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Price JS, Gardner R, Erickson M. (2004) Can depression, anxiety and somatisation be understood as appeasement displays? Journal of Affective Disorders, 79, 1-11.

                                   Abstract

We propose a theoretical model in which major depression and its co-morbid disorders are regarded as adaptive communicational states exhibited in both human and non-human species. Specifically, depressive and anxious mood states, fatigue syndrome and somatoform disorders signal appeasement or submission to human conspecifics (members of a same species). We examine this approach in light of game theory formulations of conflict resolution and the triune brain theory of MacLean. We outline approaches to treatment of depression, suggestions for research, and the possibility of a future pathogenesis-focused nosology.

Keywords: depression, evolution, communication, affective disorder, anxiety disorder, somatoform disorder, chronic fatigue syndrome, appeasement, submission

                                Introduction

For over thirty years we have explored the idea that depressive states evolved as part of the yielding or submissive component of agonistic behaviour (social competition) (Price, 1972; Price et al., 1994; Stevens & Price, 2000). In this paper we examine escalation and de-escalation as alternative agonistic strategies, providing normal communicative behavioral states that in some circumstances may manifest as mania and depression, respectively (Gardner, 1982, 1988). We suggest that the three levels of the triune forebrain (MacLean, 1990) each independently make the choice between escalation (fight) and de-escalation (flight or submission). Depressed mood stems from de-escalation at the lowest of the three levels, and tends to occur after frustrated conflict resolution from inappropriate escalation at one or both of the higher levels.

In pursuing this evolutionary argument, we follow a tradition articulated by Robertson in 1890 who "traced back the symptoms of disease to the functions of health, and carried both back to their origin in evolution..." Darwin's book, The Expression of the Emotions in Man and Animals (1873) included descriptions of people melancholically depressed. Modern day versions include D.R. Davis’s suggestion that “The signs and symptoms composing depression represent attempts at adaptation to the immediate circumstances, and reflect adaptive processes that are part of the organism’s ordinary repertoire” (Davis, 1970). Our approach, evolutionary psychiatry (Nesse, 2002), represents one of several attempts to apply adaptationist thinking to psychiatric disorders. In the case of mood disorders, it is likely that a predisposition to depression has been most strongly selected for as it represents a “defence” against attack by conspecifics. More severe or chronic depressions may additionally represent “defects” in the sense of Nesse (2002). Moreover, mismatch between the present and the environments in which the capacity for depression evolved may have resulted in an over-expression of depression at present that exceeds a previous optimum (McGuire and Troisi, 1998). No conflict exists between evolutionary theories of depression that concern why it evolved, and physiological theories that examine why it occurs on any one occasion (particularly the brain processes involved), and psychoanalytic theories focused on development of depressive tendencies in the individual’s ontogeny. Evolutionary theories about adaptive strategies can exist independently of any genetic mechanism by which the strategies are transmitted (Grafen, 1984). The transmission of alternate strategies for dealing with environmental change, their frequencies and payoffs are the subject matter of behavioral ecology (the functional analysis of behaviour) (Krebs & Davies, 1993).

                       The hypothesis

Appeasement displays

Our theory holds that patients suffering from depression, anxiety, and other co-morbid conditions such as fatigue states and somatisation disorders, communicate to their fellow human beings that they are non-combatants in whatever form of social competition the society engages in. When such communication occurs in nonhuman animals, the label of appeasement (or submissive) display indicates it functions to switch off the aggression of the rival. It says, “I am no threat to you, I will not retaliate”.

