Justice from an Interdisciplinary Perspective: The Impact of the Revolution in Human Sciences on Peace Research and International Relations

Peace and justice have been a preferred couple in theoretical writings – but what do we know about their empirical relationship? Insights from other disciplines suggest that humans are highly sensitive to violations of justice and that justice concerns permeate social relations. Neuroscientists have located the parts of the brain responsible for negative reactions to violation of claims for justice. Evolutionary biologists have identified rules of distribution and retribution not only in early human societies but among other socially living species as well. Psychologists have observed the emergence of a sense of justice in very early childhood, while behavioral economists have identified behavior of average persons in experiments that deviated significantly from the model of the “economic man” and could only be explained by a sense of justice. The chapter summarizes these findings and outlines their implications for peace research. It highlights the ambivalent nature of justice for social relations. Justice concerns can exacerbate conflicts between individuals and groups but justice can also provide standards for arriving at durable peaceful solutions to conflicts. Understanding these ambivalences and their repercussions for international and intrastate relations provides a promising path towards understanding conflict dynamics.

these findings and identifies implications for the study of war and peace between and within states.
In doing so, this chapter aims at escaping from the intellectual straightjacket imposed by the narrow and incomplete perspective of humans as selfish, materialistic utility-seekers and of methodological individualism. It starts from the assumption that humans are as much moral as they are selfish (Monroe et al. 2009), that they are as much emotional as they are rational, and that they are as much social-communal as they are individual.
Based on these assumptions, "justice", the time-honored moral concept of political theory since ancient times, is presented as a central issue in international relations. This proposition is not based on philosophical deliberations, but on insights from many academic disciplines, including "hard sciences". As I will show on the following pages, these insights converge on the empirically supported proposition that humans are endowed with what could be called in layperson's terms a "sense of justice" and that this disposition in the hard wiring of our brain has momentous political consequences not only at the individual, small group and intergroup level, but also in politics and international relations. In a nutshell, the presence or absence of perceived justice is a key factor that decides on war and peace.
There is no doubt that peace without justice contains tensions between those suffering from perceived unjust treatment and those responsible for such treatment, as those on the receiving end of injustice will develop the "justice motive" (Lerner 1977) to close the gap between their justice claim and its lack of fulfillment. These tensions may endanger the stability of peace: unjust peace has the negative connotation of being unsustainable. Just peace, by contrast, displays the extremely important attribute of continuity and permanence. This statement should not come as a surprise. Justice means in general that members of a given community obtain what they can justly claim ("suum cuique"). When this is the case, satisfaction with the status quo prevails and the respective social order enjoys legitimacy. There is no motivation for violent resistance in order to create basic change. Under these circumstances, peace is sustainable. 1

Losing the J-Theme: The Weight of Paradigmatic Hegemony
The pedigree of the philosophical debate on justice and the gravity of its conceptual assumptions about human destiny should have motivated intense empirical research, but there is amazingly little to be found. Inevitably, empirical researchers have uncovered interesting insights into the role of distributive conflicts and their resolution in the sustainability of peace agreements, on the role of non-recognition in conflicts within and among political communities, on the impact of transitional justice on post-civil war societies, and on the meaning of fair procedures for the acceptance of negotiation results-all subjects intimately related to the idea of justice (e.g., Albin 2001;Albin and Druckman 2008Druckman and Wagner 2017;Zartman 1997Zartman , 2008. But these insights have had only marginal influence on the great theoretical debates, if any at all, and they have not informed thinking on conflict and conflict resolution in international relations to the degree they deserve. As David Welch, a pioneer in thinking about justice in international relations (Welch 1993), has recently written, the reason is most probably paradigmatic hegemony (Welch 2014). This certainly begs the question how empirical research about politics could lose sight of one of the key subjects of the social sciences and humanities: the meaning of morality and ethics in human affairs. Morality, at the center of the academy for millennia while philosophers and theologians were at the helm, has receded into small niches of scientific interest in modern science-though we have to give the philosophers credit for helping to keep the topic alive until now. In the social sciences, it has been consigned to the margins. For Marxists and poststructuralist, late Nietzscheans, morality is an ideological superstructure concealing the material or ideational basis of society. Similarly, rationalists view moral arguments as instruments of a rhetorical strategy (Schimmelfennig 2001) for overcoming resistance to actors' material interests (while never asking the question how moral arguments could exert influence among interest-pursuing actors in the first place). The social-Darwinist inheritance of (utilitarian) rationalism is only inadequately papered over by the apparent liberty rationalists have to identify their actors' (theoretically also altruistic) "preferences" (e.g., Lake and Powell 1999;Snidal 2013). In almost every empirical study informed by a rationalist perspective, it is the material, egotistic interests of individuals or their groupings that drive behavior, and the connection to the "survival" doctrine of the social Darwinists in this approach is not hard to identify. This view is alive despite all accumulated evidence that the "justice motive" is different from "selfinterest" (Markovsky 2017, pp. 115 f.).
All these approaches (we can include realism and neo-realism because both rely on an anthropology that focuses on survival or the egotistic enhancement of power, or both) have the anthropological assumption of egotistic individualism in common. Motivations driving groupings (such as clans, city-states, feudal entities or states) are mere extensions of what drives individuals. It is very hard to see a logical way morality could emerge from these basic assumptions about how humans are structured. As stated above, to treat morality instrumentally begs the question how it could be an instrument of persuasion for a group of egoists. This question remains unanswered.
Constructivists, by contrast, view ideational motivation as a permanent part of human dispositions and behavior. They postulate great variance in the substantive structure of these dispositions, as they are rooted in cultures which are historically path-dependent and thus vastly different when, say, the culture of a South East Asian society is compared with that of a sub-Saharan African or a Scandinavian one. There is little or no connection with the "hard science" basis of these assumptions. Constructivists rely on the tradition of social sciences and social philosophy. For quite some time now, this has been a disadvantage vis-àvis rationalism connected to evolutionary biology (though in the highly doubtful version of social Darwinism), with rationalism thus enjoying a more respectable "scientific" reputation (Jackson 2010).

The Key Role of Unproven Anthropological Assumptions
The hegemonic social science paradigm that has informed much of IR work is thus rationalism (Lake and Powell 1999). Humans are rational utility-seekers and maximizers or optimizers. Realism and neo-realism are variations of this basic theme. Structures emerge out of the strategic interaction of actors with different preferences which are frequently in opposition to each other. Structures then determine the strategic choices of actors; depending on the choices made, outcomes ensue and, from time to time, new preferences and structures emerge. Rationality may be limited through lack of information, and information exchange may become part of the strategic interaction among actors. Actors-whether natural persons or collectives-must be regarded as "individuals" who are only kept together by virtue of their strategic interaction and the resulting structures. I am not interested here in the fine-tuning of the whole theory and its application in IR, but in the skeleton of the anthropological assumptions that constitute their basis. As is well known, this very special anthropology has been imported from the academic field of economics. It should be emphasized that economics has adopted this anthropology without any preceding empirical anthropological studies. The founders of modern economics derived their conclusions from their lay observation of everyday behavior and expanded their conclusions to a simple if not primitive theory of how human beings "tick". When Charles Darwin laid the groundwork for evolutionary biology, pundits of utilitarian political economy were quick to jump on the bandwagon; lacking their own foundation in the hard sciences, here they found what they needed to bolster the "scientific" claim of their field. The struggle for survival of the fittest and the perceived "betterment"-in both physical and intellectual capacities-through the historical process of organic evolution appeared to support what economists viewed as the emulation of the biological template in the market system and the resulting betterment of human affairs resulting from ever more efficient production and distribution modes.
