Evolutionary theory and cross species comparisons are employed to review responses to traumatic entrapment reactions ( including hostage, domestic abuse and similar situations), their relationship to complex PTSD and to illustrate the relevance of this approach to the study of PTSD. Such victims may display paradoxically positive orientations to their oppressors. Similar responses are observed in many mammalian species, especially primates. Appeasement is the defence most relevant to the survival challenge presented and appears the essence of complex PTSD. Concepts including dominance hierarchies, reverted escape, de-escalation and conditional reconciliation are illustrated. The biological basis of defensive behaviors underlying PTSD is explored with reference to the triune brain. An evolutionary perspective may bridge those of the biological and social sciences.

Introduction

Rapid advances in neuroscientific research have tremendous potential to advance psychiatry. However, curiously little attention has been paid to the broader functions of genes, the foundations on which neuroscience stands. Genes from a proximal perspective are often associated with disadvantage and illness. Both psychiatry and neurology deal with the brain. Neurological illnesses with genetic influences tend to be associated with lifetime prevalence rates in the order of 1-4 per ten thousand. In contrast most psychiatric illnesses have prevalence rates of 1-10 per hundred (Wilson, 1993). While the former prevalence rates suggest diseases, the latter beg the question of whether they might constitute illnesses based on ancestral adaptations. Darwin’s primary focus was on the distal functions of genes in evolution and that too is our perspective.

So why have disadvantageous psychiatric illnesses not died out over time? Possibly, there simply has been insufficient passage of time (McGuire, Marks, Nesse & Triosi, 1992). However, that does not account for the high frequencies of psychiatric illnesses, which are better explained by the supposition that in earlier times these illnesses were adaptive, facilitating survival in the environments of then and there. Most mutations are maladaptive (disadvantageous) and sooner or later die out, but a small minority bring adaptive change and the individuals possessing these genes survive their struggles with their environments at higher rates those lacking such favourable mutations, and whose phenotype lags behind the changing environmental conditions. They may become extinct either by way of a gradual population decline, or a sudden (punctuated) crash due to a catastrophic mismatch of attributes with the contemporary environment. The current doomsday forecasts of global warming would be an example of the latter.

In these relatively civilized times posttraumatic stress disorder (PTSD) viewed from this perspective would usually be maladaptive. However, even in present time PTSD might be adaptive. Take miners or police officers that have had near fatal work experiences. Might their being forced by PTSD to change their occupations not be adaptive in terms of genetic survival? The potential adaptiveness of PTSD in present (or recent) time of soldiers in World War I was such that ‘shell shock’ was frequently viewed as

malingering – with the implication that it was of obvious benefit to the individual rather than to the group as a whole (Wessely, 2003).

While much has been written on evolutionary theories of depression, anxiety and other psychiatric disorders (see Stevens & Price, 1996 and Stein, 2006 for bibliographies) far less has been written on evolution and PTSD (e.g. Bearhs, 1990, Silove, 1998 and Bracha, 2006). The first author of this paper (CC) recently proposed a comprehensive theory of PTSD (Cantor, 2005). The theory in essence

suggests that PTSD is a disorder of the six mammalian defences complemented by vigilance and risk assessment, operating on high alert over extended periods. The theory emphasises that most of Homo sapiens’ genes evolved millions of years prior to the advent of the first hominid (upright great ape) of five million years ago. Homo sapiens is a very recent arrival of about 150 000 years ago. Fundamental survival behaviors such as breathing, eating, drinking and those involved in reproduction are highly conserved throughout the animal world (Cantor, 2005). They did their jobs effectively and their jobs were so central to survival that major mutations affecting these functions would have tended to be fatal. Another fundamental survival behavior (collectively) is defence. Hence, across species comparisons may be revealing.