The observer does not obviously appreciate an appeasement function of depression because the depressed patient does not consciously submit to anyone. To understand unconscious components, the triune brain theory of Paul MacLean may help. MacLean (1990) proposed that during the course of evolution from reptiles through early mammals to late mammals the brain did not enlarge homogeneously, but rather developed a “central processing assembly” at each stage, though these overlap with the older mechanisms remaining active. A reptilian (or “instinctive”) assembly in the basal ganglia makes decisions relating to the social life characteristic of the common ancestor of humans and reptiles, most likely courtship of the opposite sex and agonistic interactions with the same sex. A paleomammalian (or “emotional”) assembly in the limbic system decides on mammalian problems such as family life and attachment behaviour as well as more sophisticated decisions about courtship and agonistic behaviour, taking into account factors not dealt with by the reptilian brain, such as the existence of alliances and family ties. A neomammalian (or “rational”) assembly in the neocortex arrives at “conscious” or “voluntary” decisions about complex matters unknown to the two lower assemblies; it also makes decisions about family life, courtship and agonistic behaviour. As a result, decisions about agonistic behavior are made at three separate levels of the forebrain.

Cannon (1929) first pointed out that organisms do not run at full steam all the time. Great reserves of energy can be called upon when the situation demands. Such situations include non-social events, such as encountering a predator, and in these cases the bodily changes mobilize the body’s resources to fight or flee. Other situations involve competition with conspecifics, when a surge in energy in one competitor (escalation) may tip the balance in an evenly matched confrontation. Likewise flight may terminate a conspecific encounter. A third available strategy of appeasement or submission doesn’t help with a predator but does help in social competition. Whereas the choice of strategies in dealing with a predator involves fighting or fleeing, the more complex strategies available for dealing with a conspecific can be summarized as escalation and de-escalation.

Escalation refers to a switch to a more expensive form of competition; when an individual escalates, the chances of winning increase but the potential costs of losing also increase. In de-escalation, the individual gives up any chance of winning, but reduces the costs of losing. De-escalation may take the form of departure, but in group-living animals submission with appeasement display represents the more common form of de-escalation.

In line with the complexity of social competition, escalation and de-escalation became more complex over the course of evolution. For instance, these behaviors may have become more prolonged: instead of a rapid choice between fight and flight, an interpersonal struggle for dominance may last several months, even in chimpanzees (deWaal, 1988, 1999). And in humans, for whom competition for prestige has largely replaced agonistic competition (Gilbert, 1992; Stevens & Price, 2000, pp. 51-52, 159-160), escalation may take the form of the vigorous pursuit of goals, whereas de-escalation may take the form of giving up goals (see Table 2 at end of paper).

As said above, decisions to escalate or de-escalate take place either simultaneously or consecutively at all three levels of the triune brain (Tables 1 and 2, at end of paper). At the rational, or neomammalian level, the decision consciously and voluntarily either to fight harder or to back off takes place; when backing off, the appeasement display may take the form of a graciously worded apology, or a flowery speech of submission. At the emotional or limbic level, escalation takes the form of anger, indignation and the exhilaration of combat, with its associated bodily changes; de-escalation at this level may recruit the dysphoric emotions of anxiety and the sense of being chastened. Also, since this level involves the rules of group membership and prestige competition, guilt and shame also play roles so the appeasement display typically consists of weeping, blushing, and protestations of repentance (Stein and Bouwer, 1997). At the instinctive level, we hypothesize that escalation in the reptilian brain takes the form of elevated mood, giving the individual a prolonged increase in energy, optimism, self-confidence and heightened sociability all of which function to recruit allies. Conversely, de-escalation at the instinctive level takes the form of depressed mood and may include unfocused anxiety, fatigue and a sense of physical disability. The appeasement display at this level communicates this impairment and disability to any rival or to society as a whole. Parenthetically, when directed at friends and allies, the appeasement display takes the form of a distress signal, sending the message, “I am sick, care for me, and do not send me into the arena to fight on your behalf” (Price & Gardner, 1995). Communications of disability do not appear in awareness for either the sender or receiver. This paper addresses this reptilian level of appeasement display taking place outside consciousness.

