormal variant of the genotype for a different behavior, possibly speech. One common theory is that schizophrenia emerged with language and was therefore a disadvantageous result of the evolution of speech. British psychiatrist, Tim Crow, explains this emergence:

Predisposition toward schizophrenia and other psychotic ailments reflects phenotypic variation associated with the capacity for language. The possible lack of cerebral asymmetry observed in schizophrenia, along with alterations in speech, ties the illness to language.

Crow and other scientists argues that language could have evolved as a consequence of sexual selection. Males compete with one another to mate with a female, and according to Darwin's theory of natural selection, the female will choose the best-fit male. Crow believes brain plasticity increased as sexual-selective pressure increased. This increased plasticity allowed for higher intelligence, and therefore, the emergence of language. However, this theory creates several assumptions that non-evolutionary psychiatrists deem incomplete or contradictory. First, certain scientists are concerned that Crow's theory about language does not touch on the other aspects of the disorder, as it does not offer an explanation for irregular social behaviors like ticks and hallucinations. Secondly, this theory assumes that language evolved quickly or from a singular gene, which goes against the evolutionary theory of punctuated equilibria.

Schizophrenia as an evolutionary advantage

The "schizophrenia paradox" centers around the question of, "Why is schizophrenia still so prevalent?" From an evolutionary viewpoint, natural selection should have abolished the gene for schizophrenia a long time ago. With only seemingly negative consequences, such as low fecundity, schizophrenia does not outwardly appear to benefit the species. This has led evolutionary psychiatrists to believe schizophrenia emerged with accompanying advantageous characteristics. Evolutionary psychiatrists believe that the low fertility rates observed in schizophrenic individuals was compensated for by higher resistance to shock, allergies, and infection (although this idea does not have much empirical basis. This theory about schizophrenia can be compared to sickle cell anemia's coexisting favorable and unfavorable evolutionary effects. While the homozygotic genotype of sickle cell anemia can result in pain and blood clots, it provides immunity against malaria. Evolutionary psychiatrists believe that the homozygotic genotype of schizophrenia can also provide benefits.