IR scholars of the realist and rationalist faith then followed this example, claiming, like the economists, scientific status based on the noble "hard science" pedigree behind the paradigm adopted. While rationalists focused closely on the micro-level, realists looked at the big picture (most notably Waltz 1979). In extremis, they described world history as a merciless fight for survival in which states had no other choice than to arm, to ally, and to fight, in order to survive. This sophisticated social Darwinism found its most consistent expression in "offensive realism" (Mearsheimer 2001). Never mind that the extinction rate in the world of states is surprisingly small, that many states focus on things other than survival, since they survive anyway, and that even extinct states may experience surprising resurrections-something highly unusual in the biological world other than through Jurassic Park techniques, which still belong in the realm of fiction.
The anthropological assumptions of rationalism have experienced many attacks, in the most sustained way by constructivists who wanted to leave the materialist ground on which rationalism is ultimately based and to give the ideational factors inherent in the human brain and in the social life of humans their due. But even constructivist work has succumbed at times to key elements of the rationalist paradigm, such as the evolutionary theory of norms (Florini 1996) or the utilitarian motivation of political leaders in John Owen's theory of forced regime change (Owen 2010). In many ways, rationalism offered the anthropological default option to which even critics of rationalism would revert when necessary. The reason was most probably the aura of "being scientific" resulting from the rationalist basis in economics (allegedly the most "scientific" social science, despite the endless sequence of incorrect prognoses), which in turn was rooted in an oversimplified and misunderstood interpretation of Darwinist evolutionary biology (Jackson 2010). Two images prevailed: "economic man" (Ingram 1888) and the "selfish gene" (Dawkins 1976).
Of course, any political theory must rely on basic anthropological assumptions. Without such assumptions, there can be no hypothesis about the motives and directions of human action, individual or collective. In modernity, these assumptions have been gathered in a rather amateurish, ad-hoc way, and they reflect the beliefs of academics to a far greater degree than any hard knowledge, from Morgenthau's "lust for power" (Morgenthau 1968) through Waltz's concern for security, to the prevailing rationalist paradigm of utility-maximization. In the past, political analysts could be excused by pointing to the vast discrepancy between existing "hard" knowledge and the ad-hoc assumptions related to the presently most plausible relevant "hard knowledge" to which they clung, namely evolutionary biology as understood by social scientists. 2 The time for such excuses has passed as a result of scientific advances over the last few decades. For the first time since the academic faculties split as a consequence of scientific development in the era of the Enlightenment, we may be facing a period of convergence for a wide range of academic fields from hard sciences such as neuroscience or evolutionary biology to sociology and political science (international relations included) and cultural sciences such as ethnology or literature. A chorus of jubilation could be expected over the immense opportunities this development is creating, over new, vast domains of academic possibilities opening before our eyes. It is a kind of underselling to speak only of an "emotional turn", which would be another temporary fashion for marketing a limited new idea imported from elsewhere (Hutchison and Bleiker 2014, p. 492). What is happening here is nothing less than a revolution across the field, based on a new and scientifically-based image of the human species and its motivational dispositions (Crawford 2011). Despite this, most scholars stick to their old models, from rational choice to post-structuralism, and neglect the marvelous chance of enriching our knowledge. 3 No social or political theory whose assumptions about human beings do not pass three crucial tests is sustainable nowadays. First, theories must be plausible in the light of evolutionary requirements: All attributes ascribed to human beings by social and political scientists must have a plausible evolutionary history in the human species, a history during which individuals have always been embedded in groups rather than being lone wolves. The attributes must be supported by at least some empirical evidence in evolutionary biology and anthropology (Hatemi and McDermott 2011b). Second, they must not contradict recent insights by neuroscience and neurobiology. These sciences, though quite young, are deciphering the structure and functions of the brain at astonishing speed, making use of rapidly developing new technologies. Third, they must find some support in the rapidly growing body of experimental research in sociology, social psychology and behavioral economics.

Insights on the Justice Motive from Many Disciplines
Trying to distill the knowledge from various scientific fields with a view to obtaining answers to key questions is akin to a fool's errand: too many possible sources in too many unknown fields, and too much specialist knowledge needed to understand what these far-away colleagues are writing. The best an interested layperson can do is to start with the few scientific authors who care (and are capable) of presenting their field to a broader, interested audience, and to work through their key references to touch upon a wider circle of writings. This is what I have done in preparing this chapter.

The Justice-Seeking Human as Social Animal: Insights from Evolutionary Biology and Anthropology
There is no way to understand political motivation, choices, and sociality without a deep look at the evolutionary history of the human species. Evolution has led to the emergence of key universal traits underlying preferences and influencing political attitudes and decisions which work through the structure of the brain (see below) and the central and peripheral nervous systems. Moreover, traits transferred by individual's genetic inheritance show considerable variability; some individual differences in political orientation and reaction to specific environments are probably inherited: "Individuals with different traits may respond differently to the same trigger, just as individuals with the same trait may respond similarly to different cures [sic!]. In essence, part of an individual's trait may include inclinations how to best interpret the environment; some individuals will see threat where others see opportunity" (Hatemi and McDermott 2011a, p. 25). To understand political behavior in general, knowledge of the universals is essential. To understand single cases of decision making at the microlevel, recognizing individual differences is necessary. I am interested here in the big picture, and thus focus on the universal characteristics of human sociality. Human beings, compared with all other species, need an extraordinarily long development period to grow up to a degree where they are capable of surviving on their own. For one and a half decades they are relatively helpless and need protection and provision of food and other necessities by adult persons. Not only their bodily competencies need this long period of childhood and adolescence to achieve full strength, their brain also needs this long period for full development and, in addition, for mastering the content of cultural knowledge for coping with the challenges of life, which is the outstanding characteristic of our species.
To survive this long "under-age" period of life, humans must be embedded in groups (of variable size, see below) which care for them. This necessitates certain attributes in our "genetic hard wiring" which we do not share with all species on earth, nor with all vertebrates or mammals, but only with those which, like us, live in groups whose social coherence provides the necessary environment for survival. This social embedding may include the possibility of being adopted if a child's natural parents die very early, or of being cared for in the case of handicaps, injuries, illness and the disabilities connected with old age. All these possibilities have been shown to have existed in early human society and exist in great-ape groups (de Waal 2015, pp. 69, 83). In other words, apart from the capability of surviving as individuals (which humans must do-like any other species-in order to deliver their genes to the next generation), humans need the capability to help their group survive and to function in a surviving group, in order to master life individually and as a species through the course of evolution. Behavioral traits (and their biophysical substrate) that foster group cohesion and strength are a condition for evolutionary success of any social species (more below). Brian Skyrms has shown in a series of evolutionary game simulations that cooperative traits related to fairness/justice beat selfishness in the "competition for fitness" (Skyrms 2014).
If this assumption holds true, we should find behavioral regularities selected by the necessity of functioning in a group and making the group function in non-human species which are also "social". Most prominently, we should find similarities with our closest relatives, the great apes, and these similarities should even extend to attributes of the brain, as far as it has been already deciphered.
Evolutionary biologists (Bekoff andPierce 2009), primate researchers (de Waal 2009;Yamamoto and Takimoto 2012) and anthropologists (Boehm 2001) have explained the competitive advantages of species living in social communities which result from fairness rules concerning distribution of food, punishment for unruly behavior (Brosnan and de Waal 2012), and accepted rules for making decisions in the group, whether they are more hierarchical or more egalitarian. Such rules (from simple to complex) were found in an astonishing array of social species ranging from cleaner fish through coyotes, wolves and crows (Bekoff and Pierce 2009) to our closest relatives, the primates, notably the great apes, and finally to early human societies (Boehm 2001).