Communications emitted by depressed people

 The depressed patient communicates submission to others with such pessimistic statements as follows: “I am a worthless person,” “I have no interest in anything,” “I do not deserve to live.” Audiences include medical caretakers. Signals include more than words, such as agitated pacing, wringing of hands, mute immobility, aversion of gaze, and a melancholic face that include the lines of worry in the forehead. Clinicians also note as well as learn from friends and relatives what signals no longer get emitted. The patient does not swagger, nor flatters others, no longer sings in the bath nor distributes praise to dependents. Widespread inhibition of social initiative represents a prevalent theme.

Normally, a person directs submission to one or more individuals, for example, to a leader, a parent, or God. This applies to the appeasement display of the rational neocortical level. But the depressed patient, communicating at the reptilian level, makes a non-directed, general communication of submissive incapacity. That the person feels incapacity clearly registers for the observer-recipient but not so clearly the non-specific message of submission because the recipient also seems to absorb the core message at a level of brain activity outside awareness. Indeed, the depressed patient takes the expression of submission into a different logical category, by communicating the message, “I am too depressed to even have the capacity to express submission” (Price, 1988).

Various dysphoric states variously communicate submission According to the social competition theory (Gardner, 1982; Price et al., 1994; Gardner, 2001), depression communicates by sending the message, “I am no threat to you, and I am not going to retaliate.” The message may take several forms with each issuing the overall message of subordination. The particular form selected affects manifest diagnosis, as follows:

“I am too depressed to retaliate”…….. depressive illness

“I am too anxious to retaliate” ………. anxiety disorder

“I am too tired to retaliate” …………... chronic fatigue  syndrome

“I am too sick to retaliate” ……………. somatisation disorder

Since these states are all sending the same message of non-retaliation, it is not surprising that there is considerable co-morbidity between them (Kaufman & Charney, 2000; Nemeroff, 2001; Tyrer, 2001).

Treatment implications

We proposed above that all three levels of the triune brain independently make decisions to escalate or de-escalate a conflict (Price, 1998; Cory & Gardner, 2002). The depressive message of non-retaliation represents the de-escalation decision of the lowest level of the forebrain, the reptilian brain. The aim of treatment should focus on allowing the highest level of the brain to manage the situation, parallel to turning up the thermostat for warmth instead of shivering from the body’s lower command structure. The therapist should encourage the patient to send one of the following upper level messages:

 “I have decided not to retaliate further because…….

     “I have already retaliated sufficiently and am satisfied”

     “We have submitted our difference to arbitration and it has been settled”

      “I have reframed our situation and have realised it is not threatening”

      “I decided you are impossible to deal with and have cut off contact”

     “I realised I was in the wrong and have apologised”

When the brain highest level either escalates successfully or de-escalates, the situation has been managed, and the factors eliciting strategy decisions from the lower levels of the brain are no longer active; and since the reptilian message of non-retaliation is no longer needed, the depression remits (Stevens & Price, 2000). Interpersonal Psychotherapy (Klerman et al., 1984; Weissman et al., 2000) already uses this kind of conflict resolution as do other psychotherapies as well. We hope this evolutionary perspective helps clarify the biology that underlies part of the technique’s effect. The formulation differs from that of some psychotherapies because this focuses less on actual symptoms of depression but rather on the real life conflicts that have produced it. After all, should a patient complain of shivering, one doesn’t rub ointment on the shivering muscles, but rather poses the question about why the person doesn’t turn up the central heating.

To summarize, our formulation points out that depression represents a communication disorder because it signals submission on the level of the reptilian brain; by contrast, the healthy person signals with the language-using human part of the brain, and therefore does not need to communicate submission using the pre-language metaphor of sickness. When higher centers fail to handle conflict, lower center responses activate. Treatment therefore helps the patient substitute a conscious, rational and voluntary course of action for an involuntary response that humans share with their reptilian cousins. Parenthetically lizards become sick and not infrequently die when they cannot deal adequately with conflict (MacLean, 1990).

       The use of metaphor in appeasement displays

In this section we hope to show that, by expressing submission with the metaphor of sickness, humans are using a metaphorical style of communication which is widely used in the animal kingdom.

