Outgroup Individuals Research Articles

Explaining Variation in Challenges to Social Conventions: Black Political Leadership and 'Contraband Camps' in the U.S. Civil War

What explains variation in the extent to which out-group individuals participate in behaviors that challenge existing social orders in ways that fall short of outright contentious politics? In addition to existing explanations that point to technological exposure, institutional change, or leadership attributes, we present a new and complementary explanation. We argue that more significant limitations on a dominant group's ability to police access to informal and formal institutions of power or to regulate participation in privileged activities in a given location cause higher rates of persistent out-group actions that challenge existing social orders. We test our argument using the creation of contraband camps'' during the U.S. Civil War and Reconstruction-era Black political leadership. These camps significantly limited whites' power and control locally, while Black political leadership breached social conventions at the time. Using quantitative analyses that draw on original data collection, we find that relative to counties without such camps, counties with the camps had almost twice as many Black political leaders. Our results shed light on an understudied phenomenon in the U.S. Civil War while also contributing to research on social change.

Variation in aggression rates and urinary cortisol levels indicates intergroup competition in wild bonobos

Intergroup competition is a widespread phenomenon across taxa and groups typically compete over access to limited resources, such as food and mates. Such competition may be quantified by changes in individuals' behavioral and physiological status in response to intergroup encounters (IGEs). Bonobos, one of our closest living relatives, are often regarded as xenophilic and exhibit high tolerance towards out-group individuals. This tolerance between groups may still be accompanied by intergroup competition over resources. We hereby compared variation in aggression rates and urinary cortisol levels of bonobos during and outside contexts of IGEs in the Kokolopori Bonobo Reserve and investigated whether food and mate availability influenced males' and females' aggression and cortisol levels, when controlling for dominance rank and the number of individuals present. We found that although females had higher aggression rates and urinary cortisol levels during than outside contexts of IGEs, these increases were not related to food availability or changes in between-group dynamics when maximally tumescent females were present, rather than absent. Furthermore, males showed higher aggression rates and urinary cortisol levels during than outside contexts of IGEs. However, males' responses during IGEs were not related to the presence of maximally tumescent females and food availability. Taken together, while competition intensified during seemingly tolerant IGEs in bonobos, such competition was unrelated to short-term changes in food and mate availability. Despite physical and physiological costs of aggression, bonobos associate with out-group individuals frequently and for extended periods. This suggests potential benefits of bonobo intergroup associations.

Neighborhood racial demographics predict infants’ neural responses to people of different races

Early in life, greater exposure to diverse people can change the tendency to prefer one's own social group. For instance, infants from racially diverse environments show less preference for their own-race (ingroup) over other-race (outgroup) faces than infants from racially homogeneous environments. Yet how social environment changes ingroup versus outgroup demarcation in infancy remains unclear. A commonly held assumption is that early emerging ingroup preference is based on an affective process: feeling more comfortable with familiar ingroup than unfamiliar outgroup members. However, other processes may also underlie ingroup preference: Infants may attend more to ingroup than outgroup members and/or mirror the actions of ingroup over outgroup individuals. By aggregating 7- to 12-month-old infants' electroencephalography (EEG) activity across three studies, we disambiguate these different processes in the EEG oscillations of preverbal infants according to social environment. White infants from more racially diverse neighborhoods exhibited greater frontal theta oscillation (an index of top-down attention) and more mu rhythm desynchronization (an index of motor system activation and potentially neural mirroring) to racial outgroup individuals than White infants from less racially diverse neighborhoods. Neighborhood racial demographics did not relate to White infants' frontal alpha asymmetry (a measure of approach-withdrawal motivation) toward racial outgroup individuals. Racial minority infants showed no effects of neighborhood racial demographics in their neural responses to racial outgroup individuals. These results indicate that neural mechanisms that may underlie social bias and prejudices are related to neighborhood racial demographics in the first year of life.

