The last few years have seen extensive efforts to catalogue human genetic variation and correlate it with phenotypic behavioral differences. Central to the field of psychiatric molecular genetics is the search for “vulnerability genes”. The general medical model explains that there are genetic and environmental risks and protective factors in the aetiology of any complex disease. The main idea supported by this model is the existence of good and bad polymorphisms.

According to the evolution theory, the persistence of any genetic trait in the population depends on its potential to increase fitness for individual survival and reproduction. Therefore, genetic variants associated with vulnerability to mental illness should be under strong negative selection pressure and be eliminated from the genetic pool through natural selection. Still, mental disorders remain common. The question of how heritable yet harmful traits associated with vulnerability to mental illness survived the fitness-maximizing process of evolution by natural selection is a major puzzle that psychiatric genetics is faced with.

We present some examples of our own empirical studies in depression and schizophrenia about this issue.