Animals cannot say, “You win!” or “I give up!” or “You are stronger than I am,” and instead they tend to express this message in metaphor. They utilize the fact that some categories of individuals are weaker than others. For instance, small animals are usually weaker than large animals, immature animals are smaller and weaker than their parents, and females are usually weaker than males (although not in some species such as hyenas).

Much animal submission is expressed with the metaphor of size, sending the message, “I am like a small, weak animal to your big, strong animal”, and they use various devices to reduce apparent size. Some lineages use more sophisticated strength imbalances. Thus, canids base their metaphor on the immature/mature difference (Beckoff, 1977). To convey “You are stronger than me”, the wolf behaves like a puppy, and rolls on its back to present its perineal area for cleaning by the “parent.” When an adult male performs this behaviour to another adult male, it conveys in metaphor the message, “I am like a weak puppy to your strong adult wolf.” Old world monkeys by and large do not use the child/adult difference. Instead, they use the sex difference, having evolved the metaphorical communication that says, “I am like a weak female to your strong male”. To convey this, the submitting adult male behaves female-like, offering its genital region to the rival, who may make some token mounting actions, accepting the rival’s expression of a female role, and then complementing it by suggesting the male role in sexual intercourse (Deag, 1977).

Submitting humans use more flexibility. While they use both child/adult and sex differences, they do so to lesser degrees. Variations of the size metaphor are widely used, and have become culturally ritualised (Price & Gardner, 1995). Larger size conveys greater power in that large people are usually stronger than small, and tall people than short. To express dominance, therefore, one may wear a hat for additional height, and then if one wishes to be submissive, the hat may be taken off, or “doffed”, as this then makes the person smaller again. Bowing, kneeling and prostration convey more intense degrees of submission, rendering one progressively shorter. If size-comparisons represent an ancient metaphor (insects and reptiles typically decide contests on the basis of size), the human rational level modifies it with cultural customs.

We suggest that humans frequently deploy the sickness metaphor when communicating submission at the lowest, reptilian level of the forebrain, and then it is likely to appear as co-morbid with depression, anxiety and fatigue. It takes advantage of the fact that sickness means weakness and also elicits compassion in the other person. The message discloses the person as, “a weak sick person to your strong healthy person.” Details of such “sickness” vary, unimportant for signalling the overall message of “I am too sick to retaliate,” but still important for diagnosis and treatment. Thus, the sickness may take the form of “soldier’s heart”, or irritable bowel, or hyperventilation, or fits or faints or tremblings, or of a general prostration. From the point of view of decisions made at multiple levels, these do not represent forms of conscious deception or malingering (in which the sickness metaphor is used at the highest or rational brain level) because the individual truly believes that sickness exists, in fact, so convinced that any suggestion to the contrary receives violent rejection, as observed almost invariably when patients with chronic fatigue learn that the doctor considers them perhaps psychologically rather than physically ill. The metaphor of sickness depends on an archetypal recognition of the sick role, and since it likely evolved before recognition of depression as a legitimate reason for taking the sick role, the metaphor therefore fails to include psychiatric disability. When a physician tells such patients that they are not physically ill, they feel invalidated and not surprisingly reject the opinion.

The diagnosis of out-patient or less serious depression (as opposed to in-patient melancholia) represents a relatively recent Western phenomenon. In most present-day cultures (and in our own past) depression usually received a physical diagnosis, such as neurasthenia or neurosis; indeed, this once implied an organic affliction of the peripheral nerves. Only in our own sophisticated environment do patients need to accept a diagnosis that fails to fit either with the evolved archetype of “madness” or with that of physical illness. Since no archetype of non-psychotic psychiatric illness appears to exist, doctor and patient may both experience confusion and dissatisfaction in a consultation that involves a diagnosis of depressive illness even though widespread public education attempts to change this view. On the other hand, it may meet greater success if it appears to be a medication-responsive condition (hence, a reason for the popularity of the “crooked molecule” metaphor for depression).

