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Cited by 207Primate Behavior and EcologyNeuroendocrine regulation and behaviorEvolutionary Psychology and Human Behavior

Oxytocin reactivity during intergroup conflict in wild chimpanzees

Open access
Samuni, Liran, Preis, Anna, Mundry, Roger, Deschner, Tobias, Crockford, Catherine, Wittig, Roman M.·2017·Proceedings of the National Academy of Sciences
DOI 10.1073/pnas.1616812114PMC PMC5240673
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Abstract

Significance: Warfare is one of the most pervasive problems among human societies, and understanding mechanisms involved in in-group cooperation and favoritism is of paramount importance. Wild chimpanzees share key features of humans’ intergroup conflict, in terms of in-group coordination, coalitionary support, and out-group hostility. The hormone oxytocin may regulate humans’ intergroup conflict, although tests in natural settings are lacking. We found strong evidence that, like in humans, oxytocin is involved in chimpanzee intergroup conflict. Both intergroup conflict anticipation and participation involved high urinary oxytocin levels, irrespective of intragroup affiliations or potential threat by rivals. These results are indicative of similar physiological processes involved in intergroup violence and intragroup support in both species, likely supporting behavior that is adaptive during intergroup conflicts.

AI snapshot

Written from the paper’s full text.

TL;DR

In wild chimpanzees, urinary oxytocin was significantly higher immediately before and during intergroup conflict than in control periods, and intergroup conflict was associated with greater group cohesion. The authors argue that oxytocinergic involvement in in-group/out-group contexts is not uniquely human and may have evolutionary roots shared with chimpanzees.

Key findings

  • Intergroup conflict was associated with higher urinary oxytocin than controls: event model full-null comparison χ² = 51.253, df = 4, P < 0.001; intergroup conflict without affiliation estimate = 1.197, with affiliation estimate = 1.333, both vs control without affiliation.
  • Chimpanzees were less likely to leave the subgroup during intergroup conflict than during matched controls: GLMM χ² = 13.484, df = 1, P < 0.001; estimate ± SE = −1.732 ± 0.446. Fission events were 25 during intergroup conflict vs 65 during controls; individual fissions per period were 0.365 ± 0.694 vs 1.079 ± 0.974.
  • Anticipatory oxytocin was elevated before border patrols: preborder patrol with affiliation vs control with affiliation χ² = 11.132, df = 1, P < 0.001; estimate ± SE = 1.483 ± 0.410. Oxytocin did not differ significantly between preborder patrol and during intergroup conflict with affiliation (χ² = 0.181, df = 1, P = 0.669).
  • Both sexes showed similar oxytocin reactivity across events (event × sex interaction P = 0.580); females participated in 91% of intergroup conflicts in this study. Coordinated hunting also showed higher oxytocin than controls, but intergroup conflict had significantly higher oxytocin than hunting.

Methods

  • Fieldwork at Taï National Park, Ivory Coast, October 2013–April 2014 and September 2014–May 2015, observing well-habituated East and South neighboring chimpanzee groups (Pan troglodytes verus). All-day focal sampling was conducted on 20 adults (5 males and 5 parous females per group), totaling 2,278 observation hours in East group and 2,164 in South group; analysis included n = 482 urine samples, 23.4 ± 14.55 samples per individual.
  • Noninvasive urine collection was used to measure oxytocin by enzyme immunoassay, expressed as pg/mg creatinine, with samples assigned to behaviors occurring within the 15–60 min oxytocin excretion window. Behavioral data included border patrols, intergroup encounters, fissions, grooming, play, hunting, dominance rank via Elo-rating, and GPS-based proximity to territory borders.
  • Statistical analysis used a Poisson GLMM for defection/fission data and linear mixed models for log-transformed urinary oxytocin. The event model included 468 samples from 20 individuals across 296 events; the anticipation model included 52 samples. Models used likelihood ratio tests, random effects for subject and event identity, and random slopes.

Limitations

  • The paper states that the biological validity of peripheral oxytocin measures relative to central oxytocin patterns is debated, though it cites evidence for coordinated central and peripheral release. It also states that the trigger for oxytocin release in intergroup contexts remains unknown, that it is unclear whether oxytocin release results from or precipitates participation in intergroup conflict, and that without a behavioral measure of coordination the authors cannot rule out that oxytocin reactivity merely reflects greater coordination.
  • The paper states that the anticipation model included samples from only one group (East) because no preborder patrol with affiliation samples were obtained for South group, and that group identity was associated with large uncertainty due to the small South group sample size.
  • Evident from the text: the study is observational and correlational, so it cannot establish causality; none of the observed intergroup encounters resulted in lethal aggression, which may limit generalization to lethal intergroup violence.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1073/pnas.1616812114

Cites

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Statistics

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Claims the paper makes

0 of 58 cited sources checked · 0 supported · 0 flagged

  • Findingown data
    § Abstract

    Chimpanzees of both sexes had significantly higher urinary oxytocin levels immediately before and during intergroup conflict compared with controls.