Among the great apes, chimpanzees and bonobos are our cousins. We share a common ancestor, and we share certain traits in behavioral patterns and brain structure with both, even though the two species are different. Chimpanzees live in patriarchal societies, are strictly hierarchical, relatively competitive and violent (but with rules) internally, and strongly violent towards other groups of the same species. Bonobos live in slightly matriarchal societies, are more inclined to solve internal conflict non-violently (with the aid of frequent sexual intercourse in the service of conflict management and resolution) and, while careful to protect territorial borders, are inclined to fraternize with bonobo outgroups rather than make war on them (de Waal 2015, pp. 24 f., 92 ff.).
As de Waal observes, these great apes, like humans, strive for power, security, and affection from others, love sex, defend their territory, and appreciate trust and cooperation (de Waal 2015, p. 29). We also find elements of a sense of justice/fairness in these species. It starts with "inequity aversion", the disinclination to tolerate unfair (unequal) treatment in distribution situations (de Waal 2015, pp. 30 f.). It appears that we share with the chimpanzee a disposition to strong intragroup competitiveness, balanced by the striving for intragroup cooperation, and with the bonobos a very strong disposition to empathy, based on the VEN neuron type, which both we and they possess (de Waal 2015, pp. 112 ff.). 4 Chimpanzees and bonobos both display clear behavioral patterns concerning food distribution (de Waal 2015, p. 170). Chimpanzees principally share meat gained from hunting. Successful hunting is followed by loud calls from the hunters, signaling the imminent feast. Concerning "vegetarian food" (fruits, leaves, branches), by contrast, the possessor of the food distributes it. However, other group members-even alpha individuals-start begging, and usually the possessor will hand over part of the food to other group members. 5 Approaching special places where food is located (e.g., in captivity), the social hierarchy decides on the sequence in which individuals are admitted to the source. In bonobo societies, female individuals, according to their rank order, approach first. Even leading males come later (de Waal 2015, pp. 108 f., 175 f., 260).
Implementation of justice is also an important element for reducing the degree of (violent) conflict in a group. In chimpanzee and bonobo societies, older individuals (not necessarily the actual alpha members) act as arbiters in intragroup conflicts-notably conflicts where violence is actually used or threatened to be used-and excel by their complete impartiality (if friends or close relatives are involved, they are not favored) (de Waal 2015, pp. 34 f., 67 f.).
Altogether, in the world of primates we find the characteristic ambivalence which we know from human society: The social world is a world of competition (which can become very tough and cruel), but on the other hand it is also an environment with traits of community, where norms of appropriateness apply, sympathy and help from others can be expected, and isolation and loneliness of the individual is a deviant-pathological-situation (de Waal 2015, p. 43; Proctor and Brosnan 2011). 5 As an amateur bonobo observer, stimulated by de Waal's imposing studies, I regularly watch the quite sizable bonobo community in the Frankfurt Zoo. Two recent observations confirm de Waal's propositions: In the first episode, a very young individual, sitting close to his/her mother, was holding and eating a banana. An older, very senior female (possibly the alpha) approached and showed her interest in eating the banana. Rather than taking it, it started begging the little one for a piece. The baby reacted in the cutest possible way. It took a bite and transferred it with a kiss into the mouth of the senior. She kissed back and all three apes smiled at each other. In the second episode, an older female was holding a branch with apparently quite delicate leaves. When she let go of it for a moment an adolescent male jumped from a tree stealing the branch. The female shouted and pursued the perpetrator. Even when he let go of the branch she pursued him, caught him and hit him several times but without inflicting wounds. The mother of the adolescent watched the scene without any reaction. The adolescent sat in a corner, not even approaching his mother for consolation. In the first episode, food distribution rules were observed by all three participants, even the very young one (and how charmingly!). In the second episode, the rules were violated, and retributive justice followed. The mother did not interfere, thus putting the rules before kinship. And even the perpetrator showed what could be interpreted as signs of remorse in the end.
Many primates, not only our closest cousins, share the capability to cooperate, a strong aversion against inequality, a concern for status (recognition), and an inclination to observe social rules (for a hierarchical order of status, food distribution, reciprocity and alliance building) that helps mitigate the possibly devastating consequences of status competition and inequality aversion within social groups (Proctor and Brosnan 2011).
Looking at more recent work in the field of anthropology, we find strong parallels of early human social life to primate societies. Charles Boehm described in great detail the development of food-sharing rules and how the ambitions of very strong individuals have been tamed by the emergence of egalitarian practices and norms in human hunter-gatherer societies (Boehm 2001). He also demonstrated that deviant behavior has been punished by shaming, blaming and temporal isolation, while persistent deviants who threaten the integrity of the group have suffered expulsion or even the death penalty (Boehm 2001(Boehm , 2012. What applies to primates from an evolutionary perspective applies to early human society as well: in addition to the individual capability to survive, the group's capability to survive is decisive for successful evolutionary development, as the group, in turn, is the necessary condition for the individual's survival. Group survival depends on viable and predictable relationships within the group, where competition, cooperation and mutual care must be balanced. The balance ultimately hinges on valid rules of justice/fairness based on mutual recognition, reciprocity, practices of sharing and care, and punishment of inappropriate behavior. All these norms and practices are instantiations of the principle of "suum cuique", which appears to be interculturally accepted as the highest and most general principle of justice, whereas the specific substance of "suum" and "cui" varies considerably within and between cultures. 6 But the existence of such rules removes many conflict triggers from society as it combines a shared sense of "appropriateness" with the feeling that individuals, independently of their particular status in the group, will get their due, that deviations from the norms will be corrected, and that wrongdoers will be punished. Justice, order, and group coherence are thus intimately connected (de Waal 2015, p. 304 ff.).
These aspects of justice in societal species are likely to relate to four evolutionary functions: First, to keep the largest number of group members alive in order to have a "reserve of individuals" in hard times and, more immediately, to be capable of resisting attacks by predators from other species or by rival groups of the same species in the competition for the territory in which the group lives. Rules for sharing food are essential. It has to be emphasized that this does not necessarily mean equal sharing. In many social species, alpha individuals eat first and obtain the best pieces of food, yet weaker individuals are not denied. The sharing function serves to prevent group members from starving and to provide enough food for next-generation group members to grow successfully. Caring for children as a collective task (Hrdy 2010) including, just in case, the practice of adoption as mentioned above, serves the same general function, which deviates from the templates of both utilitarian egotism of the individual and of the "selfish gene". Christopher Boehm also argues that food sharing (notably applying to meat, with its significant protein supply) evens out survival conditions among group members between the strongest and the weakest. He also notes that sharing extends beyond the narrow kinship group and includes non-relatives in the band (Boehm 2001, pp. 184 ff.). All this, he emphasizes, favors more altruistic groups in interband competition (Boehm 2001, pp. 218 ff.).
Second, keeping the group effective (decision-making). Social animals have and early human societies had distinct rules concerning how to make decisions. Primate societies are hierarchical in various ways, but it appears that it would be too easy to ascribe decision-making power only to the chimpanzee or bonobo alpha animal. Rather, primate researchers observe various coalitions on which even alphas have to rely. Human hunter and gatherer societies as well as agriculture-based tribal societies are more egalitarian. Boehm argues that apart from the "lust for power", which he sees as a natural trait in (mostly male) humans, and the readiness to (reluctantly) submit to a superior "alpha" in order to avoid harm, there is the equally strong desire to preserve the individual's autonomy against others' aspiration for dominance (Boehm 2001, pp. 67, 163 f.). Using a broad spectrum of historical and ethnographic evidence, he maintains that these societies have found ways of neutralizing this aspiration, and have helped nature in favoring the selection of the genes of more altruistic and empathic individuals by treating strongly deviant "big egos" through ostracism or even execution (Boehm 2001, pp. 27 f.). Human hunter and gatherer societies are more egalitarian; the development of hunting tools for killing game produced an equalizing effect of "political" rivalry comparable to a pre-weapon competition based on the individuals' raw physical strength (Boehm 2001, pp. 180 f.). Decisions are mostly discussed among the (adult male) members of the group/band and require consensus in the group. These modes, internalized by group members, have proven effective enough to permit the group to survive.