Better together? How intergroup associations affect energy balance and feeding behavior in wild bonobos

When the benefits of interacting with out-group members exceed the associated costs, social groups may be expected to be tolerant towards each other. However, in many species exhibiting intergroup tolerance, the nature of benefits gained from intergroup encounters remains unclear. We investigated the potential costs and benefits associated with intergroup associations in bonobos, a species with varying degrees of intergroup tolerance, by testing whether these associations conferred energetic benefits to participants under different socioecological contexts and whether the consequences of these associations substantially differed from within-group competition. We used measures of socioecological factors (fruit abundance and group size), feeding and ranging behaviors, and a physiological marker of energy balance (urinary c-peptide of insulin) collected over a 19-month period from two neighboring wild communities in the Kokolopori Bonobo Reserve, Democratic Republic of the Congo. We found that intergroup associations were not related to individuals’ energy balance, but they were related to variations in individuals’ ranging and feeding behavior. Specifically, bonobos traveled longer distances, visited larger fruit patches, and increased the time spent feeding on fruits on days they associated with the neighboring group. These adaptations in feeding behavior may be strategies to offset the energetic costs of increased travel distances. In the absence of obvious energetic benefits and with clear strategies employed to offset energetic costs, it is likely that intergroup associations in bonobos provide benefits unrelated to energy acquisition, such as social benefits. Our study sheds light on the potential incentives promoting social networks to extend beyond and across groups in a tolerant species.Significance statementIntergroup encounters can be energetically costly due to increased competition over resources. Yet, some species associate with out-group individuals for extended periods of time when the benefits of participating in these associations exceed the potential costs. Bonobos, a species exhibiting intergroup tolerance, modified their feeding behavior during intergroup associations by feeding on larger fruit patches and increasing their time spent feeding on fruits, likely to offset energetic costs of increased travel distances. As results, individuals’ energy balance was not related with intergroup associations. The employment of such strategies in addition to the absence of clear energetic benefits suggests that intergroup associations in bonobos provide social rather than ecological benefits.

Why We Learn Less from Observing Outgroups.

Humans are less likely to learn from individuals belonging to a different group (outgroup) than from individuals of their own group (ingroup), yet the source of this societally relevant deficit has remained unclear. Here we used neuroimaging and computational modeling to investigate how people learn from observing the actions and outcomes of ingroup and outgroup demonstrators. Politically left-wing male and female participants performed worse when observing computer-simulated actions they believed were from a right-wing outgroup member compared with those from a left-wing ingroup member. A control experiment in which participants observed choices from a nonhuman agent confirmed that this performance difference reflected an outgroup deficit, rather than an ingroup gain. Accounting for the outgroup deficit, a computational model showed that participants relied less on information from outgroup actions compared with ingroup actions, while learning from outgroup outcomes was not impaired. At the neural level, the differences in observational ingroup versus outgroup learning were reflected in lateral prefrontal activity. The stronger the activity in this region, the more strongly participants weighed ingroup compared with outgroup learning signals (action prediction errors), which formally captured deficits in outgroup learning. Together, our work provides a computational and neural account of why people learn less from observing outgroups.SIGNIFICANCE STATEMENT Learning from observing others is an efficient way to acquire knowledge. In our globalized world, "the others" often are people from a different social group (outgroup). There is evidence that people learn less from observing outgroup individuals compared with individuals from their own group (ingroup). However, the source of this outgroup deficit in observational learning remained unknown, which limits our chances to improve intergroup learning. Our results showed that participants rely less on observed outgroup actions compared with ingroup actions, while learning from outgroup outcomes is not impaired. On the neural level, this outgroup deficit was reflected in the activation of the inferior frontal gyrus. These findings imply that intergroup learning should rely on observing outcomes, rather than actions.

Enhancing same-gender imitation by highlighting gender norms in Chinese pre-school children.

Children selectively imitate in-group over outgroup individuals under certain experimental conditions. We investigated whether this bias applies to gender in-groups in China. Three- and five-year-olds were shown how to operate novel objects by same-gender and opposite-gender models. Results indicate that the combination of verbally highlighting the gender identity of the model (e.g., 'I am a girl') and making gender norms explicit (e.g., 'girls play this way') significantly enhances high-fidelity imitation. This 'double social effect' was more robust in 5-year-olds than 3-year-olds. Our results underscore how language about gender and the norms for gender-based groups influence behavioural imitation. The pattern of findings enhances our knowledge about pre-schoolers' social learning and imitation as well as the powerful influence of language and group norms on children's voluntary actions and learning.