    “We found that chimpanzees of both sexes had significantly higher urinary oxytocin levels immediately before and during intergroup conflict compared with controls.”
    • Also stated in: § Significance · plain
      “Both intergroup conflict anticipation and participation involved high urinary oxytocin levels, irrespective of intragroup affiliations or potential threat by rivals.”
    Quote in the paperSubstantial claim
  • Findingown data
    § Results and Discussion

    During intergroup conflicts, individuals were significantly less likely to leave the subgroup than during control periods.

    “We found that during intergroup conflicts, individuals were significantly less likely to leave the subgroup than during control periods (GLMM, likelihood ratio test: χ2 = 13.484, df = 1, P < 0.001; estimate ± SE −1.732 ± 0.446; Table S1).”
    Quote in the paperSubstantial claim
  • Findingown data
    § Results and Discussion

    South group individuals were significantly less likely to leave the subgroup than East group individuals.

    “We also found an effect of group identity (Table S1), with South group individuals being significantly less likely to leave the subgroup than East group individuals; however, this parameter was associated with some instability.”
    Quote in the paperNot a substantial claim
  • Findingown data
    § Results and Discussion

    Log-transformed urinary oxytocin levels did not differ between border patrols and intergroup encounters.

    “However, log-transformed urinary oxytocin levels did not differ between the two types of intergroup conflict (Table S3; see SI Methods for tests separating these two contexts).”
    Quote in the paperSubstantial claim
  • Findingown data
    § Results and Discussion

    There was no significant effect of affiliation on urinary oxytocin levels within the intergroup conflict context.

    “Moreover, in post hoc analyses comparing intergroup conflict with and without affiliation, we found no significant effect of affiliation on urinary oxytocin levels within this context (LMM: χ2 = 0.136, df = 1, P = 0.334; Table S5).”
    Quote in the paperNot a substantial claim
  • May combine two claims. 23
  • Classified as probably not a substantial claim. 33
  • The quote only partly states this claim. 2

  • May combine two claims.

    Findingown data
    § Results and Discussion

    Neither the presence of affiliation during intergroup conflict nor multipartner affiliation without intergroup conflict led to urinary oxytocin levels that differed from nonaffiliative intergroup conflict or control samples, respectively.

    “Here, neither the presence of affiliation during intergroup conflict nor multipartner affiliation without intergroup conflict (Table 2) led to urinary oxytocin levels that differed from nonaffiliative intergroup conflict or control samples, respectively.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Results and Discussion

    Females participated in 91% of intergroup conflicts in this study (proportion of all adult females and parous females 0.44 ± 0.21 and 0.35 ± 0.2, respectively).

    “females participated in 91% of intergroup conflicts in this study (proportion of all adult females and parous females 0.44 ± 0.21 and 0.35 ± 0.2, respectively).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data
    § Results and Discussion

    Group coordinated hunting behavior had a positive effect on urinary oxytocin levels compared with both control with and without affiliation, although less pronounced than the effect of intergroup conflict.

    “We also found a positive effect of group coordinated hunting behavior on urinary oxytocin levels compared with both the control with and without affiliation, although less pronounced than the effect of intergroup conflict (Table S7).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data
    § Results and Discussion

    The study found an anticipatory increase in urinary oxytocin in wild chimpanzees, similar to the anticipatory testosterone increase previously found in intergroup conflicts and intragroup competition in chimpanzees.

    “Our results demonstrate an anticipatory increase in urinary oxytocin in a similar manner to the anticipatory testosterone increase found in intergroup conflicts (28) and intragroup competition (29) in chimpanzees.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [28] Sobolewski ME, Brown JL, Mitani JC. Territoriality, tolerance and testosterone in wild chimpanzees. Anim Behav. 2012;84(6):1469–1474. [Google Scholar] source

      Not checked in the free run.

    • cites [29] Wobber V, et al. Differential changes in steroid hormones before competition in bonobos and chimpanzees. Proc Natl Acad Sci USA. 2010;107(28):12457–12462. doi: 10.1073/pnas.1007411107. [DOI] [PMC free article] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • May combine two claims.

    Findingown data
    § Results and Discussion

    Both border patrols and intergroup encounters had a significant positive effect on log-transformed urinary oxytocin levels compared with control situations with no positive social interactions.

    “Both types of intergroup conflict had a significant positive effect on log-transformed urinary oxytocin levels (pg/mg creatinine), in contrast to control situations with no positive social interactions [“type” model; linear mixed model (LMM), likelihood ratio test: χ2 = 44.600, df = 2, P < 0.001; Fig. S1 and Table S2].”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Results and Discussion

    The effects of intergroup conflict and coordinated hunting on urinary oxytocin levels were not driven by individual rank or sex, subgroup size, nor proximity to border areas.

