In today’s Academic Minute, Dr. Andrew Miller of Emory University explains why natural selection has not eliminated genetically predisposed depression.
Dr. Andrew Miller is William P. Timmie Professor of Psychiatry and Behavioral Sciences at Emory University and Director of Psychiatric Oncology at the Winship Cancer Institute. His work focuses on the impact of the activated innate immune system on behavior and health. Dr. Miller has published over 120 manuscripts in scholarly journals and has edited a book entitled Depressive Disorders and Immunity.
Dr. Andrew Miller, Emory University – Evolutionary Persistence of Depression
There has been a longstanding debate as to why depression is so prevalent in our society, affecting up to 10% of adults. Depression has devastating effects on our relationships with other people and our ability to function in society. So why do the genes for depression remain in the gene pool when there appears to be no evolutionary advantage? Recent work by Dr. Charles Raison and me may provide some answers.
We and other scientists have long suspected that depression is associated with an aggressive immune response. This aggressive immune response leads to the release of infection-fighting molecules called cytokines, which can enter the brain and cause social withdrawal and reduced activity, primary symptoms of depression. Interestingly, when the genes most robustly associated with depression were examined, almost every one of them was associated with the immune system or the ability to fight infection.
These findings suggest that rather than being designed to deal with the social world, the genes for depression may be most suited for dealing with the microbial world, including pathogens such as bacteria and viruses. Being better at fighting pathogens would ensure survival especially in ancestral times when pathogen loads were high. So why the link with depression?
It turns out that social withdrawal and reduced activity help the body eliminate pathogens by shunting energy resources to fight infection. Thus symptoms of depression are part of an integrated behavioral and immune response to infection, and the genes for depression are so prevalent because they were designed to deal with pathogens not people.