Third, enforcing rules (punishment). The emotions which accompany the positive experience of being treated justly and the negative emotions connected with perceived unfairness serve important functions both for the individual and for the group. They help the individual get what he/she needs for survival and they help the group to stick together and maintain the bonds needed for the collaboration that is essential for survival (Keltner et al. 2006). Retributive justice (Wenzel and Okimoto 2016) is observable across social vertebrate species (Proctor and Brosnan 2011, pp. 55 f.). Punishment follows the inappropriate application of force, for example when young wolves, coyotes or dogs are punished for a disproportionately sharp bite during play, or when chimpanzees or bonobos hurt another group member severely in a rivalry or sex competition situation, or when a group member appropriates food to which another member had a justified claim (de Waal 2015, p. 219; for findings concerning canids, cf. Bekoff 2001). Even superior group members (alphas) may suffer punishment in such situations (de Waal 2015, pp. 215 f., 219 f.). De Waal reports an episode in a bonobo group where a high-status male, by approaching a female in whom he was interested was terrifying her baby and thus endangering it. The event led to one of the very few instances of violence in the group, with highly emotionalized members ganging up against the perpetrator because of his "crime" (de Waal 2015, pp. 109 f.).
Punishment may range from vocal disapproval through minor physical retribution to the ultimate horror punishment, expulsion from the group. Isolation from the community can cause death in the wilderness. Individuals in social species are primed to avoid this fate: The human brain, for example, reacts very strongly to experiences of isolation. Lack of success in intimate relations, or their breakdown, or the loss of a very close individual creates stress and anxiety. In extremis, the whole motivational system may collapse or may focus on aggression as a means of gaining recognition and group membership (Bauer 2010, pp. 39 f., 63 ff., 75 ff.). This explains the key role of "recognition justice", the claim to be accepted as a worthy member of the club, in the order of human justice claims as priority "suum cuique". It also helps understand the devastating psychological impact of successful mobbing activities in modern social interactions.
Charles Boehm documents punishment practices against (powerful) deviants on a very broad empirical basis (Boehm 2001, Chaps. 3 and 4). He assumes that in hunter/gatherer societies, deadly punishment of violent and psychopathic deviators has shifted the human gene pool towards the more altruistic, moral and cooperative side (Boehm 2012), an effect he also ascribes to intergroup competition/selection, in which groups with strong coherence (based on altruism and justice/fairness rules) fare better than their competitors composed of egoists (Boehm 2001, Chap. 9). At any rate, punishment of inappropriateness has certainly served another important function, namely preservation of the coherence of the group.
Fourth, keeping the group together. This is no trivial task given the inevitable and in many regards functionally beneficial role of intragroup competition and conflict. These centrifugal forces had to be kept in check in order to preserve group cohesion as the key to both group and individual survival when facing three challenges: The first challenge emanated from predators which could jeopardize the survival of the group in the early phase of human evolution.
The second challenge was the occasional encounter between different human groups which could result in violent and deadly competition (Boehm 2001, pp. 158 f.). The evolutionary "genetic response" is very clearly reflected in the finding of De Dreu and others that the production of oxytocin-one of the messenger substances triggering feelings of wellbeing and happiness-in the human brain is activated more frequently when mutual trust and close collaboration in a group is reaffirmed while the group is confronted with a rival or hostile outgroup (De Dreu et al. 2010). Mutual trust is a result of being treated fairly in your own group. On the one hand, the oxytocin level rises as a result of such experiences and, on the other hand, they enhance mutual trust (Bauer 2010, p. 47).
The third challenge is the "stag hunt" temptation in joint hunting. "Stag hunt" is a paradigmatic game theory construction in which individuals of a hunting band are tempted to desert the common project of hunting a stag for the easier prey for the deviating individual of a hare. Of course, humans would hunt the hare if they were completely egotistic utilitarians and the group would break apart. That hunter/gatherer bands survived the stag hunt trap for 150,000 years shows that humans, through genetic disposition, socialization and maintenance of rules, were capable of resisting this temptation.
In response to all three challenges we see dispositions which favor support for the common good over individual utility. These altruistic/communal dispositions underlie a sense of duty that is offset by a consciousness of rights (e.g., in food sharing). The balance of duties and rights represents, of course, a central aspect of justice/fairness. Reciprocity is another justice-related behavioral pattern which human society shares with primate societies. Primate reciprocity appears in food sharing and grooming: favors are acknowledged by returning favors, often with considerable temporal delay (de Waal 2015, pp. 175 f.). The most basic rules we are inclined to observe (most of us most of the time) and which shape the way justice/fairness is internalized genetically and culturally in primate and human groups, and which, from early human society on, have become institutionalized, are reciprocity, impartiality of arbitration, rules of sharing, and rules of participation (de Waal 2015, p. 49;Boehm 2001Boehm , 2012. The length of primate evolutionary history including pre-human forms is estimated to be 6 million years. Proto-human and human evolutionary history encompasses between 1.8 and 2.8 million years, long enough for selecting a genetic disposition adapted to group life, at a time when dispersed small groups living at considerable distance from each other had to reproduce by incestuous practices. This inbreeding created the conditions for the relatively rapid selection of intergroup differences in genetic dispositions. Even the gathering/hunting group/band stage of at least 150,000 years could be enough to establish relevant social dispositions in the human brain (Boehm 2001). It is not necessary for the whole population to have a strong prosocial disposition: Evolutionary simulation games have found that groups are adaptive with a mix of members of altruists, "punishers" (keen to avenge breaches of the rules), egotists and (isolationist) rulers, as long as the first two types are prevalent (Fowler et al. 2011, p. 210).

The Justice Disposition in Our Brain: What Can We
Learn from Neuroscience?
Neuroscience/neurobiology is among the most dynamic scientific fields (for an introduction see Damasio 2005). Progress is amazing. Some of the more relevant findings relate to the subject matter of this chapter. 7 Key emotions have no single center in the brain (which was an early hypothesis), but emerge from the "cooperation" of several regions which can communicate neuronally or biochemically (for a survey of the roles of different parts of the brain see Schreiber 2011). Biochemical connection means that regions in the brain trigger the flux of biochemical "messenger" substances (e.g., hormones) which, in turn, cause positive or negative feelings (e.g., joy, frustration, aggression or disgust). What we may call the "sense of fairness" (or justice) for want of a better expression is one of these structures of cooperation (Nam et al. 2017). As de Waal remarks, the mere fact that humans care about justice would not be there if a disposition to do so were not anchored in their genetic hard wiring (de Waal 2015, p. 44).