Where there is considerable behavioral similarity across species, particularly closely related species, the possibility of common phyologenetic origins and functions of those behaviors arises. However, caution needs to be exercised not to take such assumptions for granted as behavioral similarity can evolve without phylogenetic linkage, through convergence and other forms of homoplasy – similarity not based on ancestry (Stearns & Hoekstra, 2000). An example of convergence are the distantly related humming-bird and humming-bird hawk moth which behave remarkably similarly when feeding, hovering extending particularly long tongues as perhaps the only solution for feeding from flowers with deep trumpet inlets without support structures.

This paper has two aims: first, it proposes an evolutionary theory of complex PTSD arising from severe traumatic reactions specific to those trapped in traumatic subordinate relationships, with oppressors wielding much greater power and preparedness to use this ruthlessly. These situations include sieges, concentration camps, wartime prisons, torture, kidnapping, abusive cults and domestic abuse of partners and children. Second, we illustrate the relevance of evolutionary theory and cross species comparisons generally to PTSD research. We will proceed by setting the scene of traumatic entrapment and the Stockholm Syndrome, explaining their relevance to complex PTSD, illustrating related defensive phenomena in other species, before suggesting a neuroscientific model for both research and clinical practice.

Complex PTSD

Judith Herman’s (1992) landmark paper noted that “...prolonged, repeated trauma can occur only where the victim is in a state of captivity, unable to flee, and under the control of the perpetrator.” She described the result as ‘Complex PTSD’. Compared with ordinary PTSD, complex PTSD involves more complex,

diffuse and tenacious symptoms, characteristic personality changes, and vulnerability to repeated harm, both self-inflicted and by the hands of others. The DSM-IV PTSD Field Trial referred to complex PTSD as ‘disorders of extreme stress not otherwise specified’ (DESNOS), its components being alterations in regulating affective arousal (e.g. anger, self-destructive and sexual behaviors), alterations in attention and consciousness (e.g. dissociation), somatization, characterological changes (e.g. chronic guilt and shame, idealization of abusers, difficulties with trust and a tendency to revictimization) and alterations in systems of meaning (van der Kolk, 1996).

Traumatic entrapment

Many people have been traumatized in the recent Iraq war and other global conflicts. Amongst these will be some who have been held hostage. Hostage captor relationships involve massive power imbalances. Torture may be involved and is associated with high levels of posttraumatic stress disorder (PTSD) (Silove, Steel, McGorry, Miles, & Drobny, 2002). This is particularly so if victims are caught unprepared (Basoglu, Mineka, Paker, Aker, Livanou, & Gok, 1997) and if torture involves sexual assault (van Velsen, Gorst-Unsworth & Turner, 1996). Domestic abuse often shares the oppressive relationship orientations of hostage and torture experiences. These experiences may be associated with the development of the Stockholm Syndrome in which victims may not only comply with their abusers but at times even idealize them.

Allodi (1994) described the characteristics of hostage experiences. In prolonged captivity sensory deprivation is usually induced through blindfolding and isolation. Unhygienic conditions, physical abuse, threats of impending death, powerlessness, dehumanisation, humiliation and the need to avoid incurring

further wrath of their captors are characteristic. Captors cultivate hostile environments involving total domination to massively disempower their victims (Symonds, 1975). Threats may be vague and incomprehensible adding to the unpredictability of the experience (Goddard and Stanley, 1994) – unpredictability being a potent inducer of anxiety in mammals generally (Mineka and Hendersen, 1985).

The civilian case of Patty Hearst is illustrative. In 1974 Patty Hearst was kidnapped from her wealthy American family by the Symbionese Liberation Army (SLA), who kept her blindfolded in two small closets for two months, subjecting her to sensory deprivation, rapes and repeated threats of death (Hearst and Moscow, 1982). In two months she was allowed out of the closet for two baths and on “lucky” days the door to her closet was left open for fresh air, when she would hear her captives voicing propaganda. After two months in the closets she was too weak to flee and faced numerous fit heavily armed captors. Finally, before she appeared to capitulate, she was offered a choice - she could leave the closet and go free, or she could join the SLA. She knew from former interrogations that to request the former meant she would be killed, so she requested to join them so that she might live at least for the present. However, there was another final humiliation. She was told that her joining was contingent on her persuading every group member of her worthiness to be accepted into the group. Having earned group acceptance she was forced to participate in lawbreaking, including her infamous bank robbery for which she was convicted (and many years later pardoned). She is said to have developed PTSD with a dissociative pseudo-identity, Pearl (West and Martin, 1994).