    “These effects were neither driven by individual rank or sex, subgroup size, nor proximity to border areas.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Results and Discussion

    Using an ecologically relevant paradigm, the study found that the oxytocinergic system, a highly conserved physiological mechanism, is involved in cohesion during intergroup conflict in chimpanzees, as suggested for humans.

    “Using an ecologically relevant paradigm, we found that the oxytocinergic system, a highly conserved physiological mechanism (5), is involved in cohesion during intergroup conflict in chimpanzees, as suggested for humans (8).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [5] Donaldson ZR, Young LJ. Oxytocin, vasopressin, and the neurogenetics of sociality. Science. 2008;322(5903):900–904. doi: 10.1126/science.1158668. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

    • cites [8] De Dreu CKW, et al. The neuropeptide oxytocin regulates parochial altruism in intergroup conflict among humans. Science. 2010;328(5984):1408–1411. doi: 10.1126/science.1189047. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Abstract

    Wild chimpanzees in almost all long-term field sites engage in competitive intergroup conflicts.

    “Wild chimpanzees in almost all long-term field sites engage in competitive intergroup conflicts (10, 11), which are characterized by two sets of behavior (Movie S1), intergroup encounters and border patrols.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [10] Wilson ML, et al. Lethal aggression in Pan is better explained by adaptive strategies than human impacts. Nature. 2014;513(7518):414–417. doi: 10.1038/nature13727. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

    • cites [11] Boesch C, et al. Intergroup conflicts among chimpanzees in Taï National Park: Lethal violence and the female perspective. Am J Primatol. 2008;70(6):519–532. doi: 10.1002/ajp.20524. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation
    § Abstract

    Intergroup conflict is ubiquitous across human societies and considered crucial for the evolution of humans' large-scale cooperative nature.

    “Intergroup conflict is evident throughout the history of our species, ubiquitous across human societies, and considered crucial for the evolution of humans’ large-scale cooperative nature.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [2] Bowles S. Did warfare among ancestral hunter-gatherers affect the evolution of human social behaviors? Science. 2009;324(5932):1293–1298. doi: 10.1126/science.1168112. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Study design and conductnone given
    § Results and Discussion

    Controls were defined as periods with similar duration, subgroup size, and composition on days that did not include intergroup conflicts or hunting behavior.

    “Controls were defined as periods with similar duration, subgroup size, and composition on days that did not include intergroup conflicts or hunting behavior.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Premisecitation
    § Results and Discussion

    The anxiolytic effect of oxytocin is proposed to facilitate social cohesion during highly risky situations that might otherwise precipitate defection away from threat.

    “The anxiolytic effect of oxytocin is proposed to facilitate social cohesion during highly risky situations that might otherwise precipitate defection away from threat (4).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [4] De Dreu CKW. Oxytocin modulates cooperation within and competition between groups: An integrative review and research agenda. Horm Behav. 2012;61(3):419–428. doi: 10.1016/j.yhbeh.2011.12.009. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Study design and conductown data
    § Results and Discussion

    The event model controlled for individuals' sex and rank, subgroup size, group identity, and proximity to border areas.

    “To control for other factors that might influence hormone levels, we included individuals’ sex and rank, subgroup size, group identity, and proximity to border areas to evaluate potential risk.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Study design and conductcitation
    § Abstract

    Oxytocin concentration of urine samples was measured using an established method to sample specific events.

    “We conducted focal animal sampling (23) for 20 adult male and female chimpanzees of two neighboring groups, and measured the oxytocin concentration of urine samples from all individuals using an established method to sample specific events (19, 20).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [19] Crockford C, et al. Urinary oxytocin and social bonding in related and unrelated wild chimpanzees. Proc Biol Sci. 2013;280(1755):20122765. doi: 10.1098/rspb.2012.2765. [DOI] [PMC free article] [PubMed] [Google Scholar] source

      Not checked in the free run.

    • cites [20] Wittig RM, et al. Food sharing is linked to urinary oxytocin levels and bonding in related and unrelated wild chimpanzees. Proc Biol Sci. 2014;281(1778):20133096. doi: 10.1098/rspb.2013.3096. [DOI] [PMC free article] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Classified as probably not a substantial claim. May combine two claims.

    Study design and conductown data
    § Results and Discussion

    The analysis controlled for group identity, proximity to border areas, and subgroup duration.

    “We controlled for group identity, proximity to border areas where encounters with rivals are more likely, and subgroup duration.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation
    § Abstract

    Chimpanzee group defense is energetically costly in terms of reduced foraging and increased traveling, and risky, as it may lead to injury or death.

    “Chimpanzee group defense is energetically costly in terms of reduced foraging and increased traveling (14), and risky, as it may lead to injury or death (10).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [14] Wilson ML. Chimpanzees, warfare, and the invention of peace. In: Fry DP, editor. War, Peace, and Human Nature: The Convergence of Evolutionary and Cultural Views. Oxford Univ Press; New York: 2013. pp. 361–388. [Google Scholar] source

      Not checked in the free run.