In summary, humans now can say, “I submit”, and they have done so since the human use of language. But they also convey the same message in metaphors, perhaps because such dramatic communications originated earlier than verbal communication (Donald, 1991). The submitting person reduces personal size in some symbolic way as mediated by levels of the brain. Also, the point of this article, humans seem to have retained the capacity to communicate submission by the syndrome of depression, mediated by the brain our ancestors shared with the ancestors of present day reptiles. Not uncommonly messages on the same topic issue forth simultaneously on different channels. Sometimes these messages reinforce each other; sometimes they conflict and invalidate each other. Many depressed patients appear to submit using the metaphor of incapacity, while at the same time they may express anger, or they may cling stubbornly to unrealisable goals and unreachable objectives. In this case they de-escalate at the instinctive (basal ganglia) level of the forebrain while they escalate at the emotional (limbic) level with anger, or at the rational (neocortical) level with high aspirations (see Table 1).

      Communication to dependants and loved ones

Even depressed patients do not submit to everyone as seen in the hierarchical situations of workplace and the family. Whereas a depressed manager may appear to “go quiet” to his superiors, his secretary and other underlings may find him irritable or downright aggressive. Histories from family members often reveal a depressed episode in a father or a dominant husband at a time when they experienced him as particularly angry; they failed to see the submissive communications beamed up the hierarchy. This stems from the fact that although depressed patients often fall in the social hierarchy, they do not usually fall to the bottom; hostility expressed to dependants may even be increased, and this serves to prevent the dependants from rebelling.

Loved ones dealing with a depressed person find themselves in complex situations. If allies try to push the patient into life arenas, for instance, the depressed person may work hard to keep them from succeeding because such efforts directly counter the depressive submission. For such reasons, patient often display firm and assertive communications with allies, and may be quite manipulative, as Freud pointed out early (Price and Gardner, 1995). Sir Aubrey Lewis wrote: "Many depressed patients, professing humility, are importunate in their demands to those around them." (Lewis, 1947, p.1885). Aaron Beck (1974) warned us not to “lock horns” with a depressed patient, in case we get pushed right out of the office. The theory presented here shows it to stem from the patient’s own agenda of submission and when that differs from the attitude of their allies, they nevertheless firmly maintain and express their countering point of view. Indeed, part of the effectiveness of the depressive reaction as a form of submission stems from the conviction that things will not get better or even that they should not get better. The lack of hope of, or desire for, recovery, possesses “design” features. It communicates no preparation whatsoever for a “come-back”. Hence, depressed patients display high motivation to refuse treatment.

Escalation and de-escalation at three brain levels: an illustration

We have not said much about de-escalation at the limbic level, characterised by depressed emotion. Depressed emotion has an object; that is, one is depressed about something, and if the situation changes for the better, one cheers up; also, depressed emotion does not have the pervasive quality of depressed mood. It has been suggested that depressed emotion has the function of helping one to abandon unrealistic goals (Champion & Power, 1995) or to change from a depressing niche to a more satisfactory one (Watson & Andrews, in press).

A clinical example from English country life illustrates how sequential decision-making, or strategy selection, works normally at the three levels of the triune forebrain in relation to goal change, niche change, and the transfer of both power and goal-attainment from one individual to another (condensed from Price, 1998). If the Lord of the Manor dies, custom dictates that his widow hands over the manor house to the wife of her eldest son, whereupon the widow moves to the dower house, a less prestigious dwelling. This move taking place shows a voluntary acceptance of reduced status, and represents a de-escalation at the rational level. But if the dowager decides instead to escalate, she may stay in the manor house rationalizing, for example, that the daughter-in-law possesses insufficient experience to run a large house. But then she feels stress because the daughter-in-law and other family members point out that this deviates from custom. This stressor invokes the limbic escalation/de-escalation strategy set. If she de-escalates at the limbic level, she experiences depressed emotion from the criticism; this depressed emotion may make her less confident about running the manor house herself, and induce her to de-escalate at the rational level by moving to the dower house. If she does this, she has achieved a change to a more appropriate niche, by giving up the unachievable goal of staying in the manor house, and substituting the achievable goal of moving to the dower house. Alternatively, she may escalate at the limbic level, and become angry at her daughter-in-law, possibly describing her to friends as a presumptuous young place-seeker. Successful escalation at the limbic level would result in the daughter-in-law giving up plans to move to the manor house.

