The evolution of mental illness has always interested me, after our discussion in class about Schizophrenia, I became interested in the evolution of depression. Unlike Schizophrenia, depression is a common mental disorder, it is estimated to affect 121 million people all over the world and the number of people who have been diagnosed is increasing at a 20% rate per year. This phenomenon puzzles evolutionary biologists and psychiatrists because the alleles that are responsible for depression should be selected against over time according to the four postulates of evolution. This paradox is examined in this NYTimes article.
The proximate cause of depression is rumination, which means that people fixate on their flaws and problems, and extending their negative moods, rumination decrease a person’s functionality in daily life and it is considered useless, waste of mental energy. Rumination is associated with ventrolateral prefrontal cortex (VLPFC), which is located a few inches behind the forehead. Interestingly, VLPFC is also responsible for intense focus which is necessary to produce meaningful work. Therefore, it is hypothesized that depression has the benefit to allow the individual to have an increased brain activity that normal people cannot achieve. In another word, depression is an extreme end at the spectrum of ordinary thought process, and the inability to engage in pleasant activities help the depressed person focus better on their work
The question is, does depression and sadness indeed make people more productive for being more attentive? Psychiatrists and researchers has argued that many patients who have suffered from depression have a hard time performing daily functions such as bathe or eat, not to mention work and solve problems. These counter arguments suggest that the benefit theory of depression is a stretch.
Another school of psychiatrists suggest that depression could be a warning sign like chronic pain. Only by seeing a therapists and walk through the rumination process, can patients who suffer from depression find out the fundamental cause of depression.
This leads to the conclusion from the author which I think perfectly describes the relationship between emotions and consciousness, “ This is the paradox of evolution: even if our pain is useful, the urge to escape from the pain remains the most powerful instinct of all.”
I think this post was incredibly interesting. I have shadowed psychiatrists over the summer, and those experiences were able to drastically redefine my views of depression and its stigma in modern society. I think these hypotheses are very interesting, particularly the possibility that depression may allow an individual to attain increased focus as associated with the VLPC. I think this theory may have credibility, and it may be interesting to see, as we have seen in other cases that a mild form (rather than a debilitating form, or no depression) may increase human focus to a slightly higher amount without introducing too many negative effects of depression. Though I would question how improved focus increases fitness for producing offspring. This “mild” selective advantage is also a hypothesis prevalent when looking at individuals with Iron Deficiency Anemia and an increased fitness due to decreasing the likelihood of the spread of iron – dependent pathogens. Similar hypothesis are also seen with sickle cell anemia carriers and their subsequent protection from malaria.
From what I have seen in my experience with psychiatrists, depression is highly individualized, specifically a product of that individual’s mind and state as a result of their environment, their past, experiences, etc. Hence; I think how an individual responds to depression (either with increased focus or lack thereof) is highly individualized, and may be tough to find a fixed pattern. In this case, I think evolutionary studies specifically looking at depression must also heavily consider the epidemiology of depression to understand the evolutionary framework behind it.
Very interesting article!