Bargaining Model of Suicidal Behavior
The bargaining model of suicidal behavior frames such acts as costly signals of need. The following conditions are necessary for the model to operate: (1) the victim encounters of a fitness threat in the environment prior to suicidal behavior; (2) there is a conflict of interest between the victim and invested social partners such that the social partners are not otherwise willing to provide support based on less costly signals alone (e.g., verbal communication); (3) the victim is otherwise powerless to remove the fitness threat on her own; (4) more often than not the victim survives the attempt; (5) the nonlethal suicide attempt communicates to social partners that she is truly in need; (6) the social partners assist the victim in removing the fitness threat.
Suicide is a universal human tragedy. According to the World Health Organization, suicide is the sources of more deaths than all wars and homicides combined (Lozano et al. 2013). In light of evolution, we know that all behaviors are either the functional output of psychological mechanisms, by-products of mechanisms that evolved for other reasons, or the product of dysfunctioning mechanisms, and suicidal behaviors (SB) are no exception. Mental health professionals and investigators tend to reasonably assume that SB is a consequence of one or more dysfunctions. However, theoretically and empirically, evolutionary scientists know that increasing fitness can come at the expense of survival such exhibited in the cases of semelparity or intrasexual combat. Considering the universality of suicidal behavior, some evolutionary researchers have investigated suicidal behavior in an evolutionary light. One popular model called the inclusive fitness model proposes that suicide death could have evolved to benefit genetic kin when the victim (1) has low reproductive potential and (2) is a burden on genetic relatives (e.g., de Catanzaro 1984). The inclusive fitness model concerns suicide death. However, humans have evolved physiological and psychological traits to prevent harm such as pain receptors and conditioned avoidance that are difficult to overcome. In fact, in the USA, most suicidal behavior is nonlethal (Syme et al. 2016). The bargaining model of suicidal behavior (BRM) concerns the evolved function of nonlethal suicide completions.
The BRM, formally developed by biological anthropologist Edward Hagen and tested by Syme et al. 2016, frames self-inflicted harm with intent to die as a costly signal of need. The following conditions are necessary for the model to operate: (1) the victim encounters of a fitness threat in the environment prior to suicidal behavior; (2) there is a conflict of interest between the victim and invested social partners such that the social partners are not otherwise willing to provide support based on less costly signals alone (e.g., verbal communication); (3) the victim is otherwise powerless to remove the fitness threat on her own; (4) more often than not the victim survives the attempt; (5) the nonlethal suicide attempt communicates to social partners that she is truly in need; (6) the social partners assist the victim in removing the fitness threat.
Conflicts of Interest, Costly Signaling, and Suicidal Behavior
Zahavi observed that human speech is a cheap form of communication that is unreliable when there is a conflict of interest between two parties and therefore an incentive for one to deceive (Zahavi 1993). Taking this view, the BRM suggests that we should predict suicidal behavior to place when there are high stakes conflicts of interest where parties cannot believe each other based on verbal communication alone.
Powerlessness, Fitness Threats, and Suicidal Behavior
According to the BRM, suicide attempts should outnumber suicide completions, and suicide attempts should be more common among those with high reproductive potential whose fitness is constrained but who are otherwise healthy. According to data from the Center for Disease Control, the rate of suicide attempts in young adults exceeds the rate of completions by factors of 10–100 or more, and this ratio diminishes with age (Syme et al. 2016).
In this framework, suicidal behavior is a last resort of the powerless. Farberow and Shneidman (1961) described suicide as a “cry for help.” Psychiatrist Erwin Stengel reported that suicide attempts often occurred in response to an intolerable social or emotional situation and were often nonlethal. Suicidal behavior is thus a plea entailing a gamble with death (e.g., Stengel 1956). The BRM pinpoints severe, fitness threats, such as physical or sexual abuse, as precursors that make this gamble with death worthwhile from the standpoint of natural selection. According to a WHO study, trauma exposure predicts subsequent suicidal ideation and attempts in a dose-dependent sequence (Stein et al. 2010).
Cross-Cultural Research on Suicidal Behavior
Ethnographic data from a range of unique cultures unambiguously demonstrates that SB can effectively communicate dissent and serve as a check on abuse and exploitation, and the BRM frames these protest themes of suicidality in game theoretic terms. For instance, Firth characterized acts of SB among the Tikopia as a form of protest, particularly for sons in conflict with domineering fathers (Firth 1936). In the Middle East, SB among women is often regarded as recourse against oppressive kin or restrictive social structures (e.g., Billaud 2012), and the anthropological literature abounds with comparable models (see Syme et al. 2016 for review).
Syme et al. (2016) tested the BRM and the inclusive fitness model against 53 distinct cultures from the probability sample of the Human Relations Area Files. In support of the BRM, most victims of SB were powerless (e.g., had little social influence), were in conflict with powerful social partners who were otherwise invested in them (e.g., parents, community leaders), had experienced some type of fitness threat (e.g., rape, physical abuse), and, if they survived, social partners often helped to remove the fitness threat (e.g., put a stop to an arranged marriage). There was comparatively weaker evidence for the inclusive fitness model, which possibly characterized a small fraction of cases in northern latitudes where the environment is harsh, and where the support of noncontributing community members can present a burden. However, these suicides often required the assistance of another, which presents a problem to the theory that suicide for the sake of inclusive fitness is an evolved mechanism.
The BRM conceptualizes SB as a means of communication. In the model’s framework, the functional goal of at least some SB is to credibly signal a desperate need for social support, while death is a by-product of the signal’s high cost. There are several lines of evidence that support this hypothesis. If the BRM is operating, then the function of SB is to obtain protection, and unrelenting abuse would trigger future SB. The cost of the signal, which in this case manifests in self-harm, guarantees to observers that the signal is honest, i.e., the victim of SB is experiencing a severe social threat for which she needs social aid.
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