Depression: Evolutionary byproduct of the ability to fight infection?

Depression affects 1 in 10 persons in the USA.  For several years, researchers have seen links between depression and inflammation, or over-activation of the immune system. People with depression tend to have higher levels of inflammation, even if they’re not fighting an infection.

In evolutionary past, infection was the main threat to the ability of an individual to pass on their genes to a new generation. Fever, fatigue/inactivity, social avoidance and anorexia can all be seen as adaptive behaviors in light of the need to contain infection, the researchers suggest.

The theory provides a new explanation for why stress is a risk factor for depression. The link between stress and depression can be seen as the byproduct of a process that preactivates the immune system in anticipation of a wound.


In a separate piece of research at Emory University School of Medicine, the immune system has been identified as a mechanism by which stress is translated into raised blood pressure.