Fighting for what it’s worth: participation and outcome of inter-group encounters in a pair-living primate, the Javan gibbon (Hylobates moloch)

When resources are limited and defensible, inter-group encounters in animals are often of aggressive nature. Individuals can participate in inter-group encounters to defend mates, infants, and food resources, but also to attract out-group individuals for additional mating opportunities. Since inter-group conflicts have mainly been studied in group-living species, we examined the mate, infant, and food resource defense and mate attraction hypotheses in pair-living Javan gibbons (Hylobates moloch) in Gunung Halimun-Salak National Park, Indonesia. To this end, we investigated factors influencing male and female participation and outcome of encounters (i.e., win vs. lose). We observed 234 complete encounters between three habituated and five unhabituated gibbon groups over 43 months, of which 72% were aggressive. Males were the main participants and they were more likely to participate when cycling females or dependent infants were present, supporting the mate and infant defense hypotheses. Males were also more likely to participate when more fruits were available, contradicting the food resource defense hypothesis. Females participated by singing more often when they were cycling and when there were singing opponents, suggesting an advertisement function of their reproductive status through songs. The probability of winning an inter-group encounter was only higher when cycling females were present, supporting the mate defense hypothesis. The intensity of space use or aggression level had no effect on the outcome of inter-group encounters. Our results highlight that mate and infant defense are crucial for male Javan gibbons, especially in view of their pair-living system, long interbirth intervals, and slow infant development. While animal groups interact aggressively with each other to defend valuable resources, they can also interact to increase additional mating opportunities. Here, we examined male and female participation and the outcomes of inter-group encounters in a wild pair-living primate, the Javan gibbon. Crucially, we found that the presence of cycling females had a significant impact on male participation, female singing, and the outcome of encounters. Our findings suggest that Javan gibbon females may advertise their reproductive status through singing during inter-group encounters while Javan gibbon males rather participate to defend their mates and infants.

Micro-Foundations of the Vanguard: The Origins of Revolutionary Leftist Rebel Groups

What explains the emergence of leftist national liberation rebel groups? I present one causal pathway that unfolded in the early-to-mid-20th century and involved out-group individuals uprooting to imperial metropoles for assimilatory education programs. Once there, out-group individuals experienced discrimination by in-group members of the empire. Discriminatory experiences by imperial in-group members, despite out-group expectations of similar privileges, prompted a series of psychological and behavioral responses that made out-group individuals more likely to accept national liberation—independence and social revolution—as a political goal and adopt leftist ideologies while forming cohesive bonds with other out-group individuals and participating in political agitation. The combination of psychological and behavioral responses resulted in a cohesive, experienced and relatively well-equipped vanguard seeking leftist national liberation. Exploiting as-if random variation in educational experiences of rebel leaders in Eritrea’s Independence War, I quantitatively and qualitatively test mechanisms using archival and primary materials and an original dataset. Results are robust to multiple specifications including out-of-sample qualitative tests that include archival data from four countries. The project illustrates the formation of a highly consequential type of insurgency with implications for the formation of revolutionary jihadist groups.

Effect of Group Size and Individual Characteristics on Intergroup Encounters in Primates

Intergroup encounters are common in nonhuman primates and can vary from affiliative to aggressive. We extracted data from the literature to test five different hypotheses: 1) where there are group size differences between opposing groups, whether the larger group is more likely to win an intergroup encounter than the smaller group; 2) whether the likelihood of a group engaging in aggressive intergroup encounters increases with group size; and 3–5) whether dominant, older individuals, and/or males are more likely to participate aggressively in intergroup encounters than subordinate, younger individuals and/or females. Our data set comprised 52 studies on 31 primate species (3 lemur species, 5 New World monkeys, 19 Old World monkeys, and 4 apes). We found that the larger group is more likely to win an encounter against a smaller group than vice versa. We found no significant relationship between group size and propensity to be aggressive during intergroup encounters. We found weak/no support for the effect of age, dominance rank, and sex on the frequency of aggression displayed toward outgroup individuals during intergroup encounters. Species- and population-specific differences in inter- and intragroup competition and in the degree of the unequal distribution of resources across group members may explain why age, dominance rank, and sex are not strong predictors of aggression during intergroup encounters.