Being justly treated, in other words obtaining what people believe they are entitled to, or simply receiving the recognition they desire (and need) are among the experiences-all connected to positive relations to other human beingswhich trigger the production and transmission of the messenger substances (namely dopamine, endorphin, encephalin and oxytocin) that cause feelings of desire, happiness, sympathy, warmth, and so on. Experiences of being treated unjustly, of being denied what is due or being treated with contempt instead of respect cause feelings of resentment, aggression or even physical nausea ( Henrich et al. 2001;Singer 2007;Pinker 2011, p. 858). Experiments have also found that the perception of unfairness triggers strong emotions and willingness of the person concerned to strike back against the perceived source of unfair treatment (Svirastava et al. 2009). These findings help to understand the everyday experience that both the satisfaction of being treated justly as well as the frustration of suffering perceived injustice are connected to strong emotions, in the latter case stimulating even violent reactions (Mercer 2010). Pinker describes in great detail how the "wrath system" which we share with our vertebrate relatives follows registration of the experience of frustration or threat, and triggers defensive or offensive aggressive reactions. He also shows how this system is connected to a distinct second aggression-stimulating structure in the brain that is activated in competitive constellations and uses testosterone as the messenger substance. If the fighting escalates, the strategic use of violence degenerates into violence guided by blind wrath (Pinker 2011, pp. 736 ff.). Since the competitive disposition relates to the individual's status and hence to the recognition dimension of justice, it is another path through which justice concerns may lead to the readiness to apply violence (see also Mercer 2010).
Neuroplastics, one of the branches of neuroscience, investigates how not only neuronal connections but also certain aspects of the brain's biochemistry are completed only after birth and as a result of experiences in early childhood (Davidson et al. 2000). From this research, it appears that the genetic dispositions which brain researchers have now located need a kind of interactive development in which the young brain requires positive stimulus from an empathic and loving environment to grow to full potential, not only in its cognitive and reflective but also in its emotive, moral and social capacities. Early feelings of being cared for (the equivalent of feelings of "recognition") contribute to the capability to produce and trigger the flow of messenger substances which cause "good feelings" of happiness. Equally, the capability to develop empathy with others also appears to depend on the experience of being treated with empathy. Individuals who do not have these positive experiences in early childhood appear to develop deficits in this regard (Bauer 2004(Bauer , 2010 for an excellent overview see Druckman 2008).
What is intriguing is the close connection between fairness/justice and "recognition", and the key role this complex plays in switching the human mind between happiness and readiness to enter into conflict. Nancy Fraser has postulated recognition as the third type of human justice concern, apart from distributive and participative concerns (Fraser 2008). Axel Honneth puts recognition, or lack thereof, at the root of social and political conflict (Honneth 2010). From an IR perspective, Reinhard Wolf (2017) has emphasized the striving for respect shown by governments of all kinds and the negative reactions once such respect is denied. These deliberations are seen to be accurate in the light of what we can learn from neurobiologists and development psychologists, as is Ned Lebow's insistence that the "spirit" (which can be understood as the need for recognition) is responsible for most conflicts between human collectivities (Lebow 2008(Lebow , 2010. 8 As Joachim Bauer and other authors show, the motivational system of the human brain is programmed to strive for close relations with other people and with the group in which individuals live and where their identity is deeply rooted (Insel and Fernald 2004;Bauer 2010). People lacking this form of intense bonding frequently display psychological deviance. These insights should not come as a surprise, because humans can only survive when they are embedded in social groups, and the ability to achieve this condition for survival requires robust dispositions in human genes. As neuroscientists tell us, precisely these dispositions exist. The desire for justice, and the positive and negative reactions depending on whether the individual is treated justly or not, is an important element of these dispositions, because just treatment confirms that group membership is a condition of the individual's life.
From my readings, I would speculate that the justice aspect of recognition is not just a part of the whole complex that connects justice issues to emotions, but the most fundamental element because of-as argued in the previous sectionthe central importance of being accepted by the group for individuals to survive. I hypothesize that the recognition issue is also the element that drives emotions in the realms of distribution and participatory justice. Being afforded what ( people believe) is their due signals recognition of the individual by the person or the group or the system that manages the distribution of the good in question. To be involved as a participant in decision making also signals recognition of the person as being entitled to play a meaningful role in the group. All these are essential aspects of the individual-group relationship, in which the individual has the greatest stake, and toward which he/she is hard wired to strive, which is a major component of our emotive and cognitive apparatus (see also Dutton 2006).
The relation between the sense of fairness/justice and empathy appears to be of particular importance: empathy is the basis of the capability to have active feelings of alter-justice, that is, to empathize with positive or negative justice experiences of other people (Mathur et al. 2010). 9 The capability for empathy rests most fundamentally in a specific type of neuron in our brain, the mirror neurons. It enables us to quasi-simulate in ourselves what we observe another human or animal doing, experiencing, enjoying or suffering (our capacity to imitate is also derived from these neurons) (Bauer 2005;de Waal 2015, pp. 182 ff.). Measurements of brain activity have shown that in experiments people react positively to satisfaction of the justice concerns of others and negatively to frustration of their justice concerns. Comparisons show that these empathic brain activities are somehow weaker than those occurring in connection with the individual's own concerns, but are still clearly measurable. The same asymmetry has been found between the strength of empathy towards ingroup members as compared with members of an outgroup (Nam et al. 2017, p. 293;Hein et al. 2016;Cikara et al. 2012).
If the neuroscientists tell us about our disposition to be motivated by justice and to react to its manifestations, developmental psychologists show how these dispositions are activated and develop in very young humans. Notably Michael Tomasello's work on early childhood has shown that empathy emerges very early in life, and that the first indications of a sense of justice manifest themselves in some individuals as early as 18 months. Make no mistake: children can be egotistical, but all the same they recognize rules of reciprocity and of sharing and show emotions in connection with satisfied and frustrated claims not only by themselves but by their peers as well. Children of four to five years, left playing without supervision, have been observed adopting third-person justice perspectives by prompting peers to share toys fairly with other children (Arsenio and Killen 1996). The research by developmental psychologists appears to imply that the dispositions that enable us to feel a "sense of justice" are activated early in and through social relations, and develop over the whole of childhood and adolescence (Tomasello 2009).
Combining the findings of the two sciences, neuroscience and developmental psychology, suggests that our morality, to which a "sense of justice" is central, has a biological basis which unfolds its potential in interactions with the humansocial environment. The double evidence annihilates the notion of humans as cold and calculating utilitarian egotists. Of course this attitude exists and is also an expression of a disposition based in our "hard wiring". But it is only part of the whole (see below). To confuse this part with the entirety of human dispositions leads to deficient anthropological assumptions and, as a corollary, misinformed social and political theory.

The Death of "Economic Man": Evidence from Recent Work in Sociology, Behavioral Economics, and Neuroeconomics
Sociologists (Liebig and Lengfeld 2002) and experimental economists (Loewenstein et al. 1989;Fehr and Schmidt 1999) have verified in many experiments that people in games simulating distributive conflict and dilemmas deviate from the model of utility-maximizing behavior in favor of rules of fair distribution. Sociologists and social psychologists have proven that such justice concerns apply to the individual as well as to collectives. These collectives can be small, such as the family or a peer group, mid-sized like a university, a city, or a soccer club, or may be large, such as a nation, an alliance, an ethnicity or a religion. Grouping frames can be structural and enduring, such as the groups just mentioned, or ad hoc and short-lived such as an experimental group put together by a social scientist. Even in these artificial groupings whose constructed character is known to all participants, the psychological, neuronal, and biochemical processes run with the same seriousness as in "real life" in the direction of we-feeling and empathy within the ingroup and the feeling of difference and distance towards outgroups (Pinker 2011, p. 773). Social groups develop rules for dealing with justice issues among their members which instantiate justice principles. Sociological justice research has identified the intracultural as well as intercultural diversity of these justice principles. This aspect is of particular relevance for the analysis of conflicts that emerge from conflicting justice principles postulated by different actors, and from the different application of the same principle to specific situations (Kals and Maes 2012 document the breadth of this research).
