Evolutionary aspects of schizophrenia

Disorders of the mental life have accompanied the species Homo sapiens since the beginning of its existence. One of the most serious is schizophrenia. Its presence in all cultures, with similar frequency, indicates that this disease probably appeared before the formation of the oldest genetically isolated populations. Schizophrenia is also associated with the phenomenon of the so-called "evolutionary paradox". It concerns a situation in which genetic variants predisposing to the disease persist in the population despite the deterioration of the fitness of people affected by the disease, early onset of the disease, higher mortality and, consequently, reduced reproductive capacity. This seemingly contradicts the classical Darwinian theory of evolution, according to which natural selection promotes genetic variants that give an advantage in the above areas. In this article, we will try to present theories and hypotheses, often complementary, sometimes contradictory, that try to explain the causes of this puzzle. We will look at the evidence that allows us to treat schizophrenia as an adaptive advantage, but also that which considers it an unfavorable, although inevitable, product of brain evolution. We will point to potential genetic, metabolic, and social factors that may be involved in perpetuating the "evolutionary paradox" of schizophrenia mentioned above.