Many plausible links have been drawn between genetics and various mental disorders (for example, schizophrenia is frequently linked to the NOTCH4 gene; bipolar disorder is frequently linked to the NRG1 gene). However, a conversation with an acquaintance regarding the social stigma they experienced after being diagnosed with a mental disorder got me thinking about the origins of such disorders. Surely such traits would be extremely maladaptive in an increasingly social world.

     Of course, there is some debate as to whether there are causal mechanisms for genetic links to mental disorders, as well as whether the diagnosis of mental illness is valid and reliable. However, for the sake of brevity, let’s assume that this is the case.

     Whilst some cases have been known to simply be the product of de novo mutations (spontaneous mutations not inherited from either parent), this does not support other evidence that indicates a significant level of heritability amongst mental disorders. So, what else could explain the presence of such genes today?

     The explanation could, of course, be far more simple – the modern Homo sapien could have simply been removed from the selective pressures that would have caused mental disorders to be selected against in the first place. Similarly, many such disorders do not present themselves until the individual’s reproductive span has already begun. However, there are some slightly more radical theories appearing today.

     Dr. Peter McGuffin, when asked about the evolution of mental disorders, made an analogy between sickle cell disease and mental disorders. This is because, although sickle cell disease is selected against, it does give its sufferers some resistance to malaria, which increases its frequency in a population. Dr. McGuffin argues that the same could be happening with mental disorders, and found a higher fertility rate amongst the unaffected relatives of depression sufferers.

     Although mental disorders are usually polygenic and not explained by the simple inheritance of a single trait, it’ll be interesting to see what, if anything at all, this research is eventually able to tell us about the way in which such disorders have evolved.