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The Social Navigation Hypothesis of Unipolar Depression:

An Evolutionary Adaptationist Analysis of Low Mood,

with Significant Practical Implications for Successful Long-Term Treatment.

What if depression, even major clinical depression, is an important evolutionary adaptation designed to serve an important function in human social life? Shouldn't that possibility be tested? Tested before we just attemt to turn depression off, which medical science will get better and better at doing in the next several decades, via combinations of improved drugs, genetic manipulations, and talking therapies that do nothing to address the potential adaptive function of depression? Without understanding what we are turning off, we thwart the adaptation's ability to confer upon people its tremendous, life changing, potential benefits. We'll never know the potential costs of eradicating depression, or more proximately, why current therapies are so ineffective, until we test adaptationist hypotheses. Guess what? We've got one to test!

Here, minor and major depression are explained as a unified, contingently escalating, evolved adaptation for overcoming severe chronic constraints on socioeconomic activity imposed by the individual's social network. The purpose of this site is to promote understanding, principled criticism, and empirical testing of the social navigation model of unipolar depression, also referred to as the "niche change" or "bargaining" model.

In short, major and minor depression, the entire intensity and subtly different flavor spectrums of depression, are proposed to represent a unitary, contingently escalating adaptation to help people overcome highly maladaptive constraints on their status or socioeconomic activity that are stubbornly imposed by their social network.

Dr. Paul J. Watson

Department of Biology, University of New Mexico, Albuquerque, NM, USA

Summary of the Social Navigation Hypothesis of Depression

Complex Contractual Reciprocity: The Matrix Has Us - Understanding unipolar depression, I suggest, depends upon understanding the pan-cultural foundations of human sociality. Humans absolutely depend on diverse social exchange contracts for their survival and reproduction. A principal feature of human sociality is that individuals become deeply embedded in a complex matrix of socioeconomic exchange contracts. This contractual matrix is the basis for the many relationships that are the source of all essential goods and services a person needs to achieve virtually any fitness-related goal. But, this same complex interactive support system entails myriad obligations and expectations. Thus, it easily can become a kind of socioeconomic prison. On occasion, it may keep an individual tied to a societal niche that, for them, has become obsolete and very costly compared to alternative niches that the person could come to occupy, if only they could obtain a properly and usually majorly revised regime of social support.

Our conceptual model of depression, The Social Navigation Hypothesis (SNH) or, as I prefer, The Niche Change Hypothesis, is based on an appreciation of the great seriousness of the fitness dilemma described above and the ease with which such a dilemma can arise in human life as an individual develops. A capacity/opportunity mismatch can develop as a consequence of many major negative life events such as the loss of a valued, socioeconomically important partner or reduced physical or mental capacity. Ironically, a mismatch can stem just as easily from certain positive life events, such coming up with a creative and potentially lucrative idea, becoming pregnant, or given a shot to prove ones-self in a position of higher status and responsibility, if these positive events occur under stubbornly restrictive social conditions that block the person from actually profiting from that event.

Development of the SNH as an explanation of how unipolar depression may address such a personal capacity/opportunity mismatch flows from a “reverse engineering” analysis of the widely-accepted core symptoms of depression - anhedonia and psychomotor perturbation - as well as several of its main risk factors. Reverse engineering of is an important technique for generating functionalist or adaptationist hypotheses in evolutionary biology. It involves inferring the function (adaptive significance) of a trait from an understanding of its design and the structure of potentially relevant reproductive problems faced by the organism in its natural environment during its evolutionary history.

Assessing and Renegotiating Social Contracts: According to the SNH, the overall function of depression is the sober analysis and eradication of a severe socially imposed mismatch between the depressive's current or incipient capacities for fitness-enhancing socioeconomic activities versus their socially sanctioned opportunities. Put more simply, the SNH proposes that depression is a potentially adaptive response to a special social cause of goal frustration. The SNH predicts that major depression, in which symptoms become so intense that they cause involuntary reduction of self-care and socioeconomic performance, should arise when the constraints that are the cause of the mismatch have a broad multi-partner basis in the individual's social network. In other words, the SNH posits that the main evolved trigger for depression consists of the individual being faced with the task of simultaneously overcoming the resistance of many social partners to helping him or her realize important practical (fitness-enhancing) goals that would alleviate a particularly onerous capacity/opportunity mismatch.

