Sunday, February 20, 2011

Evolution of Depression

Depression for many is more than a label, more than an inconvenience, more than just a certain percentage of the population--it’s a debilitating ailment that can seriously reduce the quality of their life. For reasons of compassion and not just dispassionate science, can evolutionary psychology help to shed any light on the nature of the problem and therefor the nature of a possible relief of depression?

First, let’s consider what an emotion is. Why do we feel anything let alone sadness or depression? Why be happy? Why be angry? Well, emotions are action incentivizers. They help us decide to do something. They are cognitive shorthand. Instead of having to think through a response to a stimulus; you feel and immediately act. To use an hackneyed example, say a cougar is crouching behind an acaia tree. Instead of programming a brain to do complicated risk analyses or cost/benefits assessment evolution has shorthanded that into a “o-shit” terror emotion. Emotions speed up thought.

Great. Now, more specifically, why do we feel sadness or depression? That’s a very complex question, but generally speaking the answer is going to lie within several categories:

Memory Tagging: Perhaps you’ve heard the truism that stupidity can be defined as doing the same thing repeatedly and expecting different results. Negative, ‘sad’ tags on memories can help us avoid the same mistakes twice.

Decision Making: This is much the same as the above, but is mentioned to emphasize that we don’t have to have gone through something to know that doing it would cause emotional pain. We want to avoid emotional duress both in the future and present and sadness helps us do that.

Social Cohesion: If a member of the group is lost then a new social structure, hierarchy, chain of command, reciprocal altruism network, etc. must be set up to maximize the potential of the group staying unified. A void has been created and sadness and mourning can cause the group to come together to reform and heal the wound inflicted on the group.

Were it only that easy. That’s sadness, but I’m defining depression as a subcategory of sadness as a debilitating, isolating, self-destructive emotion far beyond the normal, healthy emotion. How has evolution brought us to that point?

Conservation of Energy/Pathogen isolation: Depression can cause 
Psycho-motor retardation is essentially feeling is emotionally tired that you can't motivate yourself to even do simple tasks, which results in the conservation of energy as well as isolation from pathogens.  

Saving Face: Separating one’s self from the group during a period of depression might have served a function of preventing the loss of face and helped maintain social status upon reemersion and thereby increased reproductive success.

Virtual Stress Simulation/Survival of the Eeyors:  How does an animal learn what is dangerous and what isn't?  Well, it can be taught from relatives, trial and error, it can watch others be eaten or, more importantly for this discussion, it can cognitively simulate and predict.  It may have very well been a selective advantage to speculate every conceivable way things could go wrong and then to virtually and emotionally feel the threat of it so as to avoid the danger.  For instance, if you assume the winter will be frigid and bleak then you might survive better than ole Dr. Pangloss.  It's an emotionally awful way to live, but at least you survive.  Not only does it give you the incentive to avoid a stimulus to avoid the emotional pain that you've simulated before, but it also gives you a chance to run the simulation and problem solve valuable solutions.  You're priming the brain to deal with obstacles.

Brain Priming: It's been shown that as the number of traumatic events increase in a person's life, so does the risk of depression and cognitive unrest.  You've heard the phrase, "Use it or lose it."  Well, the opposite, of course, is also true.  If you use the stress centers of your brain often and for extended periods of times then they become primed and ready to release more stress hormone.  You can imagine that this once had a survival advantage for keeping animals constantly on edge to be ready for a threat.  Now it just ruins lives.

Rumination: Depression sufferers have heightened blood flow to an area known as the left ventrolateral prefrontal cortex as well as increased amounts of serotonin receptors like the 5-HT2A receptor. Both have been shown to serve a function in problem solving. There have even been
numerous studies that have shown that people put in situations that alter their moods toward melancholy score better on problem solving tests, habitually depressed people are more successful professionally and are better problems solvers and people asked in a study to problem solve are more depressed afterwards. Even the behavior of isolation aids in problem solving by reducing distractions.

Combination of Multiple Adaptations/Spandrel: It’s conceivable that depression isn’t one thing, but a multiplicity of mental agencies happening in conjunction. For instance, perhaps depression is the result of a heightened state of self-awareness (which could have selective advantage for obeying social mores and thereby gaining more mates) combined with a focused consciousness (which could have been an advantage for constantly being aware of a child’s safety/needs, problem solving, etc.). These two healthy mental functions aligned could produce a person fixated on self criticism and self condemnation.

Over-Amplified Adaptation/Too Much of a Good Thing: This is classic Darwinism. Within any population there will be variation in a typically bell curve fashion of the manifestation of healthy adaptations, some of which will have too much of a good thing.

Mutation: We shouldn’t ignore the fact that perhaps much of depression is just an unfortunate roll of the mutational dice producing a certain set of brain related genes (like a down regulation of serotonin, etc.). There are undoubtedly times where depression is clearly due to a malfunction such as after brain injuries/strokes.

Emotional Muting: Oddly enough, it’s possible that depression is actually a muting of emotions rather than an profusion of them. Those that are familiar with deep depression are familiar with the bland, dead, muting effect it can have on emotions (sometimes accompanied by manic swings to the opposite end of the emotional spectrum). Is it possible that this emotional flat lining or anhedonia is a form of emotional self protection to prevent something? Perhaps not, but its food for thought.

Defeat Signalling: Communication is paramount in communal animals like us. Just look at our faces. Our lips, eyebrows, facial muscles, larynx placement, Brocca/Wernicke’s area of the brain, are all adaptations that testify to the massive need we have to communicate as humans. Emotional also serve this function and it could be that sadness served as a communication display to end spats.

Submissive Placement: Groups that don’t have hierarchy have difficulty staying together. Groups that don’t stay together often don’t survive. Just as there are adaptations that promote leadership qualities and aspirations there are adaptations that are valuable in promoting omega positions in the group. Depression might aid in cognitively forming omega individuals which are valuable in social cohesion as the counterpoint to alphas.

Alien Environment: Let’s not forget what we’re really evolved for--small tight nit tribes on the African savanna. It doesn’t take a rocket surgeon :) to realize that much of the organization in our society might not be emotionally healthy for us. The double whammy of stress and isolation can be crippling for many of us setting us on a track of spiraling depression. It should be noted, however, that remote
hunter gatherer societies are equally rife with depression as well, though.

Works Sighted [sic]:

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