Sociologists have also found that one of the most popular philosophical solutions to the justice problem, John Rawls's Difference Principle is not supported by real world people's attitudes. Rawls's Difference Principle permits diverging from strict equality "so long as the inequalities in question would make the least advantaged in society materially better off than they would be under strict equality" (Lamont and Favor 2017). Rawls postulated that inequality is legitimate only to the degree that it fosters disproportionate gains for the poorest. The most popular idea about justice as revealed in polls is a combination of the justice principle of need (people should be granted the basics for their existence) and the justice principle of merit (individuals contributing to the common good should obtain a share proportional to their contribution) (Frohlich et al. 1987;Frohlich and Oppenheimer 1992;Frohlich 2007).
This combination is indicative of a certain flexibility of individuals in adhering to several justice principles. They may combine them, but they may also switch between them, depending on which one is more favorable for themselves or for their ingroup in a given situation. This opportunism of choice appears to be less a matter of conscious strategic choice in a selfish-utilitarian frame than of an intuitive, pre-cognitive decision which receives justification only after it has been taken, and it does not negate the existence of an inherent "sense of fairness" which is at the root of even this selfish version of justice behavior as well as of more altruistic phenomena (Valdesolo and DeSteno 2008). The psychological phenomenon called "self-serving bias" is common (Trivers 2011).
In experimental (behavioral) economics, the paradigmatic test for a "sense of fairness" is the ultimatum game (Fehr and Schmidt 1999): A finite number of chips or coins, say, ten, is given to a player who has to offer a share to a second player. If the partner accepts it, this distribution is implemented, and each player keeps the money that the distribution leads to. If the second player refuses, neither of the players receives a reward. According to economic rationality, the second player should accept any distribution which brings a gain greater than zero, and the first player should not offer more than the smallest possible sum. In fact, second players refuse-emotionally-what they regard as "unfair" offers ( usually offers below a third of the sum available). Most of the time first players offer forty to fifty percent. This means that not only do second players betray a selfrelated sense of appropriate fairness, but first players either anticipate that second players will act according to a fairness norm or are acting out of their own feeling that a fair offer is appropriate. The ultimatum game findings held up across cultures in a major comparative study featuring societies from Latin America, Papua New Guinea, Mongolia and Africa. At the same time, cultural and market structure differences contribute to considerable variation in behavioral detail (Henrich et al. 2004).
Since the original findings were published, the rapidly growing field of experimental/behavioral economics and neuro-economics has buried "economic man" for good. Cooperative impulses, internalized norms of fairness with a strong root in reciprocity, empathy, and, above all, the embedding in social groups contradict the orthodox idea of unfettered utilitarian individualism, and deviate significantly from neoliberal and neoclassical orthodoxy (Gintis et al. 2005). The entire range of motives on the basis of which humans act presents an amalgam of selfish and altruistic, rational-strategic and emotional drivers for economic and political choices and a considerable influence of the cultural and institutional environment, including the incentives it offers to actors (cf. Glimcher and Fehr 2013;Haidt 2007).
We are accustomed to thinking of politics, notably high politics related to conflicts of interest, peace and war, as distinct from ethical and moral considerations to which justice issues belong. We are equally accustomed under rationalist hegemony to think of this realm as the fiefdom of cool strategic calculation, remote from emotions. But if the sense of justice is part of both our genetic and our cultural inheritance (de Waal 2015, p. 63;Haidt 2007;Lamont and Favor 2017), then from the very beginning it has been implausible that politics, as a central area of human activity, could be isolated from its influence. In the end, this is an empirical question, and the findings, as far as they exist, point in the direction that justice matters.

2.5
Justice, War and Peace: The Ambivalence of the Human Inheritance

The Ambivalence Inside
The impact of the justice issue in society and politics hinges on the ambivalent and contradictory predispositions of the human mind. Here I follow Boehm's summary of this problem. Accordingly, we have inherited the disposition to dominance, submission, and resentment of dominance side by side. Together with our dispositions for prosocial attitudes such as empathy, compassion, a sense of fairness, and the drive for cooperation and community, we harbor in our brain structure dispositions to egotism, nepotism (that is, to show prosocial behavior and accompanying emotions only to a small ingroup) and universally-directed altruism. These dispositions are stratified as they manifest themselves in decreasing strength the wider the circle of possible beneficiaries is. All this is not simply culturally constructed, but "anchored in human nature" (Boehm 2001, pp. 225 ff.; for recent empirical support see Magraw-Mickelson and Gollwitzer 2018). Boehm summarizes: The evolutionary saga ends with a species altruistic enough to cooperate quite efficiently in large or small groups, but at the same time prone to competition and conflict…Our most amazing accomplishments are complex societies that verge on being antlike in their divisions of labor and organic cooperation -and also in their unusual capacity to go to war (Boehm 2001, p. 254).
It goes without saying that, like all genetic dispositions, the ones discussed here are distributed among people unequally: Most individuals have all of them, but in different strengths (McDermott 2014, p. 558). In addition, the preceding discussion indicates that our dispositions are varied and contradictory enough to present the basis for "radically different behavioral outcomes at the level of the phenotype", because they make an almost unlimited variety of combinations possible (Boehm 2001, pp. 236 f.).
One particular dark side of our capability to feel and think in justice terms is our inclination to frame justifications in terms of justice arguments when we explain why we do (or have done) harm to others. They can be framed as dealing out retributive justice to a rule-breaker (including revenge); justifications can also be derived from the inherently unjust nature of our opponent (such as the "unjust enemy" of Immanuel Kant [Müller 2014]). From there it is only a small step to the argument that we were justified in doing harm to a person to prevent or limit harm being done to third parties (protection) or ourselves (self-defense) (Baumeister 1997).
In order to understand the power of the justice factor in politics, it is essential to overcome the methodological individualism that still permeates the social sciences. There is still intense discussion about the possibility of states being "actors", of groups having collective identities or of the masses having shared feelings. For sociologists or economists versed in group experiments or for neuroscientists measuring brain activity during collective experiences the issue has long been settled. In recent years, neuroscientists have identified practices that stimulate regions in the brain whose neuronal circuits trigger particularly intense we-feelings simultaneously among entire groups of participants. These involve synchronous movement or vocal actions such as marching, dancing, singing, rhythmic shouting (e.g., of slogans), etc. (Farmer and Maister 2017, pp. 338 ff.). Taking part in a mass demonstration or in the vocal support of the home team in an exciting football match creates an emotional identity that can be mobilized for good or bad-Hitler knew that all too well (Crawford 2014, p. 536) as did the perpetrators of the Rwanda genocide (Ross 2014). At a more complex level, emotions can be collectivized by institutionalization (Crawford 2014). Collective emotions in this sense-the uniform focusing of emotions by many individuals on the same target-is characteristic of justice claims by groups adhering to identity concepts such as nation, ethnic group, religion, or ideology. These are possibly the most devastating grouping frames in terms of their capability to direct common identity into collective violence against outsiders (Pinker 2011, pp. 824 ff.). Collective emotions can thus also be ascribed to, and mobilized by, states (Mercer 2014).
The collective pursuit of a group's justice claims governs intergroup competition where the potential of aggressive emotions is high (Pinker 2011, pp. 767, 772 f.). The diminishing strength of emotions from individual claims through ingroup claims to outgroup claims contains the potential for a fateful reversal in the case of intergroup justice conflicts: We deny the outgroup the right to make justice claims at all, and frame them as enemies who deny us (our ingroup) what is rightfully ours. The mechanism of collective "evilization" triggers escalatory emotions that end in a "we or they" showdown, where only the complete destruction of the enemy will bring justice (Monroe et al. 2000;Müller 2014). The process is a particularly dangerous variant of the ingroup-outgroup dynamics analyzed by Henry Tajfel and his collaborators, and is a common element of the security dilemma, enemy image production and the escalation of conflicts (Tajfel 1982). Understanding of the biological substrate of the ingroup/outgroup distinction and its evaluative and emotional expression in the human brain has made considerable advances in the last two decades, even though many questions have yet to be answered (Jost et al. 2014;Iyengar and Westwood 2015).