    • cites [10] Wilson ML, et al. Lethal aggression in Pan is better explained by adaptive strategies than human impacts. Nature. 2014;513(7518):414–417. doi: 10.1038/nature13727. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation
    § Abstract

    Intranasal administration of oxytocin enhances in-group cooperation and trust and out-group defensive, but not offensive, competition in men.

    “Intranasal administration of oxytocin enhances in-group cooperation and trust (8, 9) and out-group defensive, but not offensive, competition in men (8).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [8] De Dreu CKW, et al. The neuropeptide oxytocin regulates parochial altruism in intergroup conflict among humans. Science. 2010;328(5984):1408–1411. doi: 10.1126/science.1189047. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

    • cites [9] Israel S, Weisel O, Ebstein RP, Bornstein G. Oxytocin, but not vasopressin, increases both parochial and universal altruism. Psychoneuroendocrinology. 2012;37(8):1341–1344. doi: 10.1016/j.psyneuen.2012.02.001. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation
    § Abstract

    Oxytocin triggers a "tend and defend" form of parochial altruism, accentuating cooperative behavior toward the in-group as well as defensive behavior toward out-groups.

    “This suggests that oxytocin triggers a “tend and defend” form of parochial altruism, accentuating cooperative behavior toward the in-group as well as defensive behavior toward out-groups (4).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [4] De Dreu CKW. Oxytocin modulates cooperation within and competition between groups: An integrative review and research agenda. Horm Behav. 2012;61(3):419–428. doi: 10.1016/j.yhbeh.2011.12.009. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation
    § Abstract

    A contributive mechanism regulating in-group cooperation during intergroup conflicts in humans involves the neuropeptide hormone oxytocin.

    “Studies suggest that a contributive mechanism regulating in-group cooperation during intergroup conflicts in humans involves the neuropeptide hormone oxytocin, known to influence trust, coordination, and social cognition, although evidence from natural settings is lacking.”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [5] Donaldson ZR, Young LJ. Oxytocin, vasopressin, and the neurogenetics of sociality. Science. 2008;322(5903):900–904. doi: 10.1126/science.1158668. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

    • cites [6] Insel TR. The challenge of translation in social neuroscience: A review of oxytocin, vasopressin, and affiliative behavior. Neuron. 2010;65(6):768–779. doi: 10.1016/j.neuron.2010.03.005. [DOI] [PMC free article] [PubMed] [Google Scholar] source

      Not checked in the free run.

    • cites [7] Arueti M, et al. When two become one: The role of oxytocin in interpersonal coordination and cooperation. J Cogn Neurosci. 2013;25(9):1418–1427. doi: 10.1162/jocn_a_00400. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Classified as probably not a substantial claim. May combine two claims.

    Study design and conductown data
    § Abstract

    The study used a within-subjects design, sampling naturally occurring events during intra- and intergroup interactions in wild chimpanzees.

    “We investigated our hypotheses using a within-subjects design, sampling naturally occurring events during intra- and intergroup interactions in wild chimpanzees (Pan troglodytes verus) in the Taï National Park, Ivory Coast.”
    Quote in the paperSubstantial claim

  • May combine two claims. The quote only partly states this claim.

    Interpretationreasoning
    § Significance

    The oxytocinergic system, potentially engendering cohesion and cooperation when facing an out-group threat, may not be uniquely human but rather a mechanism with evolutionary roots shared by our last common ancestor with chimpanzees, likely expediting fitness gains during intergroup conflict.

    “These results are indicative of similar physiological processes involved in intergroup violence and intragroup support in both species, likely supporting behavior that is adaptive during intergroup conflicts.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Study design and conductown data
    § Results and Discussion

    The anticipation model included samples from a single chimpanzee group, East group, because no preborder patrol with affiliation samples were attained for South group.

    “This model included samples from a single chimpanzee group, East group, because no preborder patrol with affiliation samples were attained for South group.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation
    § Abstract

    Successful attacks on rival groups potentially increase the territory size of the in-group and the reproductive output of its members, thereby increasing fitness.

    “Successful attacks on rival groups, however, potentially increase the territory size of the in-group and the reproductive output of its members (14, 15), thereby increasing fitness.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [14] Wilson ML. Chimpanzees, warfare, and the invention of peace. In: Fry DP, editor. War, Peace, and Human Nature: The Convergence of Evolutionary and Cultural Views. Oxford Univ Press; New York: 2013. pp. 361–388. [Google Scholar] source

      Not checked in the free run.

    • cites [15] Mitani JC, Watts DP, Amsler SJ. Lethal intergroup aggression leads to territorial expansion in wild chimpanzees. Curr Biol. 2010;20(12):R507–R508. doi: 10.1016/j.cub.2010.04.021. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Study design and conductown data
    § Results and Discussion

    The anticipation model controlled for duration of grooming, subgroup size, individuals' sex and rank, and proximity to border areas.

