Depression Under the Light of Evolution: Two Evolutionary Hypotheses that Make Sense of Non-Disordered Depressed Mood

Herrick Hospital-Psychiatry Grand Rounds:  Presentation by Julio Ozores, MD, UC Berkeley and The Wright Institute

A New View of How to Think About Depression
 
In assessing a patient who complains of depression, the biological, psychic and social components will, ideally all be considered by the treating professional.  Dr. Ozores adds another possible component, that of evolution.  There may be a reason that we have the capacity to be depressed at times; according to evolutionary theory, it is proposed that there may be times when depression is adaptive.

There is some history for this theory.  Darwin himself wrote about behavior and psychology, albeit, briefly.  Following were some offers on this subject by William James, James Baldwin, Freud and Jung.  Then came the period of reductionism when psychology was all about behaviorism.  Biology came back into the picture when it was recognized that human readiness to learn certain things exists in ways that are different from animals.  There is a Periodic Table for Psychology by Tinbergen depicting this development of the field.  Recent work has brought to light the question of why the symptom is present; when the body is injured and there is pain, behavior is organized around dealing with that.  Perhaps the same is true of depression.  Some depression may be adaptive, a way of dealing with certain situations.

Dr. Ozores did a critical evaluation of two Evolutionary Hypotheses of Depressed Mood.  Depression is prevalent.  Varying degrees of depression are universal.  The two theories are The Social Competition Hypothesis and The Social Risk Hypothesis.  The first is outlined in a book called The Maladapted Mind.  The first was explained in how all animals fight.  There is a loser who has to stop challenging, lower aspirations, and signal that the fight is over.  This generates a sense of incapacity, subordination and entrapment.  Defeat leads to depression.  Low rank=decreased serotonin.  Thus, according to Dr. Ozores' delineation of this theory, this creates social symmetry.
 In The Social Risk Hypothesis  (written about in a paper by Nicholas Allen and Paul B T Badcock), humans fight but also intensively cooperate.  We all belong to groups so social standing is crucial but, precarious; there is the threat of exclusion and ostracism.  Humans have mechanisms to monitor social standing.  Looking for signs of affiliation may lead to a shift to a risk aversive state.
He defines Non-Disordered Depressed (meaning, this can occur for periods of time as a part of the normal range of human states of mind) mood as:   Anhedonia, low motivation, loss of energy, low self-esteem, sense of incapacity, self-deprecation, negative cognitive biases, hypersensitivity, social withdrawal, sadness.

Convergence:  The study of the stress response, evolutionary psychology, ethology, and clinical psychiatry are converging on a model of clinical depression that understands it as a dysfunction of mechanisms that regulate social behavior.  The depression is causally linked to current environmental stressors in the person's life, and the stress must be specific.  It must be able to be shown how it developed to help cope with the precipitating stressors.

Consilience:  The sciences may meld, Dr. Ozores predicts, and be found to have foundations in each other.  There is an emerging consilience between psychiatry and the biology of behavior with evolutionary thinking.