However, the path from "altering" a person/group as part of the process of identity building to evilization, that is to say, drawing the line for violent conflict, has not been determined with finality. As de Waal found in his studies on bonobos (see above), even among primates a clash is not inevitable when two groups meet or when an individual approaches a foreign group. Being "other" does not automatically lead to being designated an enemy, as Tajfel himself observed (Tajfel 1982, p. 16; see also Turner 1978, p. 249;Brewer 1999, p. 434). 10 As Boehm reminded us, empathy and the sense of fairness can extend beyond the core or wider family and include unrelated persons. In a much broader historical context, it is obvious that humans have the capability to imagine bonds and extend borders, possibly not completely arbitrarily, but with a high degree of flexibility. Our innate capability to feel empathy and even altruism towards other people is, in principle, almost unlimited (Batson 2011;Pinker 2011, pp. 859 ff.). For that reason, the triadic structure proposed by Boehm, the differentiation between egotism, nepotism and altruism should not be taken as involving discrete alternatives, but rather as a continuum, in which the range of "altruism" encompasses the inclusion of a few strangers into a small ingroup and extends through middle-sized and large groups to essentially universalistic altruism. If this amazing emotional flexibility of the "expanding circle" which the human brain permits did not exist, the building of ever larger social and political units beyond people's closest kin, for which identity bonds were construed in human history, would not have been possible (Singer 2011). That the bonds (and the emotions which they nurture) become less intense the wider the scope and the more people they encompass might be generally true, but given the enormous intensity of nationalism or common religion as a bonding emotion and the motivational force to use violence in its service shows that scope and intensity are not perfectly correlated, and that even the widening of the circle of empathy, we-feeling, and justice still contains the dark side of excluding those who allegedly don't belong to the group.
It is for this reason that studying techniques and practices that prevent the alienating consequences of ingroup/outgroup dynamics or even roll back prejudices against the "other" are of utmost importance for peacemaking and peacebuilding. Experimental psychological studies have shown that relatively simple pedagogical practices such as perspective-taking (e.g., writing an essay on a conflict from the viewpoint of the other side) change existing brain reactions towards this outgroup for the better. Synchronous movement with people of a prejudiced group produce results similar to what these practices engender in homogeneous groups (see above), thus helping to diminish intergroup social distance. Even more amazing results have been produced by electronic simulation techniques which show that the person being studied was handling an avatar from a prejudiced social group. The resulting process of identification (and concomitant prejudice-deconstruction) appears to be related to the simultaneous challenge of non-conscious (bodily) and conscious (conceptual) parts of the research participant's identity (Farmer and Maister 2017, pp. 337 ff.). Another study found that the asymmetry in empathy between ingroup and outgroup disappeared after a few instances of experiencing (unexpected) help from outgroup members (Hein et al. 2016). Thus, the plasticity of feelings towards the outgroup offers a promising approach for tackling the difficult dilemma of contradictory justice claims distributed across two identity groups. These practices for enhancing empathy towards groups previously regarded as hostile, alien or unpleasant could help to understand the sources of hostile justice claims and to overcome seemingly unalterable antagonistic positions in justice conflicts.

The Ambiguity of Justice
Principally, our disposition for justice is not impartial or symmetrical. Our reading of what is fair is biased in a selfish way, individually as well as collectively (Babcock et al. 1995). Thus we react most strongly when our own individual justice claims are concerned (egotism). We are considerably engaged when those of our ingroup (our close relatives at the top) are involved (nepotism). And we have the capability, still measurable but definitely weaker than the first two, to develop empathy with the justice claims of strangers (including outgroups) (Boehm 2001(Boehm , 2012. It is this latter capability on which the pacifying potential of justice rests. It is the former two capabilities which drive its potential for conflict. The impact of justice issues on human affairs and political relations can therefore apply pressure in two opposite directions. Justice is part of overall morality and one of the highest moral values. As Pinker demonstrates, morality itself is ambiguous (Pinker 2011, pp. 923 ff.). Humans build moral communities along the ingroup-outgroup divide. These moral communities may, but need not, coincide with other bonding characteristics (class, ethnicity, religion, and nation). Since morality is prone to create absolutes, ingroup-outgroup relations quickly produce attitudes of alienation, condescension, and hostility. Boehm adds the bitterly ironic point that morality might be at the root of the extraordinary capacity of the human species to engage in large-scale, immensely costly wars: without morality, individuals could not be shamed into military service, and without altruism, nobody would be willing to sacrifice his/her life for the sake of the community (Boehm 2001, p. 254;Rudolph 2017, pp. 174 f.).
It follows that as a central moral principle, justice in politics is also bound to engender these ambivalent consequences. On the one hand, the settlement of disputes becomes possible, and solutions have a chance of being lasting if and when they satisfy the justice claims of all relevant actors or are perceived by them as reasonably just when the outcomes for all parties are compared (Zartman 1997(Zartman , 2008. On the other hand, incompatible justice claims or contradictory justice principles applied to a specific case may lead to enduring disputes and stimulate high levels of emotion, which make the rational management of conflict difficult or impossible and motivate parties to take recourse to violent behavior (Welch 1993;Müller 2013). In the realm of retributive justice, threatening the perpetrators of atrocities with legal prosecution, for example through the International Criminal Court, may not only sustain motivation to continue violent conflict rather than seek compromise, but can also create secondary justice conflicts through resentment among followers or supporters of perceived arbitrary prosecution of their leaders, but not those of the opposite party (Porok 2017).
Different ideas about what justice means in general or in specific situations are possible because our basic genetic disposition for the "sense of justice" does not determine the substance with which we fill the term "justice" (Druckman 2008). This "filling" takes place during the long socialization process humans are subjected to, and differs among cultures. Different traditions bring about different preferences for principles of justice and different ways of interpreting how they are to be applied: culture matters in presenting the frame in which our dispositions take a particular substantive shape during our socialization (Boehm 2001, pp. 244 f.). 11 As a consequence, there are vastly different ideas in the world-and in the minds and souls of humans-concerning what justice means and how it should be implemented. The well-meaning attempts of philosophers and religious theorists to develop a supposedly universally valid conception of justice from their respective cultural traditions are in vain, because they are trapped in a particular perspective and cannot shake off pluralism of conceptions. Even the most honest attempt to take an "objective position" can never be certain that intrinsic bias has not affected cognition, deliberation and evaluation. 12 When their ideas become part of national cultures, such efforts to create a universal theory with cogent validity may even deepen rifts and stimulate conflict by developing strong dogmas that are hard to overcome, thus influencing political preferences and stimulating a missionary drive towards universalization directed against the justice ideas reigning elsewhere.
There is another area where the human inclination to invest emotions in justice claims against others can trigger an escalatory spiral of violence: an integral part of justice is retributive justice. One important merit of the civilization process is the deprivatization of retributive justice (punishment for wrongdoing) and its takeover by the state. Nevertheless, people's feeling of having been hurt, betrayed, offended, discriminated against, or humiliated by another actor still drives the desire for revenge (Pinker 2011, pp. 783 ff.) even within states governed by the rule of law; it is a very dangerous trigger of violence in fragmented societies where the fragments have strong identities, and it is also strong in the international realm (e.g., Fattah and Fierke 2009). The lust for revenge is the individual emotion which is involved here, and it is coupled with the structures of wrath and aggression in our brain. It can suppress empathy toward the offender, and successful revenge can trigger emotions of happiness, notably in men (Singer et al. 2006). Fortunately, our genetic inheritance contains still another structure which makes us inclined to forgive, and thus dampens the impulse to take revenge when we suffer injustice (McCullough 2008).