So, the SNH argues that major depression evolved to deal with a specific, extraordinarily difficult goal frustration context. Fitness-reducing goal frustration is central to the social navigation hypothesis. Under the SNH, major depression is designed for situations in which there is a goal, importantly related to fitness, that the depressive is chronically blocked from attaining, or maybe even adequately investigating, by a stubborn and diffuse, non-point source of social constraint. This is a special context in which many well-established, complexly interacting social contracts need to be revised all at once, in a coordinated manner, to clear a new more lucrative socioeconomic niche.

The SNH contra-indicates depression as a general response to goal frustration, even if it is severe. Instead, it predicts depression primarily when overcoming goal frustrating situations requires that the person change many resistant minds at once, that is, when goal frustration is due to the mismatched individual being stuck with status quo fitness-pursuits as a result being embedded in a contractual matrix that is, directly or indirectly, co-enforced by many if not all of their social partners, often including intimate friends and loving kin.

The SNH also mainly predicts depression when the restrictive social partners are estimated to have a high degree of dependence on the goal-frustrated or mismatched individual, such that the depressed individual's extortionary leverage is high (see below). Also, the SNH does not predict a consistent relationship between negative life events and depression. People, like any good organism, should be designed by selection to spring back from most negative events, and to not only accept or accommodate most bad situations, but be motivated to make the best of them. So, the kind of social conflict specified above should be the key predictor of depression – costly social conflicts that necessitate complex negotiation and honest signaling of a need for help, and especially conflicts that call for imposing attitude and behavior changing (motivating) costs on many social partners, so as to eventually change their original unfavorable cost-benefit analysis of helping. Overall, the idea is to foster sober incisive social analysis (perhaps this is the main emphasis in relatively covert forms of minor depression), issue an honest signal of need, and to imposed escalating costs on dependent social partners, via self-harm, until a tipping point is reached at which their cost-benefit analysis of helping becomes positive.


Dual Involuntary Elements: Honest Signaling of Need and Fitness Extortion: In the special social context outlined above, it may make adaptive sense to use the across-the-board emotional and physical debilitation of major depression to send a strong convincing honest signal of need, while simultaneously broadcasting an extortionary force amongst all dependent social partners. The genuinely involuntary nature of the entire phenomenon of major depression helps make the extortionary element non-antagonistic, and thus minimizes social partner anger and retaliation.

Depression’s costly symptoms can serve as an honest, involuntarily generated signal of need. Here, depression’s disabling symptoms function to impose costs on the depressed individual, costs that only can be recovered if long-term fitness is truly significantly enhanced by the help consciously or unconsciously being sought. Some social partners may be moved to help by this honest signal of need: those who are willing to invest in the signaler, either in conventional (previously contracted) or novel ways, as long as they have a high degree of assurance that such help really will increase the recipient’s fitness enough to make the work, risk, and sacrifice involved with helping worthwhile.

However, other social partners may exist, who also are key to redressing the depressive’s capacity/opportunity mismatch, who do not see it being in their interest to help even when they perceive a highly credible signal of need. Instead, they see themselves, perhaps unconsciously, as benefiting more by keeping the depressive in their current social niche; these social partners may use a variety of subtle means to attempt to enforce the mismatched individual's status, niche, and means of livelihood. The SNH posits that depression helps deal with this second, more problematic group via its extortionary aspect.

A key inevitable consequence, and possibly the most important adaptive function of major depression, is that the many personal costs suffered by the depressive via psychomotor disturbance and anhedonia automatically inflict costs on all of the depressive's close and dependent social partners, that is, the depressive's "positive fitness correlates." Thus, when the subconscious mental mechanisms that modulate major depression in response to social variables and assessment of the severity and cause of the capacity/opportunity mismatch are activated, they cause the depressive to engage in involuntary, unintentional, and potentially wholly unconscious "fitness extortion."