The Interdependent Coexistence of the Rational Civilizations: The Mental Origin of Civilizations

The paper purposes that the three major civilizations are territorial rational civilization originated from the tribes before the Axial Age, discrete Western rational civilization originated from the mega empires in Middle East and Greece during the Axial Age, and the connective Eastern rational civilization originated from the mega empires in India and China during the Axial Age. Territorial rational civilization with territorial worldview for ingroup and outgroup individuals produces territorial nationalist democracy based on rule of boundary to deal with ingroup and outgroup individuals. Discrete Western rational civilization with discrete worldview for discrete and independent individuals produces discrete liberty-equality democracy based on rule of law to deal with discrete individuals. Connective Eastern rational civilization with connective worldview for connective and related individuals produces connective common wellbeing democracy based on rule of relation to deal with connective individuals. The current highly international interdependence produces the purposed internationalized interdependent community which allows the interdependent coexistence of the three rational civilizations by establishing the promotion of rational civilizations, the basic rules of relation and law, the potential civilizational and the regional defense boundaries, and the cooperation in international relations. The mental origin of the rational civilization consists of the social brain for instinctive intragroup relations and worldviews to form the original human social group, the mental immune system for instinctive mental therapy, theory of imaginary mind for imaginary religious and political entities with their own minds to form cohesive large social groups, and the thinking brain for rule to form rational civilization.

Warfare in an evolutionary perspective.

The importance of warfare for human evolution is hotly debated in anthropology. Some authors hypothesize that warfare emerged at least 200,000-100,000 years BP, was frequent, and significantly shaped human social evolution. Other authors claim that warfare is a recent phenomenon, linked to the emergence of agriculture, and mostly explained by cultural rather than evolutionary forces. Here I highlight and critically evaluate six controversial points on the evolutionary bases of warfare. I argue that cultural and evolutionary explanations on the emergence of warfare are not alternative but analyze biological diversity at two distinct levels. An evolved propensity to act aggressively toward outgroup individuals may emerge irrespective of whether warfare appeared early/late during human evolution. Finally, I argue that lethal violence and aggression toward outgroup individuals are two linked but distinct phenomena, and that war and peace are complementary and should not always be treated as two mutually exclusive behavioral responses.

Your Performance Is My Concern: A Perspective-Taking Competition Task Affects ERPs to Opponent's Outcomes.

Previous research has shown that people have more empathic responses to in-group members and more schadenfreude to out-group members. As a dimension of cognitive empathy, perspective-taking has been considered to be related to the enhancement of empathy. We tried to combine these effects through manipulation of a competitive task with opponents and an in-group partner and investigated the potential effect of in-group bias or the perspective-taking effect on outcome evaluation. We hypothesized that the neural activities would provide evidence of in-group bias. We tested it with a simple gambling observation task and recorded subjects’ electroencephalographic (EEG) signals. Our results showed that the opponent’s loss evoked larger feedback-related negativity (FRN) and smaller P300 activity than the partner’s loss condition, and there was a win vs. loss differential effect in P300 for the opponent only. The principal component analysis (PCA) replicated the loss vs. win P300 effect to opponent’s performance. Moreover, the correlation between the inclusion of the other in the self (IOS) scores and FRN suggests perspective-taking may induce greater monitoring to opponent’s performance, which increases the win vs. loss differentiation brain response to the out-group agent. Our results thus provide evidence for the enhanced attention toward out-group individuals after competition manipulation, as well as the motivation significance account of FRN.

Inter-group aggressive interaction patterns indicate male mate defense and female cooperation across bonobo groups at Wamba, Democratic Republic of the Congo.

Although conflicts between groups over valuable resources are common in the animal kingdom, an individual's strategy toward out-group individuals may differ according to the benefits and costs received from inter-group interactions. Groups of bonobos encounter each other frequently and may mingle and range together from a few hours to a few days. During these inter-group associations, individuals across groups exhibit both aggressive and affiliative interactions. This study aimed to examine the strategies that bonobos employ with other groups, by comparing the patterns of within- and inter-group aggression. We observed the aggressive interactions within a group of wild bonobos and between the group and three neighboring groups in Wamba, Luo Scientific Reserve, DR Congo. Bonobos increased the level of cooperation to attack out-group individuals more than they do to attack within-group individuals. Additionally, they reduced the aggression between within-group members during inter-group associations, compared to that when not associated with other groups. Males selectively and cooperatively attacked out-group males. Inter-group aggression among females was rare. Furthermore, females sometimes formed coalitions with out-group individuals to attack a common target. Our results support the hypothesis that inter-group competition occurs in bonobos, with males across groups competing over mates. Females across groups were tolerant and even cooperative with each other. Regardless of the ideal male strategy, female tolerant and cooperative relationships across groups and female within-group superiority over males could preserve tolerant inter-group relationships in bonobos.