Justice, War and Peace
How these ambiguities can combine in an internationally relevant way has been demonstrated by social psychologists (Platow et al. 2014). They polled citizens of Australia, New Zealand, and the United States on how the Olympic performance of national teams should be measured; the standard measure is the total number of Olympic medals. While Americans found it bewildering that anybody could think of anything else than the standard metric, Australians and even more strongly, New Zealanders, believed that this standard was unfair, and that instead population size and/or Gross National Product should be taken into account (e.g., medals per citizen should be the metric applied). Citizens of the three nations were in complete agreement that nations should be compared according to a just standard, but disagreed profoundly on what "just" meant in the given situation, and each nationality chose the measure that would favor the prestige of their own nation. What looks quite harmless in this example can become much more serious in other constellations, of course.
The-largely unconscious-tilting of the sense of justice in our own favor and its use to place outgroups and their members at a disadvantage is part of what Steven Pinker has rightly dubbed "the moralization gap" (Pinker 2011, pp. 721 ff.). Justice as a core value of any moralistic system, and in a consensual or compromise-ready environment favorable for the establishment of lasting peace, can turn into a tool for creating horrific injustice in the very name of justice, all the way to genocidal violence.
It is thus not surprising that in his pioneering study on justice and war David Welch found a strong impact of justice claims and conflicts in most of the major international conflicts between great powers since 1815 (Welch 1993). Nations as imagined communities (Anderson 1991) achieve coherence in their national identities from the feeling that their own ingroup is better than the others. Consequently, their own justice claims (e.g., the claim on territory or for higher status than others) are seen as justified, while equal or equivalent claims by others are not. Since strong emotions are attached to these collective claims, compromising is extremely difficult and leaders who try to commit to compromise risk their reputation, power and-in the extreme case-their life, as Egyptian President Sadat did in the case of the Camp David agreement and Israeli Prime Minister Rabin did in the case of the Oslo Agreement. Currently, we are watching attentively the way in which the Greek and Macedonian leaders are experiencing harsh criticism for their completely reasonable compromise on the decades-old quarrel about the name of Macedonia. The jury is still out on the outcome.
Justice, one of the noblest traits of human beings, hard wired in the brain and imprinted into the mind by socialization and constant practice, can thus degenerate into the stimulus for the worst instincts that our species harbors. On the other hand, empathy for the justice claims of others can help enlightened leaders cut Gordian knots of enduring conflict and find solutions that "do justice" to all claimants, laying to rest deadly quarrels that had prevailed for so long. There is no magic algorithm for granting victory to the "better angels" in our mind, as Steven Pinker put it, and there is no final institutional structure for human affairs that would reliably cause permanent justice and permanent peace. Rather, outcomes depend on practices, and the practitioners are humans with their inexorable bifurcated inclination to do both good and bad in the name of justice, to make peace as well as to make war.

Conclusion
Continuing progress in a variety of sciences will engender a revolution in our own fields of political science, international relations, and peace studies. The mainstream has experienced a taste of the ongoing change, as the 2017 Supplement of International Organization on "The Behavioral Revolution and International Relations" documents. The explicit aim of this collection of articles is to assess the "challenge" posed "to rationalist models" by the "behavioral revolution" that has "swept across the social sciences in the last few decades" (Hafner-Burton et al. 2017, pp. S2 f.). However, as this chapter has shown, the concept of a "behavioral" revolution presented there falls far short of what is really happening. The authors of the introductory article and the authors of most of the remaining papers are seeking ways of integrating insights into empirical human behavior that present "anomalies" in the perspective of the hegemonic behavioral model of rationalism. They accept heterogeneous preferences and risk-taking, take the asymmetrical valuation of losses and gains identified by prospect theory into account, recognize the influence of emotions and beliefs, and amalgamate these innovations with the rationalist model, but in a way that transfers everything new to complementary aspects of "economic man" (Hafner-Burton et al. 2017). The task is then reduced to defining the scope conditions under which rationality prevails and using the complementary explanatory tools to explain extant deviations. Occasionally, it appears to dawn on the authors that more is at stake, such as when they state that findings like motivated reasoning or social preference may "require rethinking the axiomatic foundations of rational choice itself" (Hafner-Burton et al. 2017, p. 18). This insight, however, is not borne out in this volume. Rather, it demonstrates a classic case of Kuhn's "science in crisis", in which scholars work hard to integrate findings into the hegemonic paradigm, while these findings constitute insuperable contradictions to the same paradigm (Kuhn 1962, Chap. 7). 13 In fact, we are not facing just a "behavioral revolution", a term which suggests a change in methods from deductive to inductive research, based on empirical insights into human behavior gained by new methods. We are confronted with an ontological revolution that forces us to reconstruct our image of the human (Crawford 2011). As suggested at the end of the previous section, the human mind is a mixed bag, and its contents are involved in perception, evaluation, and decision making. Morality and emotions always interfere with selfishness and rationality-no supposedly rational cognition or decision occurs without the involvement of emotions (Ellsworth 2014;McDermott 2014, p. 558), even when the prefrontal cortex does most of the work. A new standard model of behavior has to start from this mixed bag and must be freshly constructed from scratch. The rational choice model can serve as the ideal type of a special case, the scope conditions of which have to be carefully researched and determined (Gross Stein 2017), but should not be imposed as the default option of "normalcy" from the outset.
A changed image of the human species that concerns both individual motives and reactions and how they combine to affect the behavior of collectivities from small groups to states (Hutchison and Bleiker 2014;Mercer 2014;Crawford 2011) opens many new roads for our discipline. The central and ambiguous position of the justice issue in politics can be far better explored from this perspective than from the old hegemonic one.
In order to harness the new opportunities scholars will have to do three things: First, to acquire a basic knowledge on the related findings and the paradigms in which they are rooted. Second, to develop practices of interdisciplinary work 13 It is telling that Richard Ned Lebow, who from an early stage had criticized the rationalist paradigm from a perspective emphasizing motivational bias (Lebow 1981) and has constructed an alternative anthropological model in which non-rational drivers (striving for honor, fear) play a central role (Lebow 2008), does not even appear in the huge list of references attached to the introductory article. An alternative standard model is not admitted by those standing guard over the hegemonic paradigm. that go far beyond the sporadic encounters, contacts, and single projects that have been beacons of synthetic insights of great potential but for the most part have not led to systematic joint progress across disciplines. Third, to sincerely sift through the assumptions underlying our established theories and correct them or even abandon them in the light of what is becoming the state of the art elsewhere. Neither economic materialism nor preference-based rationalism, neither "economic man" nor "ideational woman" will stand the test. They can serve, usefully, as ideal types to explore empirical deviations from their idealized assumptions. Their role is reduced to that of being epistemological tools. They cannot be used as ontological templates to decipher the empirical world. The philosophical tradition in which these theories are located have emphasized dichotomies, such as cognition/emotion, deliberation/feeling, selfishness/altruism, empathy/hate. Again, these dichotomies are useful heuristic tools for distinguishing the related sources and expressions of human behavior, that is, epistemological instruments. Ontologically, however, these apparent opposites are mixed and intermingled in the material (biological) basis of human behavior. Our "nature" is thus much more complex and more ambiguous than the traditional simplification into these dichotomies suggests. This makes the analysis of political problems and their solution even more burdened and onerous than the "old" ontologies indicated. It is nevertheless inescapable to include the profound recent insights in human nature into our analysis. The relationship between justice and peace is a good place to start. But the landscape upon which the door is opening is much broader; it encompasses the whole field in which we are working.