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

Michael E. W. Varnum; Amanda P. Kirsch; Daniel J. Beal; Cari M. Pick; Laith Al-Shawaf; Chiara Ambrosio; Maria Teresa Barbato; Oumar Barry; Watcharaporn Boonyasiriwat; Eduard Brandstätter; Suzan Ceylan-Batur; Marco Antonio Correa Varella; Julio Eduardo Cruz; Oana David; Laina Ngom Dieng; Dimitri Dubois; Ana María Fernandez; Silvia Galdi; Oscar Javier Galindo Caballero; Sylvie Graf; Igor Grossmann; David Guzman; Peter Halama; Takeshi Hamamura; Martina Hřebíčková; Ioana Iuga; Lady Javela; Jaewuk Jung; Johannes A Karl; Jinseok P Kim; Michal Kohút; Anthonieta Looman Mafra; Dieynaba Gabrielle Ndiaye; Jiaqing O; Beatriz Perez Sánchez; Eric Roth Unzueta; Muhammad Rizwan; A Timur Sevincer; Eric Skoog; Eunkook M Suh; Daniel Sznycer; Evelina Thunell; Arnaud Tognetti; Ayse K. Uskul; Jaroslava Varella Valentova; Yunsuh Nike Wee; Anja Lundkvist Winter; Torin Peter Young; Danilo Zambrano; Anna Ziska; Douglas T. Kenrick; Mohammad Atari

doi:10.1093/pnasnexus/pgaf239

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

Michael E. W. Varnum^*, Amanda P. Kirsch, Daniel J. Beal, Cari M. Pick, Laith Al-Shawaf, Chiara Ambrosio, Maria Teresa Barbato, Oumar Barry, Watcharaporn Boonyasiriwat, Eduard Brandstätter, Suzan Ceylan-Batur, Marco Antonio Correa Varella, Julio Eduardo Cruz, Oana David, Laina Ngom Dieng, Dimitri Dubois, Ana María Fernandez, Silvia Galdi, Oscar Javier Galindo Caballero, Sylvie GrafIgor Grossmann, David Guzman, Peter Halama, Takeshi Hamamura, Martina Hřebíčková, Ioana Iuga, Lady Javela, Jaewuk Jung, Johannes A Karl, Jinseok P Kim, Michal Kohút, Anthonieta Looman Mafra, Dieynaba Gabrielle Ndiaye, Jiaqing O, Beatriz Perez Sánchez, Eric Roth Unzueta, Muhammad Rizwan, A Timur Sevincer, Eric Skoog, Eunkook M Suh, Daniel Sznycer, Evelina Thunell, Arnaud Tognetti, Ayse K. Uskul, Jaroslava Varella Valentova, Yunsuh Nike Wee, Anja Lundkvist Winter, Torin Peter Young, Danilo Zambrano, Anna Ziska, Douglas T. Kenrick^*, Mohammad Atari (Editor)

^*Corresponding author for this work

Department of Psychology

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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.

Original language	English
Article number	pgaf239
Number of pages	10
Journal	PNAS Nexus
Volume	4
Issue number	8
Early online date	26 Aug 2025
DOIs	https://doi.org/10.1093/pnasnexus/pgaf239
Publication status	Published - Aug 2025

Keywords

siblings
aggression
universal
sex differences

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Varnum, M. E. W., Kirsch, A. P., Beal, D. J., Pick, C. M., Al-Shawaf, L., Ambrosio, C., Barbato, M. T., Barry, O., Boonyasiriwat, W., Brandstätter, E., Ceylan-Batur, S., Correa Varella, M. A., Cruz, J. E., David, O., Ngom Dieng, L., Dubois, D., Fernandez, A. M., Galdi, S., Galindo Caballero, O. J., ... Atari, M. (Ed.) (2025). Commonly observed sex differences in direct aggression are absent or reversed in sibling contexts. PNAS Nexus, 4(8), Article pgaf239. https://doi.org/10.1093/pnasnexus/pgaf239

@article{ccea2c881ba64662906ec2c15de5c0f3,

title = "Commonly observed sex differences in direct aggression are absent or reversed in sibling contexts",

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 = "siblings, aggression, universal, sex differences",