But let us imagine that the daughter-in-law is made of sterner stuff, and has no intention of giving up her right to the manor house. Further stress for the dowager then likely ensues; for instance, the daughter-in-law may send a firm of architects into the manor house to plan structural changes. This move on the dowager may cause her to access her instinctive strategy set. Now if the dowager develops mood elevation, she might take legal action against the daughter-in-law, along with mobilizing community opinion against her by active lobbying; such a result in fact represents a common basis for family feuds. Yet, on the other hand, she may instead de-escalate at the instinctive level, and become depressed; if physical symptoms constitute part of the picture, the situation may resolve by her moving, not to the dower house, but to a nursing home. As a result of this instinctive de-escalation, the dowager may give up all her goals, while the daughter-in-law achieves her goal. The unspoken communication from dowager to daughter-in-law goes, “I am too sick to remain in the manor house. You take it.”

This illustration underlines the importance of distinguishing between depressed emotion and depressed mood. Although subjectively and even objectively similar, these two levels of de-escalation have different functions; depressed emotion has the intrapersonal function of regulating the individual’s goal choice and niche selection, whereas depressed mood has the interpersonal function of transferring goal pursuit from the depressed individual to a rival; both depressed emotion and depressed mood facilitate de-escalation at the rational level, and if this de-escalation occurs, conflict resolution is likely to be achieved.

                     Implications for research

If depression represents a component of submissive behaviour, and thus an alternative strategy for dealing with social competition, the study of depressive disorders ought to be a part of behavioural ecology, and the search for the neural basis of depression should be a part of neuroethology. This would enable the considerable research into animal defeat reactions to be made relevant to psychiatry, whereas currently they tend to be part of gastroenterological or cardiological research due to the intestinal ulcers and cardiac problems which are easier to measure than the psychological distress of the defeated animals.

Brain level of the depressive mechanism

Following Bowlby’s pioneering work (1973), many theories of depression depict its function as connected to separation and loss. Since mammals first evolved reactions to separation, this idea places mood controlling mechanisms in the limbic system or higher. Contrariwise, if the mood change originated as part of the agonistic behaviour system, the mechanism must reside in the reptilian forebrain or below. In support of this possibility, Bejjani et al (1999) reported electrical stimulation in the basal ganglia induced depression. Shah et al. (2002) reported striatal atrophy in depression. As yet we do not know whether these changes affect the primary mood controlling mechanism or merely the executive module of de-escalation.

Many common adaptations evolve many times over, sometimes using different mechanisms and structures for a same function (convergent evolution). But, in the case of agonistic behaviour, its likely adaptive expression in every generation since the common ancestor of humans and reptiles makes it probable that the genomic and neural hardware reflect parallel inheritances in humans and lizard, both reflecting a submission repertoire already developed in an ancestor held in common by humans and reptiles.

Components of the reptilian de-escalating strategy.

The appeasement display comprises only one component of the reptilian de-escalating strategy. Another important component is inhibition of attack, reflecting the fact that the appeasement display is an honest signal. The third component is the introduction of bias towards de-escalation at the higher levels, especially the rational level. Depressed mood commonly gives rise to depressive thinking such as pessimism, low self-esteem, a reduced sense of entitlement, and the feeling that things are not worth fighting for; this affects the rational decision-making process, inclining it towards de-escalation. It may be significant that this depressive thinking affects the main variables which have been found by ethologists to determine attack versus escape in pair-wise contests; namely, resource-holding potential (a measure of self-esteem), resource value (a measure of the value of what is being fought about), and ownership of territory (which gives a sense of entitlement) (Gardner & Price, 1996). Thus reptilian de-escalation functions in interpersonal appeasement as well as in intrapsychic functions through which rational thinking gains a pessimistic cast. Frontostriatal circuitry (Rogers et al., 1998) may well mediate this latter function.