The Stockholm Syndrome

The ‘Stockholm Syndrome’ refers to the paradoxical development of reciprocal positive feelings between hostages and their captors, which may enhance the captives coping with their traumatic experiences

(Auerbach, Kiesler, Strentz, Schmidt & Serio, 1994). The Stockholm Syndrome originally referred to a 1973 bank robbery in Stockholm, in which four hostages were held captive for several days (Strentz, 1979). Following release the hostages displayed paradoxical positive feelings towards their captors, and to a lesser extent the captors to their hostages. The hostages defended their captors, condemning the police, their rescuers. One female hostage subsequently developed an intimate relationship with one of her captors. Coincidentally, in 1974 Stockholm witnessed another siege at the Embassy of the Federal Republic of Germany in which again one hostage expressed sympathy with his captors (Gachnochi and Skurnik, 1992).

In another incident, criminals discovered an undercover police agent in their midst. The leader of the criminals left instructions that the agent be killed, if he (the leader) did not phone in to confirm his successful escape. The phone call followed, the agent lived, but subsequently resisted testifying against the leader for several years, feeling that the leader had saved his life (Kuleshnyk, 1984).

The development of the Stockholm syndrome in hostages is considered protective, with the paradoxical bonds opposing the captors’ inclinations to kill their hostages. The longer the siege, the more likely it is that the syndrome will develop (Kuleshnyk, 1984). However, in prolonged sieges police may be unable to trust hostages who may become unreliable witnesses (Turco, 1987).

Four conditions have been suggested as the basis for the formation of the Stockholm Syndrome: perceived threat to one’s physical or psychological survival at the hands of an abuser(s); perceived small kindnesses from the abuser to the victim; isolation from perspectives other than those of the abuser; and the perceived inescapability of the situation (Carver, 2005).

In Sardinia (Italy) kidnapping is common and was associated with 21 per cent mortality for the period 1960-1980 (Favoro, Degortes, Colombo & Santonastaso, 2000). PTSD was found in as many as 45.9 per cent of former captives, similar to that associated with concentration camps and torture. While the number of humiliating and deprivation experiences predicted the development of the Stockholm syndrome, they did not predict PTSD (nor major depression), suggesting that the Stockholm syndrome has important differences from PTSD.

Suggested explanations for the Stockholm syndrome have included identification with the aggressor and introjection of the valued attributes of the captor (Goddard and Stanley, 1994). Victims may regress, identifying with their captors as a child might identify with an abusive parent (Kuleshnyk, 1984). Cognitive dissonance is also thought to be involved (Carver, 2005). The victim strives to reduce emotional discomfort arising from contradictory cognitions by bending those cognitions to accommodate the situation – e.g. the “all husbands beat their wives” perspective. As is wont in cognitive psychology this may be causal or largely an echo of inner experiences. Brainwashing has also been suggested as an explanation. This usually involves captives being repeatedly debased and threatened with death or other grave consequences, if they do not confess their inferior and shameful status. Termination of this torture requires compliance with the oppressors.

The Stockholm syndrome has been experimentally tested from the perspective of interpersonal theory, using simulated captivity. (Auerbach, Kiesler, Strentz, Schmidt & Serio, 1994). This involved two central interpersonal dimensions - control (dominance-submission) and affiliation (friendliness-hostility). The less the ‘hostages’ perceived the simulated terrorists as dominant and the more they perceived them as friendly, the better was the hostage adjustment. Also the more terrorists perceived their hostages as friendly, the better the experience was for the hostages.

