Did Depression Evolve to Help Us?
Some of our daily life revolves around compromise. There's the cost-benefit issue with medication for example, or the decision about whether to pay a little more for something, or those times we agree to do things in order to please someone else. I suspect few people have considered the role of depression as a trade-off, but it's a suggestion put forward by research psychiatrists who wonder whether depression is an evolutionary byproduct of our immune systems.
The purpose of depression is something that has been debated for some time. I briefly explored this a while back when I asked, is depression good for us?
The fact that depression is so common leads to speculation about whether it is hard-wired into our brains. But what could the possible merits be of such a disabling and unrewarding disease process? Andrew Miller, MD and William P. Timmie, professor of psychiatry and behavioral sciences at Emory have suggested the possible role of depression in relation to fighting infection.
The development of the new theory stems in part from observations that depression and inflammation, or over-activity in the immune system, tends to correspond. Even if a person with depression has no infection they tend to have higher levels of inflammation. According to the authors, most genetic variations linked to depression turn out to affect the immune system.
Turning back the clock, the authors speculate that the genes promoting depression would have been helpful for our ancient ancestors, especially children. Everyone knows that infection was a significant cause of infant mortality. In this context the bringing together of depression and infection may have been nature's way of trying to adapt. In order to fight infection fever, fatigue, social and physical inactivity could be viewed as adaptive behaviors in the light of needing to contain infection.
Stress has always been viewed as a risk factor for depression. Stress is also known to activate the immune system. In ancient times this would be a necessary survival process. The authors suggest that the link between stress and depression can be considered a byproduct of the process that activates the immune system in anticipation of some physical injury. Likewise, activation of the immune system is associated with mood disorders and disruption in sleep patterns. The authors speculate this may come from our ancestors' need to stay alert to fend of predators after injury.
Future research for depression may be guided by the idea that certain biomarkers for inflammation might help to predict whether someone will respond to various treatments for depression. This extends work previously undertaken at Emory looking at how reducing inflammation can reduce depression. Also, whether drugs normally used to treat autoimmune diseases, can be effective with treatment-resistant depression.
Emory University (2012, March 1). Depression: An evolutionary byproduct of immune system?. Science Daily. Retrieved March 29, 2012, from http://www.sciencedaily.com/releases/2012/03/120301103756.htm