    “We fitted an LMM controlling for duration of grooming, subgroup size, individuals’ sex and rank, and proximity to border areas.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Study design and conductcitation
    § Results and Discussion

    All samples relating to a target context were collected within the time window of oxytocin excretion into urine at least 15 min after the start and up to 60 min after the end of interactions.

    “All samples relating to a target context were collected within the time window of oxytocin excretion into urine at least 15 min after the start and up to 60 min after the end of interactions (19, 20).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [19] Crockford C, et al. Urinary oxytocin and social bonding in related and unrelated wild chimpanzees. Proc Biol Sci. 2013;280(1755):20122765. doi: 10.1098/rspb.2012.2765. [DOI] [PMC free article] [PubMed] [Google Scholar] source

      Not checked in the free run.

    • cites [20] Wittig RM, et al. Food sharing is linked to urinary oxytocin levels and bonding in related and unrelated wild chimpanzees. Proc Biol Sci. 2014;281(1778):20133096. doi: 10.1098/rspb.2013.3096. [DOI] [PMC free article] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • The quote only partly states this claim.

    Interpretationown data
    § Abstract

    Elevated urinary oxytocin levels were linked with greater cohesion during intergroup conflicts.

    “Also, elevated hormone levels were linked with greater cohesion during intergroup conflicts, rather than with the level of potential threat posed by rival groups, intragroup affiliative social interactions, or coordinated behavior alone.”
    Quote in the paperSubstantial claim

  • Classified as probably not a substantial claim.

    Premisecitation
    § Results and Discussion

    In a recent study, intranasal administration of oxytocin enhanced in-group cooperation during an in-group out-group setting in both men and women.

    “However, in a recent study, intranasal administration of oxytocin enhanced in-group cooperation during an in-group out-group setting in both men and women (32).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [32] Ten Velden FS, Daughters K, De Dreu CKW. Oxytocin promotes intuitive rather than deliberated cooperation with the in-group. Horm Behav. June 8, 2016 doi: 10.1016/j.yhbeh.2016.06.005. [DOI] [PubMed] [Google Scholar]

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given
    § Results and Discussion

    Proximity to border areas was included by assigning each urine sample a value according to the minimum polygon in which it was excreted.

    “We also included proximity to border areas by assigning each urine sample a value according to the minimum polygon in which it was excreted.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Study design and conductown data
    § Results and Discussion

    VIFs did not reveal collinearity problems, with the largest value being <4 across models.

    “VIFs did not reveal collinearity problems, as indicated by the largest value being <4 (51) (event model 2.59; anticipation model 2.43; defection model 1.98; intergroup conflict type model 2.74; persistence model 2.03; reduced event model 2.72).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [51] Quinn GP, Keough MJ. Experimental Design and Data Analysis for Biologists. Cambridge Univ Press; Cambridge, UK: 2002. [Google Scholar] source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation
    § Results and Discussion

    Oxytocin pathways can involve coordinated central and peripheral oxytocin release, indicating that high peripheral measures reflect the release of central oxytocin.

    “However, an increasing body of evidence shows that oxytocin pathways can involve coordinated central and peripheral oxytocin release, indicating that high peripheral measures reflect the release of central oxytocin.”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [35] McCullough ME, Churchland PS, Mendez AJ. Problems with measuring peripheral oxytocin: Can the data on oxytocin and human behavior be trusted? Neurosci Biobehav Rev. 2013;37(8):1485–1492. doi: 10.1016/j.neubiorev.2013.04.018. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

    • cites [36] Crockford C, Deschner T, Ziegler TE, Wittig RM. Endogenous peripheral oxytocin measures can give insight into the dynamics of social relationships: A review. Front Behav Neurosci. 2014;8:68. doi: 10.3389/fnbeh.2014.00068. [DOI] [PMC free article] [PubMed] [Google Scholar] source

      Not checked in the free run.

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      Not checked in the free run.

  • Classified as probably not a substantial claim. May combine two claims.

    Study design and conductcitation
    § Methods

    Creatinine levels were measured in all urine samples and urinary oxytocin values were expressed as pg/mg creatinine, to control for variation in urine volume and concentration.

    “We measured creatinine levels in all urine samples and expressed urinary oxytocin values as pg/mg creatinine, to control for variation in urine volume and concentration (44).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [44] Bahr NI, Palme R, Möhle U, Hodges JK, Heistermann M. Comparative aspects of the metabolism and excretion of cortisol in three individual nonhuman primates. Gen Comp Endocrinol. 2000;117(3):427–438. doi: 10.1006/gcen.1999.7431. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Study design and conductreasoning
    § Results and Discussion

    Samples were excluded if other social behaviors occurred within the excretion window to ensure greater interpretation accuracy of the results in relation to the specific control and social events.

    “Samples were excluded if other social behaviors occurred within the excretion window to ensure greater interpretation accuracy of the results in relation to the specific control and social events.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductcitation
    § Results and Discussion

    Duration of affiliative contact was included as a control predictor in the anticipation model to control for its effects on urinary oxytocin levels.