Both the Stockholm Syndrome and complex-PTSD share the central characteristic of a seemingly paradoxical idealization of the abuser. It is this phenomenon on which we will now focus from an evolutionary perspective.

Appeasement - a mammalian defence

Cantor (2005) proposed a model of PTSDs (plural) as over-activated mammalian defensive states of ancient evolutionary origin. Psychiatry has neglected the study of mammalian defences, commonly

grossly oversimplifying them as ‘fight or flight’ (Bracha, Ralston, Matsukawa, Williams & Bracha, 2004). There are six major mammalian groups of defensive behaviors, all of which are to be found in exaggerated state in PTSD (Cantor, 2005). A logical sequence for approaching defences recognizes the needs for energy conservation and minimization of risks of injuries. Accordingly, the first defence is avoidance of threats, followed in approximate order of proximity to the threat by attentive immobility (freezing as a prelude to definitive action), withdrawal (not limited to flight), aggressive defence (including fight), appeasement and tonic immobility. The latter is a physiologically different form of freezing to attentive immobility. It is the final defence typically employed when a predator is about to eat its prey. The victim by freezing may yet deter the predator by confusing it, inhibiting its attack reflex and simulating dead and possibly contaminated meat. Traumatic entrapment situations are by definition ones that are beyond the avoidance stage, withdrawal may be desired but is not possible and aggressive defence is not viable because of much lesser status. This leaves appeasement and possibly tonic immobility as potentially more relevant. Our work on tonic immobility remains in progress, but suggests a much lesser contribution, so the present focus continues with appeasement.

Most of these defences are found in the DSM-IV PTSD criteria. Re-experiencing phenomena represent exaggerated recall of threats – the inability to forget (Silove, 1998, Cantor, 2005). Heightened memory would be a prerequisite for learning a more defensive strategy. Avoidance behaviors are clearly defensive even though the DSM grouping confuses true avoidance, withdrawal (flight) and numbing phenomena. Overarousal symptoms may represent hypervigilance phenomena plus aggressive defence

(irritability/anger). Hypervigilance in psychiatry tends to be interpreted in its physiological sense, but in zoological ecology it relates more to heightened scanning for sources of threat.

Appeasement comprises elements of pacification, conciliation and submission. It is primarily a defence

strategy relevant only to conspecifics (one’s own species) and mostly confined to group living (as opposed to territorial) species. It is generally an irrelevant response to predators, in contrast to all the other mammalian defences in which predation threat has figured prominently in their evolution. Appeasement is activated by situations in which subordinate individuals are under close and serious threats from dominants, when withdrawal and aggressive defence would escalate the risks. Appeasement serves a de-escalating function (Price, Sloman, Gardner, Gilbert, & Rhode, 1994, Price, Gardner & Erickson, 2004 and Cantor, 2005). The appeaser relinquishes his chances of winning the contest but decreases the cost of losing.

Appeasement tends to be expressed in metaphor. For instance, sexual gestures of subordinate male monkeys to dominants convey the message, “I am like a weak female”, and the infantile gestures of subordinate adult wolves convey the message, “I am like a weak infant”. It seems likely that human appeasement has come to be expressed with the metaphor of sickness, conveying the message, “I am like a weak sick person” (Price, Gardner & Erickson, 2004). Somatic symptoms of PTSD should be viewed with this in mind.

Appeasement in chimpanzees

Studies of contemporary primates provide clues as to how affiliative tendencies may have become associated with coercive control situations in our hominid ancestors. Ethopharmacologist Michael Chance noted that, after being attacked, monkeys and apes tend to turn to the attacker for comfort and safety. He called this ‘reverted escape’, because after running away from the attack the attacked animal returns, or reverts, to the attacker rather than turning to another member of the group for succor. This observation has been confirmed by recent work on ‘post conflict anxiety’ in chimpanzees (measured by self-directed behavior such as scratching) (Aureli & De Waal, 2000). After a fight both contestants show anxiety, especially the loser, and this anxiety appears to be assuaged by affiliative behavior (e.g. hugging and kissing) between the two former contestants. This makes sense, because if the defeated animal turned to another group member for comfort, this might be interpreted by the victor as a request for agonistic support in preparation for a come-back.