author = "Varnum, \{Michael E. W.\} and Kirsch, \{Amanda P.\} and Beal, \{Daniel J.\} and Pick, \{Cari M.\} and Laith Al-Shawaf and Chiara Ambrosio and Barbato, \{Maria Teresa\} and Oumar Barry and Watcharaporn Boonyasiriwat and Eduard Brandst{\"a}tter and Suzan Ceylan-Batur and \{Correa Varella\}, \{Marco Antonio\} and Cruz, \{Julio Eduardo\} and Oana David and \{Ngom Dieng\}, Laina and Dimitri Dubois and Fernandez, \{Ana Mar{\'i}a\} and Silvia Galdi and \{Galindo Caballero\}, \{Oscar Javier\} and Sylvie Graf and Igor Grossmann and David Guzman and Peter Halama and Takeshi Hamamura and Martina H{\v r}eb{\'i}{\v c}kov{\'a} and Ioana Iuga and Lady Javela and Jaewuk Jung and Karl, \{Johannes A\} and Kim, \{Jinseok P\} and Michal Koh{\'u}t and Mafra, \{Anthonieta Looman\} and Ndiaye, \{Dieynaba Gabrielle\} and Jiaqing O and \{Perez S{\'a}nchez\}, Beatriz and Unzueta, \{Eric Roth\} and Muhammad Rizwan and Sevincer, \{A Timur\} and Eric Skoog and Suh, \{Eunkook M\} and Daniel Sznycer and Evelina Thunell and Arnaud Tognetti and Uskul, \{Ayse K.\} and Valentova, \{Jaroslava Varella\} and Wee, \{Yunsuh Nike\} and \{Lundkvist Winter\}, Anja and Young, \{Torin Peter\} and Danilo Zambrano and Anna Ziska and Kenrick, \{Douglas T.\} and Mohammad Atari",

note = "{\textcopyright} The Author(s) 2025. Published by Oxford University Press on behalf of National Academy of Sciences.",

year = "2025",

month = aug,

doi = "10.1093/pnasnexus/pgaf239",

language = "English",

volume = "4",

journal = "PNAS Nexus",

issn = "2752-6542",

publisher = "Oxford University Press",

number = "8",

}

Varnum, MEW, Kirsch, AP, Beal, DJ, Pick, CM, Al-Shawaf, L, Ambrosio, C, Barbato, MT, Barry, O, Boonyasiriwat, W, Brandstätter, E, Ceylan-Batur, S, Correa Varella, MA, Cruz, JE, David, O, Ngom Dieng, L, Dubois, D, Fernandez, AM, Galdi, S, Galindo Caballero, OJ, Graf, S, Grossmann, I, Guzman, D, Halama, P, Hamamura, T, Hřebíčková, M, Iuga, I, Javela, L, Jung, J, Karl, JA, Kim, JP, Kohút, M, Mafra, AL, Ndiaye, DG, O, J, Perez Sánchez, B, Unzueta, ER, Rizwan, M, Sevincer, AT, Skoog, E, Suh, EM, Sznycer, D, Thunell, E, Tognetti, A, Uskul, AK, Valentova, JV, Wee, YN, Lundkvist Winter, A, Young, TP, Zambrano, D, Ziska, A, Kenrick, DT & Atari, M (ed.) 2025, 'Commonly observed sex differences in direct aggression are absent or reversed in sibling contexts', PNAS Nexus, vol. 4, no. 8, pgaf239. https://doi.org/10.1093/pnasnexus/pgaf239

TY - JOUR

T1 - Commonly observed sex differences in direct aggression are absent or reversed in sibling contexts

AU - Varnum, Michael E. W.

AU - Kirsch, Amanda P.

AU - Beal, Daniel J.

AU - Pick, Cari M.

AU - Al-Shawaf, Laith

AU - Ambrosio, Chiara

AU - Barbato, Maria Teresa

AU - Barry, Oumar

AU - Boonyasiriwat, Watcharaporn

AU - Brandstätter, Eduard

AU - Ceylan-Batur, Suzan

AU - Correa Varella, Marco Antonio

AU - Cruz, Julio Eduardo

AU - David, Oana

AU - Ngom Dieng, Laina

AU - Dubois, Dimitri

AU - Fernandez, Ana María

AU - Galdi, Silvia

AU - Galindo Caballero, Oscar Javier

AU - Graf, Sylvie

AU - Grossmann, Igor

AU - Guzman, David

AU - Halama, Peter

AU - Hamamura, Takeshi

AU - Hřebíčková, Martina

AU - Iuga, Ioana

AU - Javela, Lady

AU - Jung, Jaewuk

AU - Karl, Johannes A

AU - Kim, Jinseok P

AU - Kohút, Michal

AU - Mafra, Anthonieta Looman

AU - Ndiaye, Dieynaba Gabrielle

AU - O, Jiaqing

AU - Perez Sánchez, Beatriz

AU - Unzueta, Eric Roth

AU - Rizwan, Muhammad

AU - Sevincer, A Timur

AU - Skoog, Eric

AU - Suh, Eunkook M

AU - Sznycer, Daniel

AU - Thunell, Evelina

AU - Tognetti, Arnaud

AU - Uskul, Ayse K.

AU - Valentova, Jaroslava Varella

AU - Wee, Yunsuh Nike

AU - Lundkvist Winter, Anja

AU - Young, Torin Peter

AU - Zambrano, Danilo

AU - Ziska, Anna

AU - Kenrick, Douglas T.

A2 - Atari, Mohammad

PY - 2025/8

Y1 - 2025/8

N2 - 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.

AB - 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.

KW - siblings

KW - aggression

KW - universal

KW - sex differences

U2 - 10.1093/pnasnexus/pgaf239

DO - 10.1093/pnasnexus/pgaf239

M3 - Article

C2 - 40874028

SN - 2752-6542

VL - 4

JO - PNAS Nexus

JF - PNAS Nexus

IS - 8

M1 - pgaf239

ER -

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

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Keywords

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