Compared to other mammals, humans exhibit an unparalleled level of cooperation (Fehr & Fischbacher, 2003; Gintis, 2011). Conflicts of interest, however, are an inevitable part of social life. Conflicts can emerge between individuals or groups and are capable of escalating into severe disputes (Ericksen & Horton, 1992; Parker, Royle, & Hartley, 2002; Roscoe, 2009). The success of our large and highly cooperative societies hinges upon our ability to resolve conflicts (Boyd & Richerson, 2009; Glowacki, 2022). As communities expand in size, the frequency of conflicts may escalate due to challenges in communication, including inefficiencies and errors, as well as increased demands for information processing (Johnson, 1982) and increased within-group heterogeneity (Gavrilets, 2015; Hill et al., 2011; Johnson & Earle, 1987). These difficulties can lead to the deterioration and breakdown of cooperative relationships, posing a threat to the viability of the social group. Maintaining human cooperation necessitates the resolution of conflicts and the restoration of cooperative relationships, whether through the efforts of the parties in conflict, third-party intervention, or social institutions (Fitouchi & Singh, 2022; Garfield, Syme, & Hagen, 2020; Singh & Garfield, 2022; Wiessner, 2019). Despite the vital role of conflict resolution in sustaining human cooperation, the mechanisms of conflict mediation and the factors shaping the emergence of conflict mediators remain underexplored. While previous studies conducted among rural, politically acephalous communities have examined the characteristics of conflict mediators, such as their social or physical capital (Glowacki & von Rueden, 2015) and the institutionalization of intra-group conflict resolution through leadership (von Rueden, Gurven, Kaplan, & Stieglitz, 2014), they have not explicitly addressed conflict outcomes. Field research and cross-cultural studies have also explored the nature of conflicts requiring mediation and the influence of socioecological factors on variation in conflict mediation (Garfield & Hagen, 2020; Redhead & Von Rueden, 2021; Wiessner, 2019), but they have not investigated the impact of inter and intra-gender dynamics on third-party mediation. Furthermore, empirical data on conflicts and mediation among politically acephalous, nonindustrial societies are limited.

Conflicts, whether experienced directly between individuals, indirectly through a social partner, or in mediating the conflicts of others, are an inevitable feature of social life (Boehm, 1982; Trivers, 1974). Given the pervasiveness of interpersonal conflicts and our universal ability to resolve them, conflict resolution is also likely a fundamental feature of human societies (Garfield et al., 2020). However, the underlying mechanisms driving variation in the socio-ecology of inter-individual conflicts and their mediation remain unclear. Addressing these questions can provide valuable insights into how human cooperation is maintained amid recurrent inter-individual conflicts.

Interactions between individuals are not random and, as a result, inter-individual conflicts are often non-random as well. Demographic factors, residency patterns, social structures, geography, and economic strategies all contribute to systematic patterns of interaction. Although human family systems exhibit substantial variability (Sear, 2021), the family unit is universal across human societies (Brown, 1991; Walker, Hill, Flinn, & Ellsworth, 2011). Marriage and family practices shape household compositions and can both exacerbate and alleviate inter-individual conflicts. In approximately 85% of documented societies, men are allowed to marry multiple wives (White, 1988). Polygyny, prevalent among East African pastoralists, serves as a means for men to enhance their social status, forge alliances, and accumulate wealth through livestock ownership (Fratkin, 2001; Fratkin, Galvin, & Roth, 1994; Boserup (2007)). Polygyny, however, also intensifies conflicts within groups. Competition among co-wives, reduced relatedness within households, increased spousal jealousy due to diminished paternity certainty, and larger age gaps between spouses are suggested to drive heightened conflict potentials (Henrich, Boyd, & Richerson, 2012). In the context of high rates of polygyny, we can expect increased rates of conflicts between co-wives and their social partners, between unmarried men of similar age and social statuses, and between half-siblings sharing a common biological father but residing in different households.

Economic systems introduce specializations and opportunities for divisions of labor and roles, but they also create new avenues for inter-individual conflict (Bliege-Bird, 1999; Gurven, Winking, Kaplan, von Rueden, & McAllister, 2009). Greater diversification in livelihoods and increased integration of economic and social systems can alter the causes of conflicts experienced by individuals, thereby impacting their nature and potential for resolution. Two significant shifts in economic systems throughout human evolution and among many contemporary rural populations involve increased property ownership (such as domesticated livestock and land ownership) and market integration (involving material wealth and money). In contexts characterized by heightened wealth inequality, conflicts over critical resources tend to be more prevalent, while more economically egalitarian societies may experience a higher incidence of social conflicts (Levine, 1961).

