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The Discovery of Depression as an Adaptive Instrument

Michelle hopes to spread awareness of stigmatized health topics by presenting relevant medical findings in her short articles.

In 1873, Charles Darwin, famed for his theory of evolution by natural selection, propounded a revolutionary idea that modern human emotional expressions have evolved from those of human ancestors. Darwin, unknowingly at the time, lay the very groundworks for evolutionary psychology.

Evolutionary psychology adopts Darwin’s evolutionary biology to conclude that the internal mechanisms that humans possess today are adaptations, ones that had been especially crucial to the fitness of early Homo sapiens. Indeed, it is true that the environment of hunter-gatherer societies differs significantly from the 21st century environment; however, it is crucial to acknowledge that although the physical landscape may have changed, the underlying psychological human mechanisms remain present today.

Depression as an Adaptive Mechanism

Recently, scientists have begun to see depression as yet another adaptive quality that has evolved from the continuous need to analyze and respond to complex problems.

A Pleistocene Social Dilemma

The Pleistocene epoch 11,700 years ago saw great land mammals and the expansion and evolution of Homo sapiens

The Pleistocene epoch 11,700 years ago saw great land mammals and the expansion and evolution of Homo sapiens

Even in as seemingly simple societies like those of the small hunter-gatherer bands were complex social dilemmas including conflicting self and group interests. Individuals needed to analyze multiple tactics by which to approach a situation, hoping that the outcome would not endanger the individual’s ultimate fitness within the larger group. This social struggle was often faced by pregnant women, who not only required greater protection from others around them, but also tended to leave their natal groups, forcing them to then seek resources and aid from people they were not genetically related to. These women, facing difficult odds, had to find a way to ensure friendly social relationships with their new group without contributing to any social stress (group interest), while still receiving the crucial medical attention they needed for childbirth (self interest) (Andrews and Thomson, 2009). As a result, those who were able to dissect a complex situation and find an apt solution to ensure cooperative relations and protection were consequently better equipped to survive. Hence, in passing down genetic data to offspring, subsequent generations retained this psychological ability to decipher analytically-difficult issues, seen now in the adaptation of depression.

A Modern Social Dilemma: Prisoner's Dilemma Simulation

To test the hypothesis that depression is, in fact, an adaptive feature of the human body in response to adverse social dilemmas, researchers generated a Prisoner’s Dilemma-inspired simulation. In this study, subjects were placed in pairs and each subject was given the choice to either defect or cooperate.

However, unlike the original Prisoner’s Dilemma game, the subjects’ decisions would not be made simultaneously; instead, one subject (in a low power position) would choose to defect or cooperate before the other, allowing the other subject an advantageous position (high power position) in knowing, in advance, the action of the first subject. Especially pertinent to the study’s conclusion were the test results of two groups: a non-depressed subject paired with a subclinically depressed subject and a non-depressed subject paired with another non-depressed subject. Results indicated that while non-depressed individuals in the higher power situation scored the highest (160.9 points) when paired with a depressed individual, the same non-depressed group scored the lowest when in the low power position (-38.6 points). On the other hand, depressed subjects scored relatively high in both the high and low positions (55.0 points and 139.7 points, respectively) (Hokanson, et al., 1980).

Overall, the depressed subjects were more successful in this simulation than non-depressed subjects. Researchers explained the score difference by acknowledging the tendency of non-depressed subjects to choose to cooperate in both the high power and low power position. Contrarily, the results from depressed subjects indicated varied frequencies of cooperating and defecting, depending on the position they held. Researchers inferred that the depressed analyze social dilemmas differently than the non-depressed, for they weigh the risks of either cooperating or defecting before acting, often exaggerating the costs of their actions (Andrews and Thomson, 2009).

The study thus affirmed that the depressed experience greater rumination of their problems. Scientists then hypothesized that depression itself effects many of the same thought processes and physiological responses required to dedicate one’s full attention on a specific subject (or simply ruminate) as were pertinent to survival in the Pleistocene epoch.

Depression's Effect on Increased Activity in the VLPFC

Location of the VLPFC in the human brain

Location of the VLPFC in the human brain

In general, humans possess a memory system that briefly stores information for comprehension or reasoning. Thus, when humans encounter a problem that requires analysis to produce a solution, they tap into their working memory (WM). However, WM activity is easily disrupted by external distractions that displace the present relevant information, which can draw the individual’s attention away from the initial issue. Therefore, more strenuous WM tasks necessitate greater attentional control to avoid bombardments of extraneous information. Thus, depressed individuals who are confronted by a complex problem experience an increase in functional connectivity between the left ventrolateral prefrontal cortex (VLPFC) and surrounding areas in the brain (Lehrer, 2010). This increase in activity includes a rapid firing of neurons in the VLPFC that helps to reduce any disruption of rumination, which would in turn allow them greater attentional control and focus on the very problem that stimulated their depressed behaviors.

Abnormal neural connectivity in depressed subjects

Abnormal neural connectivity in depressed subjects

In conclusion, many of the modern human functions have ultimately derived from the Pleistocene era, when the very features humans liberally enjoy today were significantly crucial to the fitness of Homo sapiens. Regardless of how drastically different the environment may have been 100,000 years ago, environmental psychologists in the 21st century affirmatively espouse the continuities in human psychological processes, including depression. Recently, various studies have been completed that support the analytical rumination hypothesis, shedding light on how certain physiological responses are triggered when an individual is confronted with a complex social dilemma. Future research may reveal any additional adaptive benefits from this once misconceived mental disorder, ultimately enhancing the human understanding of the long-standing mystery of depression.

References

Andrews, Paul W., and J. Anderson Thomson. “The Bright Side of Being Blue: Depression as an Adaptation for Analyzing Complex Problems.” National Center for Biotechnology Information, U.S. National Library of Medicine, July 2009, www.ncbi.nlm.nih.gov/pmc/articles/PMC2734449/.

Hokanson, J E, et al. “Interpersonal Behavior of Depressive Individuals in a Mixed-Motive Game.” National Center for Biotechnology Information, U.S. National Library of Medicine, June 1980, www.ncbi.nlm.nih.gov/pubmed/7410699/.

Lehrer, Jonah. “Depression's Upside.” The New York Times, The New York Times, 25 Feb. 2010, www.nytimes.com/2010/02/28/magazine/28depression-t.html.

© 2018 Michelle Tram