Anxiety complements depression in promoting reconciliation after conflict: the goal of anxiety is safety (Woody and Rachman, 1994), and whereas depression demotivates the loser from desiring to regain his former rank (Price et al., 2004), anxiety may promote affiliation with the winner, leading to conditional reconciliation (reconciliation conditional on acceptance of the new rank order by the loser) (de Waal, 1988). This willingness to accept comfort from an individual that has just beaten another up is important for cohesion in chimpanzee groups, in which males are mostly brothers, half-brothers or cousins, have lived together all their lives, and in which subordinate males are subjected to potentially unlimited aggression from dominants. Females can leave the group, and usually do so around puberty, while males stay in the same group all their lives and reject males from other groups.

To reproduce the male chimpanzee, confined to his group, has to maintain a position in the hierarchy, which is partly achieved by intimidating those ranking below him, and partly by forging alliances with both subordinates and dominants (de Waal and Harcourt, 1992). In this highly social species the restoration of cooperation following conflict is important for group cohesion and defence against predators or out-group conspecifics (Aureli and Schaffner, 2006). If the common ancestor of humans and chimpanzees had a similar social structure to present day chimpanzees, we can see how the infliction of punishment onto defenceless human victims is compatible with the development of affiliation between them.

From chimpanzees to human entrapment

These chimpanzee appeasement behaviors contrast with usual human experiences whereby an oppressed individual can seek solace from others within a larger, multigenerational and dual sexed group, or even these days from outside the group. However, in the closed environment of a hostage situation the hostage may have only dominant oppressors to turn to (reverted escape). Even approaching the leader over a dispute with an intermediate ranking guard may be perilous. Similarly, being seen to seek comfort from other hostages may be interpreted as insubordination.

In hunter-gatherers women have been remarkably frequently kidnapped by opposing tribes, with little likelihood of rescue. From an evolutionary perspective defiance in such circumstances carries the prospect of death and the non-transmission of such defiant genetic traits. Defection by way of submission may promote genetic survival. This has been described as 'capture-bonding' (Henson, 2002). Thus the transmission of genes for appeasement may have been facilitated.

Appeasement is also activated in situations of domestic abuse. The abused child or partner, like the hostage, may accept their subordinate status and the values of their abusers. The battered wife may undergo conditional reconciliation with her oppressive partner, perhaps by a tearful childlike display of inferiority or flirtatiousness (behaviors remarkably similar to those observed in chimpanzees). Furthermore, she had best not be seen later turning to her friends for comfort. Herman (1992) noted, "To the chronically traumatized person, any independent action is insubordination, which carries the risk of dire punishment." Police are highly aware of the risks associated with rescuing victims of acute domestic violence, who may turn on their rescuers displaying apparently paradoxical loyalty to their oppressors, with whom they usually have to continue living.

Sexual abuse of young children and adult humans may at times be associated with degrees of compliance that again seem paradoxical in the extreme to our civilized minds. As observed in primates, a sexual offering may appease the oppressive dominant individual. Adult stalking victims may at times ‘consent’ to sexual intercourse with their stalkers in desperate attempts to pacify them. This compliance is simply a manifestation in our own species of reverted escape fulfilling the appeasement function. Submitting humans may use diverse and flexible behavioral strategies including shrinkage in size, infantile and sexual behaviors as suits the situation (Price et al, 2004).

Appeasement is associated with the emotions fear and shame (Keltner, Young & Buswell, 1997). Fear motivates defence; shame signals “no threat.” Shame is an emotion that is so uncomfortable to the self

that dissociation is often involved when it emerges in the context of PTSD (van der Kolk and McFarlane, 1996). Shame is common in rape victims who not only experience terror, but also may blame themselves

for their humiliation. It also arises in the context of survivor guilt, in which individuals feel guilty for surviving traumas when others did not.

