Depressive personality and depressive illness are examined from an evolutionary adaptationist standpoint. It is postulated that the depressive state evolved in relation to social competition, as an unconscious, involuntary losing strategy, enabling the individual to accept defeat in ritual agonistic encounters and to accommodate to what would otherwise be unacceptably low social rank.

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We trace the development of ideas about the relation of mood to social rank and territory. We suggest that elevated mood enabled a person to rise in rank and cope with the increased activities and responsibilities of a leadership role, while depressed mood enabled a person to accept low rank and to forego the rewards associated with high rank. This led to the concept of a trio of agonist/investor strategy sets, each consisting of escalating and de-escalating strategies, one set at each of the three levels of the triune forebrain. Depressed mood can be seen as a de-escalating (appeasement) strategy at the lowest (reptilian) level; this should facilitate de-escalation at the highest (rational) level, but sometimes this rational level de-escalation is blocked (e.g., by stubbornness, courage, pride or ambition) and then clinical depression may ensue. These evolved psychobiological mechanisms survived the partial transition from agonistic to prestige competition. We discuss difficulties which have arisen with our ideas, and their implications for clinical work and research.