Commonly observed sex differences in direct aggression are absent or reversed in sibling contexts

Michael E W Varnum¹, Amanda P Kirsch¹, Daniel J Beal², Cari M Pick³, Laith Al-Shawaf⁴, Chiara Ambrosio⁵, Maria Teresa Barbato⁶, Oumar Barry⁷, Watcharaporn Boonyasiriwat⁸, Eduard Brandstätter⁹, Suzan Ceylan-Batur¹⁰, Marco Antonio Correa Varella¹¹, Julio Eduardo Cruz¹², Oana David¹³, Laina Ngom Dieng⁷, Dimitri Dubois¹⁴, Ana María Fernandez⁶, Silvia Galdi⁵, Oscar Javier Galindo Caballero¹⁵, Sylvie Graf¹⁶, Igor Grossmann¹⁷, David Guzman¹⁸, Peter Halama¹⁹, Takeshi Hamamura²⁰, Martina Hřebíčková¹⁶, Ioana Iuga¹³, Lady Javela²¹, Jaewuk Jung²², Johannes A Karl^{23

24}, Jinseok P Kim²⁵, Michal Kohút²⁶, Anthonieta Looman Mafra¹¹, Dieynaba Gabrielle Ndiaye⁷, Jiaqing O^{27

28}, Beatriz Perez Sánchez²⁹, Eric Roth Unzueta³⁰, Muhammad Rizwan³¹, A Timur Sevincer³², Eric Skoog³³, Eunkook M Suh²⁵, Daniel Sznycer³⁴, Evelina Thunell³⁵, Arnaud Tognetti^{14

35}, Ayse K Uskul³⁶, Jaroslava Varella Valentova¹¹, Yunsuh Nike Wee³⁴, Anja Lundkvist Winter³⁵, Torin Peter Young¹⁷, Danilo Zambrano¹⁸, Anna Ziska³⁷, Douglas T Kenrick¹

Affiliations

¹ Department of Psychology, Arizona State University, Tempe, AZ 85282-1104, USA.
² Department of Management, Virginia Tech, Blacksburg, VA 24061, USA.
³ Office of the Chief Scientist, Environmental Defense Fund, New York, NY 10100, USA.
⁴ Department of Psychology, Center for Cognitive Archaeology, Lyda Hill Institute for Human Resilience, University of Colorado Colorado Springs, Colorado Springs, CO 80918, USA.
⁵ Department of Psychology, University of Campania "Luigi Vanvitelli", Caserta 81100, Italy.
⁶ School of Psychology, Universidad de Santiago de Chile, Santiago 9170022, Chile.
⁷ Department of Psychologie, University Cheikh Anta Diop, Dakar 10700, Senegal.
⁸ The Faculty of Psychology, Chulalongkorn University, Bangkok 10330, Thailand.
⁹ Institut für Psychologie, Johannes Kepler University Linz, Linz 4040, Austria.
¹⁰ Department of Psychology, TOBB University of Economics and Technology, Ankara 06510, Türkiye.
¹¹ Department of Experimental Psychology, Institute of Psychology, University of São Paulo, São Paulo 05508-030, Brazil.
¹² Department of Psychology, Universidad de los Andes, Bogotá 111711, Colombia.
¹³ The International Institute for the Advanced Studies of Psychotherapy and Applied Mental Health, Babes-Bolyai University Cluj-Napoca, Cluj-Napoca 400347, Romania.
¹⁴ CEE-M, University Montpellier, CNRS, INRAE, Institut Agro, Montpellier 34000, France.
¹⁵ Faculty of Psychology, Universidad Católica de Colombia, Bogotá 110911, Colombia.
¹⁶ Institute of Psychology, Czech Academy of Sciences, Prague 11000, Czechia.
¹⁷ Department of Psychology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
¹⁸ Faculty of Psychology, Fundación Universitaria Konrad Lorenz, Bogotá 110231, Colombia.
¹⁹ Institute of Experimental Psychology, Slovak Academy of Sciences, Bratislava 841 04, Slovakia.
²⁰ School of Psychology, Curtin University, Perth 6102, Australia.
²¹ Department of Psychology, Universidad del Rosario, Bogotá 110311, Colombia.
²² Department of Psychology, Sogang University, Seoul 04107, South Korea.
²³ School of Psychology, Victoria University of Wellington, Wellington 6140, New Zealand.
²⁴ Stanford Graduate School of Business, Stanford, CA 94305, USA.
²⁵ Department of Psychology, Yonsei University, Seoul 03722, South Korea.
²⁶ Department of Psychology, University of Trnava, Trnava 918 43, Slovakia.
²⁷ Department of Psychology, Aberystwyth University, Aberystwyth SY23 3UX, United Kingdom.
²⁸ Department of Psychology, University of Macau, Avenida da Universidade, Taipa 999078, Macao.
²⁹ Department of Psychology, University of La Frontera, Temuco 4780000, Chile.
³⁰ Department of Psychology, Universidad Católica Boliviana, La Paz 0201-0220, Bolivia.
³¹ Department of Clinical Psychology, National University of Medical Sciences, Rawalpindi 46000, Pakistan.
³² Institute of Psychology, Leuphana University of Lüneburg, Lüneburg 21335, Germany.
³³ Peace Research Institute Oslo, Oslo NO-0134, Norway.
³⁴ Department of Psychology, Oklahoma State University, Stillwater, OK 74078, USA.
³⁵ Division of Psychology, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm 171 77, Sweden.
³⁶ School of Psychology, University of Sussex, Brighton and Hove BN1 9RH, United Kingdom.
³⁷ Fresenius University of Applied Sciences, Idstein 65510, Germany.