    “We also included duration of affiliative contact as a control predictor in the anticipation model (affiliation duration) to control for its effects on urinary oxytocin levels (26).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [26] Lim MM, Young LJ. Neuropeptidergic regulation of affiliative behavior and social bonding in animals. Horm Behav. 2006;50(4):506–517. doi: 10.1016/j.yhbeh.2006.06.028. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductreasoning
    § Methods

    Because very low creatinine values may lead to overestimation of urinary oxytocin levels, all urine samples with creatinine levels ≤0.04 mg/mL were excluded (n = 5, <1.2% of samples included).

    “Because very low creatinine values may lead to overestimation of urinary oxytocin levels, we excluded all urine samples with creatinine levels ≤0.04 mg/mL (n = 5, <1.2% of the samples included).”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductcitation
    § Results and Discussion

    To keep type I error rate at the nominal 5%, random slopes were included for both proximity and period type within-subject.

    “To keep type I error rate at the nominal 5%, we included random slopes (46, 47) for both proximity and period type within-subject.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [46] Barr DJ, Levy R, Scheepers C, Tily HJ. Random effects structure for confirmatory hypothesis testing: Keep it maximal. J Mem Lang. 2013;68(3):255–278. doi: 10.1016/j.jml.2012.11.001. [DOI] [PMC free article] [PubMed] [Google Scholar] source

      Not checked in the free run.

    • cites [47] Schielzeth H, Forstmeier W. Conclusions beyond support: Overconfident estimates in mixed models. Behav Ecol. 2009;20(2):416–420. doi: 10.1093/beheco/arn145. [DOI] [PMC free article] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductown data
    § Results and Discussion

    For cases outside the linear range of the oxytocin standard curve, extraction and analysis were repeated with less volume; overall, 23 cases were excluded for remeasurement outside the linear range or lack of material.

    “For cases that produced results outside of the linear range of the oxytocin standard curve, we repeated the extraction and analysis, applying less volume. Overall, we excluded 23 cases for which remeasurement produced results outside of the linear range or for which no material was left over for remeasurement.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductcitation
    § Results and Discussion

    Oxytocin validations of parallelism and accuracy were conducted and appeared satisfactory.

    “Oxytocin validations of parallelism and accuracy were conducted and appeared satisfactory (19).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [19] Crockford C, et al. Urinary oxytocin and social bonding in related and unrelated wild chimpanzees. Proc Biol Sci. 2013;280(1755):20122765. doi: 10.1098/rspb.2012.2765. [DOI] [PMC free article] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductreasoning
    § Results and Discussion

    Group identity (East or South) was included as a control predictor only in the event model.

    “We included group identity (i.e., East or South) as a control predictor only in the event model.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Study design and conductnone given
    § Results and Discussion

    To control for factors that might influence hormone levels, each model included subgroup size as well as individuals' sex and rank.

    “To control for factors that might influence hormone levels, we included in each model subgroup size as well as individuals’ sex and rank.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Results and Discussion

    Male chimpanzees are more likely to be the victims of lethal intergroup aggression.

    “Male chimpanzees are more likely to be the victims of lethal intergroup aggression (10).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [10] Wilson ML, et al. Lethal aggression in Pan is better explained by adaptive strategies than human impacts. Nature. 2014;513(7518):414–417. doi: 10.1038/nature13727. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Results and Discussion

    These threats may increase the likelihood of female avoidance of intergroup conflicts.

    “may increase the likelihood of female avoidance of intergroup conflicts (13).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [13] Watts DP, Mitani JC. Boundary patrols and intergroup encounters in wild chimpanzees. Behaviour. 2001;138(3):299–327. [Google Scholar] source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation
    § Results and Discussion

    The biological validity of peripheral oxytocin measurements with respect to central oxytocin patterns is debated.

    “The biological validity of peripheral oxytocin measurements with respect to central oxytocin patterns nonetheless is debated (33–35).”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [33] Leng G, Ludwig M. Intranasal oxytocin: Myths and delusions. Biol Psychiatry. 2016;79(3):243–250. doi: 10.1016/j.biopsych.2015.05.003. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

    • cites [34] Macdonald K, Feifel D. Helping oxytocin deliver: Considerations in the development of oxytocin-based therapeutics for brain disorders. Front Neurosci. 2013;7:35. doi: 10.3389/fnins.2013.00035. [DOI] [PMC free article] [PubMed] [Google Scholar] source

      Not checked in the free run.

    • cites [35] McCullough ME, Churchland PS, Mendez AJ. Problems with measuring peripheral oxytocin: Can the data on oxytocin and human behavior be trusted? Neurosci Biobehav Rev. 2013;37(8):1485–1492. doi: 10.1016/j.neubiorev.2013.04.018. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Study design and conductown data
    § Results and Discussion

    Nineteen samples collected in the context of intergroup conflict that overlapped with other behaviors that might influence urinary oxytocin levels were not included in the analysis.