Despite the ever-present threat of interpersonal conflict, humans possess remarkable abilities in resolving conflicts. Biological or affinal kinship can create incentives for cooperation and align the interests of individuals (Hames, 2015). Friendships establish reciprocal patterns of investment, reducing negative socioemotional states (Hruschka, 2010). Cross-cutting sodalities and clan structures formalize membership and social ties, extending familial commitments, expectations, and norms to a broader range of individuals (Glowacki, 2020). Third-party actors also play a crucial role in conflict resolution by facilitating coordination between disputing parties (Boyd & Mathew, 2021; Marlowe et al., 2008; Singh & Garfield, 2022; Wiessner, 2019). While women generally have less social and political influence compared to men across human societies (Low, 1992), older post-menopausal women often emerge as influential local political actors. Leveraging their social and family networks, they assume leadership positions and aid in resolving conflicts within groups (Brown & Kerns, 1985; Garfield, von Rueden and Hagen, 2019). In more gender egalitarian societies, women play an active role in conflict mediation, surpassing their counterparts in more gender-stratified societies. Among the Conambo horticulturalists in Ecuador, women serve as mediators in within-group conflicts, and their involvement enhances the status of men through their wives' participation (Bowser & Patton, 2010). Ethnographic evidence suggests that women mediators may be preferred in more egalitarian communities due to their lower likelihood of escalating conflicts, making them more effective at helping individuals find resolution (Garfield & Hagen, 2020; Lewis, 2014; von Rueden, Alami, Kaplan, & Gurven, 2018). Given women's lower propensity for physical aggression compared to men (Archer, 2004), their involvement can be advantageous in conflict situations where the potential for escalating violence is high.

Understanding how humans resolve interpersonal conflicts is a critical aspect of unraveling the processes that underpin human sociality. Particularly valuable are insights from conflict resolution within politically autonomous and decentralized societies lacking state-based dispute resolution mechanisms. Such societies provide glimpses into the social and cultural processes that have enabled our species' success, considering that much of human evolutionary history unfolded in similar socioecological contexts (Boehm, 1999; Singh & Glowacki, 2022). While no contemporary or ethnographically described politically acephalous, rural community provides a direct analogue to ancestral human societies, empirical data from such communities are invaluable in examining the intricate interplay between culture and psychology in the absence of formal political and state-based institutions. To gain a deeper understanding of the nature of interpersonal conflicts and their resolution, we conducted individual and focus group interviews with members of a subsistence-based community, exploring recent in-group conflicts. Our interviews focused on identifying conflict causes, antagonists, and delving into gender dynamics and the role of third-party mediators.

The Hamar are a semi-autonomous ethnolinguistic group residing in the South Omo Zone of southwest Ethiopia (Petrollino, 2017; Yitbarek, 2020). The majority of Hamar individuals, around 97%, continue to live as rural agro-pastoralists in clusters of rural settlements (Calvert, 2016; Strecker, Lydall, & Baxter, 1984; Wondimu & Woldesemayat, 2020). There is substantial variation among rural Hamar communities today in terms of ecology, demographics, and integration with markets, however, many still uphold and are strongly influenced by traditional social structures and cultural practices (Dubosson, Clack, & Brittain, 2018).

Hamar settlements span both highland and lowland ecologies. The number of households they contain range from a few to over 100, and the spatial arrangement of houses within a settlements varies. Some communities are located closer to market towns, leading to more frequent interactions with tourists as well as governmental and non-governmental organizations. Today, very serious conflicts or legal infractions, such as murder, are likely to involve local police in more market-integrated communities.

Households are organized around a dónza, which means something equivalent to a ‘competent married man.’ These men have attained specific ritual statuses and are recognized as competent, knowledgeable, and productive members of their communities. They actively participate in local political decision-making and generally have a disproportionate influence in the community. They are also economically independent and have the right to develop their own herds and agricultural lands. Individual households, headed by a dónza are associated with other households in close proximity within a cluster of houses called a zarsi. A zarsi functions collectively and its members can coalesce as needed for higher-order community decision-making and coordination. A zarsi may include multiple settlements or hamlets, known as gurda.

Beyond the local settlements, the Hamar are organized into mulda, which are groups of close kin that function collectively in ritual contexts and facilitate marriages. Muldas are further grouped into gertamó, which are patrilineal clans that link individuals across wider geographic ranges, irrespective of their household or settlement (see Strecker, 1976). In rural Hamar communities, most collective decision-making beyond the household occurs at the zarsi level—a group of closely linked households forming a micro-community within a larger network of communities. Each zarsi is embedded within other cross-cutting sodalities, such as age-sets and ritual statuses, which, although culturally significant, have less influence in regulating daily life.

The current study was conducted within a rural Hamar community consisting of one zarsi with two gurdá (settlements or hamlets). At the time of data collection, this community had approximately 177 adult residents and 84 households. It was located approximately 11 km away from the nearest market town, which was about a two-hour walk. This community exhibited limited market integration, with minimal engagement in wage labor and reliance on market-purchased foods, and essentially no exposure to formal education or culturally exogenous religious institutions.