PMID: 40874028
PMCID: PMC12378733
DOI: 10.1093/pnasnexus/pgaf239

Commonly observed sex differences in direct aggression are absent or reversed in sibling contexts

Michael E W Varnum et al. PNAS Nexus. 2025.

. 2025 Aug 26;4(8):pgaf239.

doi: 10.1093/pnasnexus/pgaf239. eCollection 2025 Aug.

Authors

Affiliations

¹ Department of Psychology, Arizona State University, Tempe, AZ 85282-1104, USA.
² Department of Management, Virginia Tech, Blacksburg, VA 24061, USA.
³ Office of the Chief Scientist, Environmental Defense Fund, New York, NY 10100, USA.
⁴ Department of Psychology, Center for Cognitive Archaeology, Lyda Hill Institute for Human Resilience, University of Colorado Colorado Springs, Colorado Springs, CO 80918, USA.
⁵ Department of Psychology, University of Campania "Luigi Vanvitelli", Caserta 81100, Italy.
⁶ School of Psychology, Universidad de Santiago de Chile, Santiago 9170022, Chile.
⁷ Department of Psychologie, University Cheikh Anta Diop, Dakar 10700, Senegal.
⁸ The Faculty of Psychology, Chulalongkorn University, Bangkok 10330, Thailand.
⁹ Institut für Psychologie, Johannes Kepler University Linz, Linz 4040, Austria.
¹⁰ Department of Psychology, TOBB University of Economics and Technology, Ankara 06510, Türkiye.
¹¹ Department of Experimental Psychology, Institute of Psychology, University of São Paulo, São Paulo 05508-030, Brazil.
¹² Department of Psychology, Universidad de los Andes, Bogotá 111711, Colombia.
¹³ The International Institute for the Advanced Studies of Psychotherapy and Applied Mental Health, Babes-Bolyai University Cluj-Napoca, Cluj-Napoca 400347, Romania.
¹⁴ CEE-M, University Montpellier, CNRS, INRAE, Institut Agro, Montpellier 34000, France.
¹⁵ Faculty of Psychology, Universidad Católica de Colombia, Bogotá 110911, Colombia.
¹⁶ Institute of Psychology, Czech Academy of Sciences, Prague 11000, Czechia.
¹⁷ Department of Psychology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
¹⁸ Faculty of Psychology, Fundación Universitaria Konrad Lorenz, Bogotá 110231, Colombia.
¹⁹ Institute of Experimental Psychology, Slovak Academy of Sciences, Bratislava 841 04, Slovakia.
²⁰ School of Psychology, Curtin University, Perth 6102, Australia.
²¹ Department of Psychology, Universidad del Rosario, Bogotá 110311, Colombia.
²² Department of Psychology, Sogang University, Seoul 04107, South Korea.
²³ School of Psychology, Victoria University of Wellington, Wellington 6140, New Zealand.
²⁴ Stanford Graduate School of Business, Stanford, CA 94305, USA.
²⁵ Department of Psychology, Yonsei University, Seoul 03722, South Korea.
²⁶ Department of Psychology, University of Trnava, Trnava 918 43, Slovakia.
²⁷ Department of Psychology, Aberystwyth University, Aberystwyth SY23 3UX, United Kingdom.
²⁸ Department of Psychology, University of Macau, Avenida da Universidade, Taipa 999078, Macao.
²⁹ Department of Psychology, University of La Frontera, Temuco 4780000, Chile.
³⁰ Department of Psychology, Universidad Católica Boliviana, La Paz 0201-0220, Bolivia.
³¹ Department of Clinical Psychology, National University of Medical Sciences, Rawalpindi 46000, Pakistan.
³² Institute of Psychology, Leuphana University of Lüneburg, Lüneburg 21335, Germany.
³³ Peace Research Institute Oslo, Oslo NO-0134, Norway.
³⁴ Department of Psychology, Oklahoma State University, Stillwater, OK 74078, USA.
³⁵ Division of Psychology, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm 171 77, Sweden.
³⁶ School of Psychology, University of Sussex, Brighton and Hove BN1 9RH, United Kingdom.
³⁷ Fresenius University of Applied Sciences, Idstein 65510, Germany.