In summary, the study of traumatic entrapment of humans is greatly assisted by understanding mammalian defences. In particular, PTSD associated with traumatic entrapment appears to be associated with an exaggerated appeasement reaction, when viewed from the perspective of 21^st century civilization. It becomes readily understandable when viewed from an evolutionary perspective of reactions that might be expected from a highly sociable mammal with an unprecedented capacity for reasoning, but whose behaviors remain steered by survival instincts. Appeasement needs to be understood as arising in the context of social hierarchies of closed groups, in which subordinate individuals may turn to their oppressor for conditional reconciliation as a de-escalation strategy.

Neurobiology, evolutionary psychology and the social sciences

Evolutionary psychology has great potential to bridge the gulf between neurobiology and the social sciences. Neuroanatomy, neurochemistry and genetics can be related to social function. The early study of PTSD was heavily socially orientated but currently is facing an unprecedented neurobiological swing. The following section demonstrates how the two sciences can be simultaneously understood, with new insights. Evolutionary psychology has even been referred to as ‘sociophysiology’ (Gardner, 1997). However, Panksepp (2006) has emphasised the importance of evolutionary psychology and neurobiology

working in tandem. The former without the latter may constitute ‘just so stories’ and neourobiology without understanding potential evolutionary functions may miss the big picture.

Whilst Papez had already proposed a mechanism of emotion based on the connection of the hippocampal formation with the hypothalamus, it was the follow on work of Paul MacLean that developed and formally introduced the concept of the ‘limbic system’ (MacLean, 1996, Lambert, 2003). MacLean also developed the concept of the ‘triune brain,’ (MacLean, 1949) which is a great aid to understanding the neuro-sociophysiology of defence and PTSD. In recognition of the importance of MacLean’s research and ideas a special edition of Physiology and Behavior was recently devoted to him (Lambert and Gerlai, 2003).

MacLean’s triune brain concept (MacLean, 1949, MacLean 1990) suggested on both anatomical and functional grounds that forebrain structures evolved in three major eras – the early reptilian era (originating approximately 300 million years ago), the early mammalian era (200 million years ago) and the new mammalian era (originating 65 million years ago). Some features of PTSD are purely involuntary, e.g. the startle reflex, hence are likely to be activated by even older brain structures and have been located as emanating from the brain-stem (Koch, 1999). Understanding PTSD symptoms from this perspective may help not only research but also patients’ understanding and management of their bewildering symptoms.

MacLean’s theory has been criticised, but only in matters of detail (Cory, 2002). The main point is that there are at least three ‘central processing assemblies’ arranged rostrally/caudally in the forebrain, and that each assembly makes decisions relatively independently in dealing with changes in the environment. This is far from self-evident, and contrasts with the idea of a gradual and homogeneous accretion of brain

volume during evolution. It also reflects the remarkable fact that the neomammalian forebrain, which must be the most sophisticated adaptation in the whole of evolution, has very little control over the lower

two levels, resulting in the reality that we cannot simply will ourselves to feel less angry or less depressed.

Panksepp (2006) has recently emphasized the desirability of examining psychiatric disorders from the bottom-up by way of ‘endophenotypes,’ primal brain functions that can be linked to neural circuits and the underlying genetic controls. Endophenotypes may be similar to the ‘psychobiological response patterns’ of Gilbert (1992). We propose that appeasement is the most likely endophenotype for complex PTSD. Appeasement may operate at one or all three triune brain levels. In its most primitive form appeasement is an all-or-nothing response, as seen in contemporary reptiles. In a number of reptile species appeasement takes the form of total body colour change, in which an adult male will give up its bright coloring and revert to the dark muddy brown of immature animals (Greenberg & Crews, 1983). When a dominant-subordinate pair of Anolis carolinensis (lizards) is broken up, the subordinate’s color often becomes lighter again. Sometimes color change is irreversible reflecting pathological processes associated with status change. In such animals, color becomes progressively darker and the animals eventually die.