    “Accordingly, n = 19 of the samples collected in the context of intergroup conflict that overlapped with other behaviors that might influence urinary oxytocin levels (n = 15 overlapped with hunting behavior and n = 4 overlapped with food sharing) were thus not included in the analysis.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Study design and conductown data
    § Results and Discussion

    An interaction between event type and sex was initially included in the event model; because it did not reveal a significant effect (P = 0.580), it was excluded and the model was rerun.

    “We initially included an interaction between our test predictor (event type) and sex in the event model; however, because it did not reveal a significant effect (P = 0.580), we excluded this variable and reran the model.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductcitation
    § Results and Discussion

    Random slopes were included for the test predictors (event or anticipation) as well as for subgroup size, rank, and proximity within-subject.

    “We included random slopes (46, 47) for the test predictors (i.e., event or anticipation) as well as for subgroup size, rank, and proximity within-subject.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [46] Barr DJ, Levy R, Scheepers C, Tily HJ. Random effects structure for confirmatory hypothesis testing: Keep it maximal. J Mem Lang. 2013;68(3):255–278. doi: 10.1016/j.jml.2012.11.001. [DOI] [PMC free article] [PubMed] [Google Scholar] source

      Not checked in the free run.

    • cites [47] Schielzeth H, Forstmeier W. Conclusions beyond support: Overconfident estimates in mixed models. Behav Ecol. 2009;20(2):416–420. doi: 10.1093/beheco/arn145. [DOI] [PMC free article] [PubMed] [Google Scholar] source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data
    § Results and Discussion

    Fourteen samples in the context of control with affiliation were not included in the analysis due to overlap with play behavior.

    “Similarly, in the context of control with affiliation, n = 14 samples were not included in the analysis due to overlap with play behavior.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Study design and conductown data
    § Results and Discussion

    Visual inspection of qqplots and residuals plotted against fitted values did not reveal obvious deviations from the assumptions of normally distributed and homogeneous residuals.

    “Visual inspection of qqplots and residuals plotted against fitted values did not reveal obvious deviations from the assumptions of normally distributed and homogeneous residuals.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Study design and conductown data
    § Results and Discussion

    Interassay coefficients of variation of low- and high-value quality controls were 19.1% and 7.6% (n = 44), respectively, whereas intraassay coefficients of variation of low- and high-value quality controls were 12.9% and 8.9%, respectively.

    “Interassay coefficients of variation of low- (50 pg/mL) and high- (250 pg/mL) value quality controls were 19.1 and 7.6% (n = 44), respectively, whereas intraassay coefficients of variation of low- (50 pg/mL) and high- (250 pg/mL) value quality controls were 12.9 and 8.9%, respectively.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation
    § Results and Discussion

    The risk of intergroup infanticide and female hostage taking by rival groups are substantial threats for females.

    “the risk of intergroup infanticide and female hostage taking by rival groups are substantial threats for females (10, 11)”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [10] Wilson ML, et al. Lethal aggression in Pan is better explained by adaptive strategies than human impacts. Nature. 2014;513(7518):414–417. doi: 10.1038/nature13727. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

    • cites [11] Boesch C, et al. Intergroup conflicts among chimpanzees in Taï National Park: Lethal violence and the female perspective. Am J Primatol. 2008;70(6):519–532. doi: 10.1002/ajp.20524. [DOI] [PubMed] [Google Scholar] source

      Not checked in the free run.

48 of 48

  • The authors state this as an assumption.

    An anticipatory oxytocin increase would be adaptive when influencing group cohesion.

    “Owing to the beneficial value of cooperative group action during intergroup conflict, we expect that an anticipatory oxytocin increase would be adaptive when influencing group cohesion.”

  • The paper relies on this without support.

    In the Taï Forest, chimpanzee border patrols are often preceded by grooming with multiple group members.

    “Because in the Taï Forest, chimpanzee border patrols are often preceded by grooming with multiple group members, the majority of preborder patrol samples collected involved grooming interactions.”

  • The paper relies on this without support.

    Evidence from natural settings on oxytocinergic system involvement in intergroup conflict is lacking.

    “although evidence from natural settings is lacking.”
    “Few, if any, studies have involved intergroup contexts and oxytocin in captive or wild nonhuman animals.”
3 of 3

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • Recent research reported increased levels of urinary oxytocin in chimpanzees immediately before and during border patrols and intergroup encounters.

    “Finally, at the hormone level, recent research reported increased levels of urinary oxytocin (OT) — a nine-amino-acid peptide synthesized in hypothalamic cells — in chimpanzees immediately before and during border patrols and intergroup encounters (Samuni et al., 2017).”

    From A neurobiological association of revenge propensity during intergroup conflict (2020) · cites this paper as Samuni et al., 2017

  • The paper showed the first evidence of increased levels of endogenous OT in humans during intergroup conflict that involves physical harm to ingroups caused by an outgroup.