Exploring the genetic diversity of jackfruit (Artocarpus heterophyllus Lam.) grown in Uganda based on SSR markers

Artocarpus heterophyllus Lam. is an economically important tree crop that is widely cultivated in Uganda for its fruit. Despite its economic importance, little is known about the genetic diversity of jackfruit in the country. This puts the crop’s genetic resource at risk as farmers selectively grow varieties based on market demand. The study analyzed the genetic diversity of A. heterophyllus trees from 12 districts belonging to three agro-ecological zones and three political regions of Uganda. Ten SSR loci were used to assess the genetic relationship among 200 trees, 197 from Uganda and 3 out-group individuals. All SSR loci were polymorphic with an average of 10.9 alleles per locus. STRUCTURE analysis proposed two genetic clusters: Cluster 1 was composed of samples from Eastern and neighboring Central districts, and Cluster 2 which constituted out-groups and samples from Western and neighboring Central districts. Results of STRUCTURE analysis were confirmed by PCoA. Mbarara District exhibited the highest genetic diversity (He = 0.79, I = 1.71), while Kamuli (He = 0.61, I = 1.08 and Pallisa (He = 0.59, I = 1.12) displayed the lowest genetic diversity despite high abundances of jackfruit trees. Molecular variation was higher within populations than among populations. Moderate and significant genetic differentiation was registered among geographical zones, while varietal differences displayed little insignificant genetic differentiation. Soft and white pulped varieties, considered inferior on the market, harbored private alleles which may be genetically valuable resources. Therefore, sustainable utilization and conservation efforts of the jackfruit genetic resource should consider preserving inferior varieties for future crop improvement.

In-group and out-group perspectives A cross-cultural comparison of four countries

As the interrelationships among countries are increasing in various social, political, educational, and commercial contexts, it would be beneficial to understand how people of different cultures perceive the links of human relationships and how they present different behaviors toward in-group and out-group individuals. By conducting questionnaire, the present study aims to explore the differences in in-group and out-group perceptions and behavioral patterns of private organization employees in South Korea, Japan, Canada, and the United States. Statistical analysis of the collected data yielded cultural differences of human relationships based on in-group and out-group distinctions. To obtain more generally applicable findings, however, further investigation should examine other factors such as age, geographical locations, education, and occupations.

The role of intergroup biases in children’s endorsement of information about novel individuals

A great body of evidence suggests that children are remarkably selective in accepting information from different sources. Yet, very few studies have focused on children’s learning about the attributes of others. In three experiments, we examined how 6- and 7-year-olds’ ingroup and outgroup biases about novel target individuals and their biases to follow ingroup informants interact in social learning contexts. Overall, children exhibited a positivity bias, accepting positive testimony about ingroup and outgroup targets, but this bias was significantly higher for ingroup targets. Furthermore, whereas children accepted the positive testimony about ingroup targets regardless of the informant’s group membership, children selectively relied on ingroup informants when endorsing information about outgroup targets. These results suggest that children’s existing biases interact with their acquisition of knowledge in complex ways and shape their social evaluations. These findings may have important implications for developing strategies to prevent negative biases against outgroup individuals among children.

Species delimitation in the presence of strong incomplete lineage sorting and hybridization: Lessons from Ophioderma (Ophiuroidea: Echinodermata)

Accurate species delimitation is essential to properly assess biodiversity, but also for management and conservation purposes. Yet, it is not always trivial to accurately define species boundaries in closely related species due to incomplete lineage sorting. Additional difficulties may be caused by hybridization, now evidenced as a frequent phenomenon. The brittle star cryptic species complex Ophioderma longicauda encompasses six mitochondrial lineages, including broadcast spawners and internal brooders, yet the actual species boundaries are unknown. Here, we combined three methods to delimit species in the Ophioderma longicauda complex and to infer its divergence history: (i) unsupervised species discovery based on multilocus genotypes; (ii) divergence time estimation using the multi-species coalescent; (iii) divergence scenario testing (including gene flow) using Approximate Bayesian Computation (ABC) methods. 30 sequence markers (transcriptome-based, mitochondrial or non-coding) for 89 O. longicauda and outgroup individuals were used. First, multivariate analyses revealed six genetic clusters, which globally corresponded to the mitochondrial lineages, yet with many exceptions, suggesting ancient hybridization events and challenging traditional mitochondrial barcoding approaches. Second, multi-species coalescent-based analyses confirmed the occurrence of six species and provided divergence time estimates, but the sole use of this method failed to accurately delimit species, highlighting the power of multilocus genotype clustering to delimit recently diverged species. Finally, Approximate Bayesian Computation showed that the most likely scenario involves hybridization between brooders and broadcasters. Our study shows that despite strong incomplete lineage sorting and past hybridization, accurate species delimitation in Ophioderma was possible using a combination of complementary methods. We propose that these methods, especially multilocus genotype clustering, may be useful to resolve other complex speciation histories.