Relating to hostility often expressed in depression, this theory predicts that an important variable hinges on the relative status of the patient to the object of the hostility (Stevens and Price, 2000). Although most of the large amount of research on this clinical disorder ignores this variable, future research should take it into account to give findings full relevance. Research into the thinking of depressed patients reveals depressive cognitions involving ideas of being trapped and defeated (Gilbert, 2000; Gilbert et al., in press). These suggest that the evolved mechanisms for helping animals accommodate and respond to defeats may importantly regulate positive affect and reduce exploration of and engagement with the environment. Stevens and Price (2000) discuss other implications of this theory for research findings and projects.

              Implications for classification

The foregoing largely makes this approach one that pathophysiologically lumps diagnostic categories rather than splitting them. Thus, the following are lumped in the single category of appeasement display: social anxiety, depression, chronic fatigue syndrome and somatization disorder. However, the theory also bears on the century old debate over the classification of depressive states into endogenous and reactive varieties; another wording distinguishes between neurotic and psychotic types. In this debate this communicational theory supports the splitters. When viewing depression as an appeasement display, two very different circumstances cause its manifestation, (1) rank change, and (2) confirmation of low rank (a homeostatic mechanism). In the first an individual falls in rank, having lost a contest with an equal or former subordinate thus creating asymmetry, or reversing an existing asymmetry in social relations. In the contrasting second situation, a subordinate may be crushed by a superior for one of many reasons; here this confirms an existing asymmetry, and the exchange furthers the previous homeostasis (Price, 1991).

With loss of rank, change results from a contest with an unclear outcome; either two equals have fought, or a subordinate has challenged a higher ranking individual. The strategy to be adopted (escalation or de-escalation) depends on the strategy adopted by the rival: it pays to escalate if the rival de-escalates, but to de-escalate if the rival has greater powers of escalation, a quantity not usually known at the beginning of a contest (Maynard Smith & Harper, 1988). Game theory provides the appropriate model for this, either the hawk/dove game or the “war of attrition” (Maynard Smith, 1982). The individual chooses between elevation and depression of mood; thus the situation possesses similarities to bipolar disorder.

When the depression serves to confirm low rank, no “game” occurs, and nothing in the situation suggests elevation of mood might result. This does not represent a choice of strategy, but a simple response to stress. The relevant model, one of homeostasis, hinges on what can be called the Resource Gap, a sense of control and superiority that a higher ranking person feels in relation to a lower ranking person. The size of the gap seems to need homeostatic maintenance via boosting and putting-down signals emitted by the higher ranker to the person lower. The higher ranking person tries to maintain the lower ranking person in a sufficient state of inferiority to inhibit challenge, but not too depressed to carry out duties appropriate to the inferior role. Here the appeasement display carries, not only the message, “I am too depressed to retaliate”, but also the additional message, “If you make me more depressed, I won’t be able to function”.

In any species with a hierarchical social organisation, both of these two categories of appeasement display likely exist. The zoologist who first described social hierarchy noted two distinct types of depression in the domestic hen, a severe depression in a deposed alpha bird, and a chronic sense of “hopelessness” in the low ranking bird (Schjelderup-Ebbe, 1935).

In both change and homeostatic depression appeasement functions similarly; therefore, manifest impairment of function, and the expression of pessimistic ideas about the self, the world and the future, represent expressions appropriate for both. On the other hand, the theory predicts different ideas about the past. The “change” depressive formerly possessed higher rank and he might aspire to regain it; but if delusional distortion of the past holds center stage, the patient may deny ever having had higher rank, honours or wealth; the person subjectively feels nothing exists to regain. This means a lessened likelihood of attempted comeback; the appeasement function of depression would therefore have worked more effectively. The homeostatic depressive, on the other hand, never had higher rank, and so depressive delusions about the past would have no function.

