An evolutionary view of depression

From Woodruff Health Sciences Center

A growing body of research is showing that one of the causes of depression may be inflammation, says Andrew Miller, professor of psychiatry and behavioral sciences at Emory. Whenever the body is attacked by a pathogen, the immune system becomes activated. That causes inflammation, a process that releases protein molecules known as cytokines.

“These cytokines can actually get into the brain and start to interact with all the things that we know are important to the development of depression,” Miller says.

Depression is such a common human affliction that it seems almost hard-wired into our brains. Miller and colleagues have proposed that perhaps depression is an evolutionary byproduct of our ability to fight infection. You can read their paper in Molecular Psychiatry.



The reason depression is staying in the gene pool at such a high rate may be that depression is helping us deal with the microbial world, Miller says. “It’s helping us deal with pathogens, as opposed to dealing with other people.”

The researchers looked at genes that are associated with depression one by one, and found that almost every single one of those genes was related to the ability to fight infections.

The behaviors associated with depression, social withdrawal and loss of interest in the external world, help conserve the energy needed to fight infection and heal a wound, Miller says.

Stress can lead to inflammation and ultimately to depression. In acute cases, stress can be a beneficial response, since it ramps up the immune system to help deal with a wound or infection. Chronic stress, however, causes a constant release of cytokines that get into the brain and may cause chronic depression, Miller says.

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