Finding evolutionary explanations for susceptibility to disease is difficult, and mistakes are inevitable. The most common and worst mistake in evolutionary medicine is the tendency to view disease as an adaptation.
Therefore, it never hurts to remind once again: the diseases themselves have no evolutionary explanation, these are not adaptations formed by natural selection. Genes or traits associated with a number of diseases provide advantages and disadvantages that influence selection. However, all assumptions about the benefits of diseases themselves, such as schizophrenia, addiction, autism, bipolar disorder, are fundamentally wrong. The question should sound like this: “Why, in the course of natural selection, have formed the traits due to which we have diseases?”
Disease susceptibility requires an evolutionary explanation that takes into account one or another combination of the above factors. Someone strives to look for one single reason, for example, to blame everything only on the modern environment, only on costs or only on restrictions. But, as a rule, this is an ensemble of several reasons at once. So, for example, explaining atherosclerosis from an evolutionary point of view, we take into account both the modern diet, and infections that cause inflammation, and the harm and benefits of immune activation in the arteries. Finally, we must not forget that evolutionary explanations are not an alternative to explanations describing how systems function. We need both.
Without an evolutionary explanation, we will not be able to understand why mental illness exists in principle, where to look for their causes, and in what direction to work on improving the methods of treatment.