Another difference between the two types of depression shows up in the accounts of relatives and friends. Relatives of the “change” depressive tend to notice a change of personality and make comments such as, “He just isn’t the man I married”, whereas the relatives of the “homeostatic” depressive notice little change, making comments such as, “He is much the same as he has always been, only more so.” We predict that construction and application of rating scales based on these considerations should produce a bimodal distribution of scores.

                         Ideological considerations

Evolutionary psychology and psychiatry have been attacked in recent years on general grounds, partly that they face up to human inequality (Kurzban, 2002). Mistaking “is” for “ought,” critics worry that the recognition of widespread social inequality in nature will justify it for those who wish to oppress other people, as occurred with “Social Darwinism.” The theory described here hinges on the possible depressogenic effects of an existing and widespread mechanism for creating social inequality, i.e., social competition that has subserved sexual selection (Price, 1999). But to study something does not indicate approving it. In view of past criticisms, some points need clarifying: for example, social equality and affiliation between members of the same sex represent extremely rare phenomena in non-human animals. But both commonly occur together in human beings, and we suggest that this represents as much a peak of success in our evolutionary history as do human cognitive achievements. Moreover, in addition to coercive inequality, we exhibit inequality based on respect and even hero-worship, associated with joy rather than oppression and depression. But we emphasize that we do not approve of coercive inequality any more than a microbiologist approves of the pathogenic germs he studies.

In an otherwise excellent paper on the possible adaptive values of depressive states, Klerman (1974) refused to discuss the social competition theory on the grounds that depressed patients have enough stigma to cope with without being categorised as “losers.” Countering this, we feel that clinicians should not avert their eyes from the lesions, however distasteful. Moreover, to lose gracefully is no disgrace, and the theory encourages clinicians to foster such decisions in their patients.

                             Summary

This paper presents depression as having evolved as a part of the submissive component of agonistic behaviour over the past 300 million years, and having survived as a failsafe mechanism or safety net as back-up to more recently evolved mechanisms of submission. Of course, mammalian, primate and then human interactions changed dramatically over this time, but connections between depressed mood and submission regularly show up in patients and this formulation suggests possibilities for research, classification and treatment. McKinney and Tucker (2001) suggest that psychiatry should redevelop as a “relationship focused enterprise grounded in sociophysiology to encompass complex behaviors, especially communication, ancient reaction patterns, brain functions, cellular actions and genomic mechanisms.” Rohde (2001) notes the almost total absence of a normal sociophysiology of hierarchical behaviour (including escalation and de-escalation strategies). Yet such descriptions need doing, part of an eventual outline of a sociophysiological basic science of psychiatry that includes the affective disorders, especially since these demand major time and attention of psychiatrists and other clinical human specialists (Gardner, 2001).

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Table 1

Escalating and de-escalating strategies at three brain levels:  agonistic competition

The triune model for escalation/de-escalation

                                         Escalate                                De-escalate

Rational level             Decide to fight on          Decide to back off

(isocortex)                    (stubbornness                 (submission or

                                     courage)                           escape)

Emotional level            Feel assertive,               Feel inferior

(limbic system)            angry, hostile                (depressed,

                                                                          anxious emotion)

Instinctive level             Elevated mood             Depressed mood

(basal ganglia)

Table 2

Escalating and de-escalating strategies at three brain levels:  prestige competition

The triune model for escalation/de-escalation

                                         Escalate                                De-escalate

Rational level            Adopt new goals                Give up goals

(isocortex)                 pursue existing goals            efface oneself

                                 assert oneself

Emotional level         Feel assertive,             Feel inferior

(limbic system)        exhilarated,                      (shame, guilt,

                                 enthusiastic                  sense of failure)

Instinctive level       Elevated mood        Depressed mood

(basal ganglia)

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