The extortionary element is central to major depression's adaptive function and the principal evolutionary explanation of major depression's potentially extreme costliness. We postulate that because the depressive's own costs necessarily are broadcast to all social partners in direct proportion to the positive fitness correlation between the depressive and each partner, depression is specifically designed to deal efficiently with constraints on fitness enhancing activity that arise from a broad, “non-point” source in the depressive's social network. Under the SNH a major fitness-enhancing revision in the person’s social niche is usually needed to address their mismatch. The disabilities and costs of depression make more economic sense when many of the positive fitness correlates who are impacted by them are all relevant to helping the depressive overcome their fitness-reducing capacity/opportunity mismatch; depression is an especially efficient means of overcoming a mismatch that requires the re-writing of many social exchange contracts. This is not to say that depression will never occur in association with problems in the subject's life having a "point source," that is, one or a few exceptionally powerful social partners who are mainly responsible for the problematic constraints. However, more often than not, we predict the solution to dealing with a specific point source of constraint will be rooted in the "non-point source," that is, a general unwillingness amongst many of the depressive's social partners to help the depressive effectively deal with the more blatant point source.

Extortionary pressure on social partners, even loving ones, often may be required specifically in the niche change context, because when inter-individual socioeconomic contracts are in flux, which is the case whenever a person pursues a substantive niche revision, it will be especially difficult for positive fitness correlates of the depressive to estimate their payoffs for helping. Moreover, insofar as there is uncertainty or pessimism regarding the expected direct and indirect costs of helping the depressive in meaningful ways, or the long term benefits expected from anticipated post-niche-revision contracts, most social partners will be conservatively biased toward maintaining their status quo contracts with the depressive, and thus perpetuating the depressive's capacity/opportunity mismatch.

One reason for a highly conservative reluctance to help in the specified niche change context, is that since the needed niche revision threatens to impact many relationships (many different contracts), each person in the social network who helps has to worry about how a successful niche change would impact not just the niche changer, but many other people whom they share as social partners. In other words, every potential helper has to consider complicated indirect costs to themselves that could follow from helping the depressive make big changes in their socioeconomic life that make third parties unhappy. The SNH states that major depression's gradually escalating fitness extortion functions to gradually lower the fitness of social partners enough to move them across a fitness threshold, a tipping point, quantitatively unique to each dyad, where their expected net benefits of helping finally outweigh the costs they incur as a consequence of the depressive's inability to function.

By design then, major depression gradually renders the person incapable of fulfilling their normal social and economic roles in their community. Major depression's core symptoms reduce a person’s ability to care for them self and others via (1) anhedonia, a generalized lack of motivation and pleasure, and (2) psychomotor perturbation. The latter may involve either fatigue and reduced mobility, or a level of agitation and irritability that makes ordered productive motor activity very difficult. These subjectively horrible symptoms have largely been the basis for labeling depression as maladaptive and pathological. The SNH suggests that this conclusion is very premature and needs rethinking. Like physical pain, psychological pain is not necessarily maladaptive. Moreover, just because a trait has heavy overt costs does not disqualify it as an evolutionary adaptation if, at least in the ancestral evolutionary environment, on average, it conferred fitness benefits. Under the SNH, the two above-mentioned synergistically disabling and costly symptoms of depression are exactly what give it social problem-solving power.

Suicidality: Depressed individuals are at increased risk of actual and attempted suicide. How could such behavior ever be evolutionarily adaptive, as the SNH implies? The SNH sees explicit suicidality and parasuicidality (i.e. suicide attempts really not intended to cause death) as just a different, possibly more attention-arresting version of the generally reduced levels of self-care imposed by major depression. In other words, the SNH proposes that it was parasuicidal any time a person living in the stone-age environment in which human depression evolved neglected a good chance to take care of his socioeconomic contracts with others, or to directly take care of himself by tending to shelter, food stores, hygiene, etc. Thus, like all these other costly lapses, explicit suicidality potentially serves as an honest signal of need and a means to compel social partners to consider how they might help the depressed individual improve their life circumstances. (See also Posting #2, from 7-19-2008, below.)