Thus this lizard cannot appease one rival while dominating another. This all-or-nothing characteristic of reptilian appeasement is one reason we allocate to the reptilian level of the forebrain the strategy selection between elevation and depression of mood, both of which are pervasive in their effects on behavior. To the extent that PTSD is associated with depressed mood, this acts as one component of the appeasement display.

The middle, or paleomammalian level of the triune brain involves the limbic system and emotional reactions. The subordinate rodent, canid or primate feels fear and a sense of being chastened by the dominant animal. We refer to this as depressed emotion, to distinguish it from depressed mood. The depressed emotion is not pervasive, but is context dependent, reflecting the fact that in a mammalian hierarchy most animals operate in the middle and while being chastened from above, they may be aggressive to those lower in rank and expect appeasement from them. They express anxiety looking up but irritability looking down the hierarchy. Also, since sanctions may be applied by the group as well as by individuals, they feel shame when not reaching the group’s standards, and guilt at breaching the group’s rules. Human blushing accompanies this paleomammalian appeasement display.

At the neomammalian level are the rational, voluntary, conscious adoption of appeasement, which may require considerable social skill, as in a flowery speech of submission. Moreover, appeasement at this level may be either genuine (accompanied by respect or affection for the dominant individual) or simulated, in which the individual goes through the motions of appeasement but has no genuine submissive feeling and may be planning a come-back or rebellion (a possibility which Milton, an expert in appeasement or the lack of it, has Satan consider, and reject, in the first book of Paradise Lost). Patty Hearst described during her captivity being orientated to deliberately doing whatever she had to (by way of appeasement) to survive, but found herself also led on by some appeasing force she did not understand (Hearst & Moscow, 1982). This would be compatible with triune levels of appeasement operating simultaneously.

Fear responses involving flight and aggressive defence/fight require rapid processing. Neomammalian cognitions permit complexity but are slow. The more primitive brain levels provide more rapid reactions (Le Doux, 1996, Panksepp, 1998). Bracha (2006) has even suggested specific evolutionary time-frames for the origins of the many fears humans experience – e.g. fears of heights, separation, darkness, snakes, drowning, etc.. Whether his time-frames are correct or not his suggestion that these fear subtypes have different origins is intriguing. PTSD may involve greater contributions from the reptilian and paleomammalian brain levels. Patients often report surprising difficulty implementing exposure programs. It is as if there is something unexplainable deterring the progress that otherwise logically seems readily attainable. However, the association of appeasement with complex socialization suggests appeasement in the great apes (including ourselves) is likely to have evolved with greater neomammalian selection pressures than the other defences (Cantor, 2005).

Appeasement may be associated with changes in the chemistry and anatomy of the brain. Work is currently being carried out on cynomolgous monkeys (Shively et al., 2006), tree shrews (Fuchs, 2005), rats (Nikulina, Miczek & Hammer, 2005), mice (Yapp, Covington, Gale, Datta & Miczek, 2005) and cichlid fish (Fernald, 2002).

Conclusions

The exploration of biological behavioral phenomena by cross species comparisons and the use of evolutionary theory has been relatively underutilized in mental health and particularly in PTSD research. A model of PTSD based on defence provides a plausible basis for biological research and clinical

practice. Our use of these principles suggests that the biological basis of complex PTSD is the specific defence, appeasement. As with many paradoxes phenomena including the Stockholm Syndrome and victims’ of domestic abuse idealization of the abuser become readily understandable when viewed from a new perspective. Evolutionary psychology in conjunction with the triune brain concept provides a basis for linking neuroscientific research with behavioral responses in particular contextual situations. Neurobiological, behavioral and social scientific research may be bridged and thereby united by such undestandings.

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