PMID: 40874028
PMCID: PMC12378733
DOI: 10.1093/pnasnexus/pgaf239

Erratum in

Correction to: Commonly observed sex differences in direct aggression are absent or reversed in sibling contexts.
[No authors listed] [No authors listed] PNAS Nexus. 2025 Sep 30;4(9):pgaf293. doi: 10.1093/pnasnexus/pgaf293. eCollection 2025 Sep. PNAS Nexus. 2025. PMID: 41036249 Free PMC article.

Abstract

Decades of research support the generalization that human males tend to be more aggressive than females. However, most of that research has examined aggression between unrelated individuals. Data drawn from 24 societies around the globe (n = 4,013) indicate that this generalization does not hold in the context of sibling relationships. In retrospective self-reports, females report being at least as aggressive as males toward their siblings, often more so. This holds for direct as well as indirect aggression, and for aggression between adult siblings as well as aggression that occurred during childhood. Consistent with prior research on sex differences, males reported engaging in more direct aggression toward nonkin than did females in the majority of societies. The results suggest that the dynamics of aggression within the family are different from those outside of it, and ultimately that understanding the role of sex in aggressive tendencies depends on context and target.

Keywords: aggression; sex differences; siblings; universal.

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Figures

**Fig. 1.**
Comparison of female and male direct aggression toward siblings and nonsiblings as both children and adults.

**Fig. 2.**
Comparison of female and male gossiping about siblings and nonsiblings as both children and adults.

**Fig. 3.**
Comparison of female and male reporting siblings and nonsiblings to authority figures as both children and adults.

See this image and copyright information in PMC

References

1. Archer J. 2004. Sex differences in aggression in real-world settings: a meta-analytic review. Rev Gen Psychol. 8(4):291–322.
1. Daly M, Wilson M. Homicide. Routledge, London, 1988.
1. Griskevicius V, et al. 2009. Aggress to impress: hostility as an evolved context-dependent strategy. J Pers Soc Psychol. 96:980–994. - PubMed
1. Irwin V, Wang K, Cui J, Thompson A. Report on indicators of school crime and safety: 2021. NCES 2022-092/NCJ 304625. National Center for Education Statistics, Washington, DC, 2022.
1. Tieger T. 1980. On the biological basis of sex differences in aggression. Child Dev. 51:943–963. - PubMed

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Commonly observed sex differences in direct aggression are absent or reversed in sibling contexts

Affiliations

Commonly observed sex differences in direct aggression are absent or reversed in sibling contexts

Authors

Affiliations

Erratum in

Abstract

Figures

References

LinkOut - more resources

Full Text Sources