Minor Depression: The SNH proposes logically related functional roles for minor and major depression. We operationally define minor depression as a level of depression in which the symptoms can be intentionally hidden from social partners. However, the pain and discomfort of minor depression, as well as its ability to reduce the afflicted individual’s ability to escape thoughts concerning fitness-reducing problems by doing normally pleasant activities (parties, sports, reading, movies, etc.) helps make depression a state in which cognitive and emotional resources are strongly dedicated to problem-solving analysis and negotiation. Under the SNH, minor depression optimizes emotionality and cognition for (1) identifying and analyzing possible mismatch-causing factors within the individual's socioeconomic network and (2) planning active negotiating tactics to ameliorate fitness-hindering constraints. Under our hypothesis, major depression only ensues facultatively if active tactics of negotiation or coercion fail to yield the kinds of investments and concessions from partners required for niche change, that is, for substantive revision of the person’s socioeconomic or political position. Follow Dr. Paul W. Andrews' continuing work on depressive rumination for more on the possible social problem analysis function of depression.

Some work on people in a depressed state indicates that their analytical abilities are reduced, not enhanced. This seems to contradict the SNH. Here, however, is a good example of how the SNH suggests new research paradigms in the study of depression. The SNH proposes that depression forces the indivdiual to focus analytical resources on the fitness-reducing social problem that is causing a major capacity/opportunity mismatch in their lives. It functions to reduce their freedom of attention and their ability to escape from ruminating on this pivotal issue. It makes the usual pleasures of the current social niche, which may serve to keep them maladaptively stuck there, inaccessible. And it makes novel pleasures unattractive as well, again, to make avoidance of the fitness-reducing problem difficult. The SNH predicts that, by design, people in the midst of depression will indeed be less able to solve the kind of standardized arbitrary problems and puzzles typically presented to subjects in traditional psychiatric lab studies. Therefore, an investigator who wishes to look at the analytical abilities of depressives needs to challenge them with tasks that clearly represent some aspect of the specific social problem(s) or capacity/opportunity mismatch that caused their depression in the first place.

The SNH and Anti-Depressant Medications: Whether or not depression is an evolutionary adaptation does matter - its has major implications for how it can, and perhaps how it should be treated. The SNH suggests that conceptualizing unipolar depression strictly in traditional medical terms, that is by simply pathologizing it, typically fails to serve its victims well. A pharmaceutically centered approach often may be severely misguided. Talking therapies that skillfully attempt to convince the depressive that his or her thoughts and emotional states are irrational or unwarranted may also be lacking. The SNH perspective on depression may help explain why it is increasingly epidemic in modern western populations in spite of the fact that these populations are virtually awash in modern anti-depressive medication (such as the many SSRI’s) and cognitive-behavioral oriented psychotherapies. The SNH also helps us see that part of the depression epidemic may be attributable to the extreme dynamism, myriad opportunities, and onerous socioeconomic insecurities of modern social life, which generate high rates of capacity/opportunity mismatching.

The diminished and less durable positive fitness correlations common to many modern societies may have led to more frequent extreme escalations of major depression than in the ancient evolutionary environments, as well as reduced overall effectiveness of depression as an adaptation. If therapists are aware of this, the SNH predicts that they may alleviate depression, when warranted, by helping the person see more clearly that they lack the leverage needed to elicit help from social partners via a depressive strategy. In such a case the therapist may be especially well situated to help start or re-start a more conventional active negotiating strategy to ameliorate fitness-reducing social constraints.

Nevertheless, these mismatches and their causes beg to be addressed with specificity in therapy. The SNH does not altogether condemn the use of medications, but it does predict that depression will be far more responsive in the long run to in-depth, thoughtful, evolutionarily-informed, individually-tailored social problem solving therapy.

