View Full Version : The Evolutionary Advantage of Depression

Scarlet Ibis
10-14-2012, 02:18 AM
See the study here: http://ajph.aphapublications.org/doi/pdf/10.2105/AJPH.79.10.1396



...As we learn more about the human genome, scientists are finding evidence that while depression seems incredibly maladaptive, it was actually adaptive (helpful) to our ancestors.

Recently Dr. Andrew Miller and Dr. Charles Raison, physicians at Emory University and the University of Arizona, respectively, authored a paper "The evolutionary significance of depression in pathogen host defense" in which they proposed that some of the alleles (forms of genes) that increase one's risk for depression also enhance immune responses to infections.

Commenting on their hypothesis, Dr. Miller noted, "Most of the genetic variations that have been linked to depression turn out to affect the function of the immune system." Dr. Charles Raison of the University of Arizona added, "The basic idea 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."

....Today, certain mutated versions of a gene called "NPY" are associated with increased inflammation (an immune process helpful in fighting off infections). Mutated NPY genes likely allowed our ancestors to better fight off infections (especially in childhood), and individuals with the mutated NPY gene were more likely to pass along the mutated NPY gene to offspring.

Interestingly, researchers at the University of Michigan's Molecular and Behavioral Neuroscience Institute discovered that individuals with major depressive disorder were more likely to have the mutated NPY gene. The normal NPY gene codes for higher levels of a neurotransmitter known as Neuropeptide Y, which appears to help ward off depression by increasing one's tolerance of stress. So the same mutated NPY gene that likely protected our ancestors against pathogens also increases our chance of developing depression.

Drs. Miller and Raison believe that acute (or severe but short-term) stress can not only lead to depression, but also jump-start the immune system. The physicians note that in the environments in which our ancestors lived, acute stress was often associated with the threat of physical harm or physical wounds. And unlike today, wounds readily led to infection and death. Therefore, Drs. Miller and Raison believe that evolution favored individuals whose immune systems operated under a "smoke-detector principle."

Although smoke detectors often react to false alarms (for me, burnt toast), if you removed the detector's battery and a real fire occurred, the consequences could be severe. Similarly, immune responses to acute stress are typically not necessary -- not every stressful situation results in a wound and infection. However, if our ancestors became wounded even a single time and didn't experience a piqued immune response, they might die from an infection.

It turns out that depression may not be a mere trade-off for a vigorous immune response. Dr. Miller suggests that depressive symptoms like social withdrawal, lack of energy, and a loss of interest in once enjoyable activities were actually advantageous to our ancestors. For example, a loss of energy might ensure that the body can leverage all of its energy to fight an infection. Also, social withdrawal minimizes the likelihood of being exposed to additional infectious agents. In this way, Drs. Miller and Raison note that "depressive symptoms are inextricably intertwined with -- and generated by -- physiological responses to infection that, on average, have been selected as a result of reducing infectious mortality across mammalian evolution." ......

Read the full article here: http://www.theatlantic.com/health/archive/2012/10/the-evolutionary-advantage-of-depression/263124/

10-14-2012, 05:25 AM
Yeah, well, I've been depressed, paranoid and apathetic just about as long as I can remember. I'm used to it. It is my normal state. So what!? I don't have the money for s shrink, and wouldn't waste it on one if I had it. Cheers!