Mental illness: part of our evolution?
Evolution allows species to become increasingly well-adapted to their environments over time. The advantageous traits, and the gene variants that underlie them, become more common, while harmful characteristics become less frequent.
When we consider mental illness, or any disorder for that matter, this view of evolution becomes confusing. Surely schizophrenia and chronic anxiety are not beneficial traits. How can this be?
Recent research in this area was summarised in a Nature News article. Many traits, and the genes that underlie them, are not harmful enough to be actively selected against. If they are located near a beneficial gene variant on a chromosome, they may hitch a transgenerational ride. One study of individuals across Europe, for example, suggests that those living in colder regions had a higher risk of schizophrenia than people in warmer regions. The authors of the study concluded that, perhaps, the genes that promote survival in cold weather are located near genes that predispose people to develop schizophrenia.
Some advantageous traits may have even increased our risk for mental illness. Our ancestors may have benefited from a strong immune system. Unfortunately, many psychiatric disorders, such as depression, may result from a hyperactive immune system that is always switched on and exacerbated by modern-day stress and poor diet.
It will be some time before scientists fully understand how evolution has played a role in mental illness. For now, it is an exciting new lens through which we can look at mental health and, hopefully, understand it better.