Relatedness and spatial distance modulate intergroup interactions: experimental evidence from a social rodent.

Kin selection theory predicts that individuals should generally behave less aggressively or more amicably towards relatives than nonkin. However, how individuals treat conspecifics depends on genetic relatedness but also on the ecological context, which influences the benefits and costs of their interactions. In this study, we used microsatellite DNA markers and behavioral tests to examine the influence of kinship and proximity on the social behavior of Mongolian gerbils Meriones unguiculatus living in different social groups, and whether these effects varied with sex and season. We recorded the duration of 4 behavioral categories (investigative, neutral, amicable, and agonistic) during a 10-min pairwise test. We found that genetic relatedness had significant effects on the duration of investigative, neutral, and amicable behavior, but not on agonistic behavior. We also found significant interaction effects of relatedness and distance between burrow systems (i.e., spatial distance) on investigative, neutral, and amicable behavior, which suggests that the effects of kinship on social behavior were restricted by spatial proximity. The interaction effect between sex and relatedness on amicable behavior showed that male gerbils became more intimate with individuals of the same sex that had higher pairwise relatedness than females. Furthermore, both male and female gerbils enhanced their aggression during the food-hoarding season, but the intensity of these changes was significantly higher in females. Overall, our results suggest that the effects of kinship and spatial proximity on social behavior exhibit sexual or seasonal patterns, thereby implying ecological context-dependent responses to out-group individuals in Mongolian gerbils.

They're all the same, sometimes: Prejudicial attitudes toward Muslims influence motivated judgments of entitativity and collective responsibility for an individual's actions

Are groups responsible for the actions of individual members? Previous research suggests that people use judgments about the entitativity of an outgroup when judging its collective responsibility for the actions of its members. But do these judgments of outgroup entitativity change when outgroup individuals engage in positive vs. negative deeds? We argue that people make motivated judgments of outgroup entitativity based on their pre-existing attitudes toward the outgroup and the valence of outgroup members' actions. In both a first study and a pre-registered replication, we find that when people have positive attitudes toward Muslims, they judge Muslims to be lower in entitativity following a Muslim's negative action and higher in entitativity following a Muslim individuals' positive action, thus holding Muslims responsible for positive, but not negative individual actions. We also find a weaker mirror pattern of effects for those who have negative attitudes toward Muslims.

Group and kin recognition via olfactory cues in chimpanzees (Pan troglodytes).

Primates were traditionally thought to have a reduced sense of smell. Although there is now evidence that olfaction plays a greater role in primate social life than previously assumed, research on the sense of smell in non-human apes is scarce. Chimpanzees sniff the ground and vegetation on boundary patrols, but the function of this behaviour is unclear. Since chimpanzees are highly territorial and can kill individuals that do not belong to their own community, sniffing might function to gather information about conspecifics, particularly concerning group membership and kinship. To investigate whether chimpanzees recognize group members and kin via olfactory cues, we conducted behavioural bioassays on two groups of chimpanzees at Leipzig Zoo. In a pilot study, we found that chimpanzees responded more strongly to urine than to faeces or body odour. We then presented urine from group members, outgroup individuals and an unscented control in aerated boxes using a simultaneous discrimination task. The first behaviour after a chimpanzee first approached a box was related to olfaction (sniffing, nose within 20 cm, licking) in 83% of cases, highlighting the importance of olfaction as a general investigation mechanism in this species. Chimpanzees sniffed significantly longer at urine stimuli than the control and significantly longer at odours from outgroup individuals than those from group members. Furthermore, the duration of sniffing was positively correlated with relatedness. Our results suggest that chimpanzees use olfactory cues to obtain information about social relationships and fill a gap in our understanding of primate chemical communication.