More specifically, the SNH would indicate talking therapies specifically aimed at identifying personal mismatches in capacities versus opportunities for fitness-enhancing socioeconomic activities, plausibly caused by constraints imposed by the depressed person’s social network. Once specific hypotheses are generated concerning mismatches and their social cause (a process that may already be of therapeutic value), the talking intervention should move quickly to developing and implementing practical and efficient strategies for overcoming the constraints. Medications should be used in a way that makes this process feasible and reasonably safe, but not unnecessary.

Papers, manuscripts, and interview, available online:


Here is a link, via my colleague Dr. Paul Andrews' web site, to an outstanding paper on the evolution of depression by Drs. Paul W. Andrews and Andy Thomson published in the July 2009 issue of Psychological Review entitled: "The bright side of being blue: Depression as an adaptation for analyzing complex problems."


·        Watson, P.J & Andrews, P.W. 2002.  Toward a revised evolutionary adaptationist analysis of depression: The social navigation hypothesis. Journal of Affective Disorders  72, 1-14.

You can hear PJW in a June 2018 discussion about this theory of depression on Dr. Joe Alcock's excellent wide-ranging Evolutionary Medicine Podcast, specifically podcasts #27 and #28.


·        Hagen, E.H, Watson, P.J, & Thomson, J.A. Love’s labour’s lost: Depression as an evolutionary adaptation to obtain help from those with whom one is in conflict. In prep. resubmission; rejected without review by The Journal of the American Medical Association, The Lancet, The New England Journal of Medicine...


·        The Evolution of Depression - Does It Have A Role? April 3, 2004. All in the Mind, by Natasha Mitchell, Radio National. Guests: Edward H. Hagen, Paul J. Watson, and Daniel Nettle.


·        Cline-Brown, K., and Watson, P.J. 2005. Investigating Major Depressive Disorder from an Evolutionary Adaptationist Perspective: Fitness Hindrances and The Social Navigation Hypothesis. In: Focus on Depression Research, Jeremy T. Devito, editor. Nova Science Publishers, Inc.

·        Hagen, E.H., Watson, P.J., and Hammerstein, P. 2008. Gestures of Despair and Hope: A View on Deliberate Self-harm From Economics and Evolutionary Biology. Biological Theory 3(2), 123-138.

Additional Reading: Besides the Watson & Andrews JAD 72: 1-14 article on the social navigation hypothesis of depression, there are important related contributions to the evolutionary analysis of unipolar depression developed independently by my brilliant colleague, Dr. Edward H. Hagen:  (1) The functions of postpartum depression, (2) The bargaining model of depression.


Dr. Paul W. Andrews continues to perform research on depression as an adaptation to enhance complex problem-solving ability and garner enhanced investment from social partners. One recent paper of his, published in the journal Human Nature (Summer 2006), examines the possible role of adolescent suicidality in leveraging increased investment from parents. See: Parent-offspring conflict and cost-benefit analysis in adolescent suicidal behavior.


Dr. Daniel Nettle published a critique of the Social Navigation Hypothesis in the Journal of Affective Disorders (August 2004), entitled, Evolutionary origins of depression: a review and reformulation.

We have written two responses to Nettle’s article:

1.      Hagen, E.H. and Thomson, J.A. Social navigation hypothesis of depression revisited. Journal of Affective Disorders 83, 285-286.

2.      Watson, P.J. Submitted, rejected without review, Journal of Affective Disorders.


I welcome comments and discussion concerning the Social Navigation and Bargaining Hypotheses of Depression, and related or competing theories. I have begun posting comments sparked by correspondence, as well as items in the news. See links to my new postings, below.

All correspondence will be posted anonymously.

Posting #1 (04/11/2008): Predictions of the Social Navigation Hypothesis in Relation to Major Depression.


Posting #2 (07/19/2008): Remarks on Suicide Prevention based on the SNH and Scott Anderson's 6 July 2008 NYT Magazine article, The Urge to End It All.

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