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Here is something somewhat counter our way of thinking.  An article is arguing that depression can actually be beneficial in fighting off disease.  Read below to see this surprising theory.

The fact that depression exists – not only exists, but plagues such a vast number of people – has presented a major mystery. Anyone who has suffered from major depression can tell you that oftentimes it makes no sense: there can be little connection between life events and the severity of the illness, which can virtually destroy one’s ability to function in everyday life. Researchers, too, have long puzzled over a good explanation for why depression came to be at all. Now, a smart new theory may offer some insight.

Most behaviors and states we experience make some sort of sense in an evolutionary light. For example, although anxiety can be incredibly counterproductive, even damaging, as many experience it today, we basically know why it evolved: The stress response helped us (and still helps us) get revved up for a fight or flight from adversaries. Generalized anxiety is an unfortunate fallout from the stress response being chronically “on,” which is what a lot of people experience these days.

But depression’s evolutionary “value” has been much less clear. In fact, the authors of an intriguing new paper point out that even more bizarre is the fact that there are genes that put people at greater risk for depression. Not only have these genes stuck around throughout history, but they actually seem to have become more prevalent in the population. If depression was a truly maladaptive state, you’d think these genes – and depression itself – would have been weeded out by now. Since they haven’t, and since depression still exists in spades, there must be some purpose to depression and the genes that put one at risk for it.

The answer, the authors argue, is that the genes that are linked to depression are also involved in our immune system function. Fighting off infection was a frequent pastime of our ancestors, and a leading cause of death. People who had the genes for depression, the argument goes, were better infection-fighters because depression-like symptoms are conducive to infection-fighting.

“Most of the genetic variations that have been linked to depression turn out to affect the function of the immune system,” author Andrew Miller said in a news release. “This led us to rethink why depression seems to stay embedded in the genome.”

The compounds that get released in the immune response – cytokines – appear to naturally trigger behaviors that are similar to depression’s symptoms: low mood, anhedonia (the inability to find pleasure in previously pleasurable activities), psychomotor retardation (slowing of motor and thought processes), fatigue, social avoidance, and anorexia (weight loss). These symptoms are thought to occur because the body is rerouting its valuable energy reserves to the greater good: Infection-fighting. Laying low, mentally and physically, translates into feeling low, but would theoretically help resources be poured into immune system activity.

“The basic idea,” said author Charles Raison, “is that depression and the genes that promote it were very adaptive for helping people—especially young children—not die of infection in the ancestral environment, even if those same behaviors are not helpful in our relationships with other people.” So while depression may be maladaptive when it comes to mood and social interactions, the symptoms could be quite adaptive when it comes to keeping a person alive while fighting infection.

Further support for the depression-immune system connection comes from reports from people who have autoimmune disorders, like rheumatoid arthritis and ulcerative colitis. If you block cytokines, the inflammatory molecules, in people with autoimmune disorders, says Miller, their mood is actually elevated.

The theory also helps explain why stress can trigger depressive episodes. It may be the body’s effort to amp up the immune response in preparation for infection.

So, maybe depression has some “purpose” to it after all. This theory may be the best we have so far to explain the pervasiveness of depression. Still, considering the destructive effects of depression, it’s not exactly evolution’s best move. Since it’s probably not too likely to be weeded out in the future, the best we can do is to find the most effective method of coping with its existence now. What this may be, of course, is a whole other story.

What do you think about this theory of the evolution of depression?

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