    “Previous research has reported endogenous OT reactivity during intergroup conflict in wild chimpanzees (Samuni et al., 2017), but we showed the first evidence of increased levels of endogenous OT in humans during intergroup conflict that involves physical harm to ingroups caused by an outgroup.”

    From A neurobiological association of revenge propensity during intergroup conflict (2020) · cites this paper as Samuni et al., 2017

  • These findings are consistent with the observations in chimpanzees and provide empirical evidence that intergroup conflict in primates including humans is associated with increased levels of endogenous OT.

    “These findings are consistent with the observations in chimpanzees (Samuni et al., 2017), and provide empirical evidence that intergroup conflict in primates including humans is associated with increased levels of endogenous OT.”

    From A neurobiological association of revenge propensity during intergroup conflict (2020) · cites this paper as Samuni et al., 2017

  • Higher levels of oxytocin in saliva, blood, or urine relate to in-group affiliation and cooperation.

    “higher levels of oxytocin in saliva, blood, or urine relate to in-group affiliation and cooperation (Madden and Clutton-Brock, 2011; Samuni et al., 2017)”

    From Oxytocin promotes coordinated out-group attack during intergroup conflict in humans (2019) · cites this paper as Samuni et al., 2017

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Border-patrol fission mean uses the wrong event count

    Minor

    Table 1 reports 16 fission events across 12 border patrols, which gives 1.333 events per patrol, not 1.454.

    Reported 1.454 · recomputed 1.333333

  • Reported urine samples per individual do not match the total

    Minor

    The stated 482 samples across 20 individuals average 24.1 samples per individual, rather than 23.4. The reported mean instead equals 468 divided by 20, the sample count given for the event model.

    Reported 23.4 · recomputed 24.1

  • Intergroup-encounter fission mean uses the wrong event count

    Minor

    Table 1 reports 9 fission events across 11 intergroup encounters, which gives 0.818 events per encounter, not 0.750. The two subgroup means appear to have been calculated using each other's event counts.

    Reported 0.75 · recomputed 0.818182

  • Post hoc intergroup-encounter contrast has the opposite sign

    Minor

    Table S2 estimates border patrol at 1.321 and intergroup encounter at 1.261 relative to control. Their encounter-minus-patrol difference is −0.060, whereas Table S3 reports +0.060 with border patrol as its stated reference.

    Reported 0.06 · recomputed -0.06

  • Post hoc affiliation test gives two different chi-square values

    Minor

    The text assigns χ2 = 0.136 to the comparison and cites Table S5, but that table gives χ2 = 0.933 for the comparison. The text's 0.136 matches the table's estimate, not its chi-square value.

5 of 5

Cites

Flagged first, then by citations

Research works printed but not linked: 1

  1. J Fox, S Weisberg An R Companion to Applied Regression (SAGE, Thousand Oaks, CA, 2010).

Cited by

Sorted by citations

Related

Authors
Samuni, L., Preis, A., Mundry, R., Deschner, T., Crockford, C., & Wittig, R. M.
Affiliations
Max Planck Institute for Evolutionary Anthropology (DE)
ORCID
Venue
Proceedings of the National Academy of Sciences
Publisher
National Academy of Sciences
Published
2016-12-27
Volume
114
Issue
2
Pages
268-273
ISSN
  • 0027-8424 (ISSN-L)
  • 1091-6490
DOI
10.1073/pnas.1616812114
PMC
PMC5240673
OpenAlex
W2561946978
Semantic Scholar
d93d2ca17bee73a9ce46c7729a6b830ab0a3bea0
Cited by
207
References
52
Citations by year
2026: 9 · 2025: 15 · 2024: 16 · 2023: 51 · 2022: 22 · 2021: 18 · 2020: 27 · 2019: 21 · 2018: 20 · 2017: 8
FWCI
25.41
Type
journal article
Language
en
Open access
Locations
  • Proceedings of the National Academy of Sciences (publishedVersion)
  • Europe PMC (PubMed Central) (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
  • Max Planck Digital Library (submittedVersion)
  • MPG.PuRe (Max Planck Society) (submittedVersion)
Topics
  • Social Sciences › Psychology › Social Psychology › Primate Behavior and Ecology
  • Social Sciences › Psychology › Social Psychology › Neuroendocrine regulation and behavior
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Evolutionary Psychology and Human Behavior
Keywords
oxytocin, intergroup conflict, chimpanzees, group cohesion, in-group cooperation, outgroup threat, primate social behavior, evolution of cooperation, nonhuman primate cognition
MeSH terms
Aggression, Altruism, Animals, Behavior, Animal, Pan troglodytes, Conflict, Psychological, Cooperative Behavior, Female, Group Processes, Interpersonal Relations, Male, Oxytocin, Social Behavior, Trust

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-09.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-09.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

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