Sisters with Sharp Elbows: Global Study Reveals Women Are Often More Aggressive Than Brothers
Wednesday, September 17, 2025. This is for Parker, one of my clients at the clinic, his sister Emily, and Sharon, their mom, who tries to keep the peace.
New sibling rivalry research overturns the old belief that men are naturally more aggressive, showing women often outpace brothers in family conflicts.
Aggression has always been handed out along gendered lines.
Men were assigned the part of the violent instigator—fighters, warriors, brawlers.
Women were cast as nurturers, peacekeepers, and emotional glue.
Psychology, too, happily co-signed this story, reporting again and again that men were more aggressive than women, bolstered by reams of statistics from bar fights, playgrounds, and prisons (Archer, 2004; Bettencourt & Miller, 1996).
But stories are not science.
A new global study published in PNAS Nexus brings the myth to its knees. Surveying more than 4,000 people in 24 countries, the researchers found that women were just as aggressive as men toward their siblings—and often more so (Kenrick et al., 2025).
Aggression, it seems, is not simply male turf. Inside families, sisters often sharpen their elbows more than brothers.
Public vs. Private Aggression
Gender differences in aggression look clear in public, but inside families, sisters often lead in yelling, tattling, and conflict.
In public life, the stereotype still holds. Men dominate the crime reports and fill the data charts on physical aggression. Testosterone, evolutionary competition for status, and cultural scripts that reward male bravado all keep the pattern intact (Archer, 2004). Women are discouraged, punished, or pathologized for overt aggression, which helps explain why they appear less often in the public record.
But sibling rivalry research tells a different story.
Within families, women yell more, gossip more, and report their siblings’ misbehavior more often than men. This finding held across vastly different societies—from Sweden to Chile to Pakistan (Kenrick et al., 2025). The psychology of strangers, so carefully mapped out in textbooks, collapses once the target is kin.
Evolutionary Logic: The Pop-Tart Wars
Evolutionary psychology explains sibling aggression as competition for scarce parental resources, not just a male trait.
Evolutionary psychology provides one lens. Siblings are not rivals for mates or status, but for scarce parental resources—attention, affection, food, or the larger bedroom. Richard Trivers (1974) called this parent-offspring conflict: the idea that even cooperation among kin is shadowed by competition.
Frank Sulloway (1996) added that birth order and family size magnify these rivalries, shaping personality and behavior in ways that echo through adulthood. What looks like petty squabbling is, in evolutionary terms, a strategic contest over survival and identity.
In this theater, sisters emerge as equal or stronger competitors. Boys may be punished more severely for aggression, while girls refine other tools—tattling, baiting, yelling, gossiping, and subtler maneuvers (Maccoby, 1998). It is not that women are less aggressive. It is that their aggression has historically taken decidedly different forms.
Parenting Styles and Sibling Conflict
Studies show parenting style predicts sibling rivalry, with authoritarian and neglectful homes fueling aggression between sisters and brothers.
Recent research confirms that aggression in sibling relationships is not just evolutionary—it is also learned. A large meta-analysis of over 14,000 participants found that parenting style significantly predicts the level of sibling conflict (Liu et al., 2022). Authoritative parents, who balance warmth and discipline, raise children with less sibling aggression. Neglectful or authoritarian parents, by contrast, fuel conflict.
This is where gender differences become even sharper. Parents tend to punish boys more for overt aggression, while interpreting girls’ aggression as “emotional” or “bickering” (Maccoby, 1998). The global findings of greater female aggression toward siblings may partly reflect these profoundly subtle asymmetries in parenting.
Stress and the Family Battleground
Research during COVID-19 proves sibling aggression spikes under stress, highlighting how situational pressures shape family conflict.
Sibling aggression is not static. It rises and falls with context. Context, as I have often said ad nauseum, is everything.
During the COVID-19 lockdowns, for example, rates of sibling violence spiked.
A study of family dynamics during the pandemic found that physical and emotional sibling aggression increased dramatically when children were confined to homes under stress (Perkins et al., 2021).
This makes sense: the more pressure a family faces, the more likely children are to take it out on one another. Aggression is not a trait etched into chromosomes. It is situational, responsive to parenting, stress, and social conditions.
Sibling Aggression as a Public Health issue
Recent scholarship reframes sibling violence as a widespread public health problem, not harmless childhood squabbling.
For too long, sibling aggression has been dismissed in American culture as “normal rivalry” or even treated as a developmental rite of passage. But recent scholarship challenges that dismissal. The American Journal of Public Health has described sibling aggression and abuse as an “invisible and widespread public health problem” (Tucker et al., 2024). I can tell you that in my role in public health, I am often confronted with toxic sibling rivalry involving sisters.
The costs are not trivial.
Sibling aggression predicts later mental health struggles, strained family relationships, and even increased vulnerability to bullying and intimate partner violence. When sisters and brothers fight, they are not merely rehearsing for adulthood; they are shaping it.
Adult Siblings: The Rivalry Doesn’t Vanish
Gender still shapes sibling tensions well into adulthood, with daughters reporting higher conflict than sons after major family losses.
If you imagine these dynamics taper off after adolescence, think again. A 2023 study of families coping with parental death found that daughters—but not sons—reported increases in sibling tension after their mothers died (Suitor et al., 2023). Even in adulthood, and under conditions of grief, gender shapes the contours of sibling conflict. Aggression in sibling relationships is not a childish phase but a persistent thread woven into family life.
Literature, Media, and the “Sisterly Love” Bullshit Myth
From Shakespeare to reality TV, culture has always shown sisters as rivals, long before science caught up with the data.
Deep down, humans have always known this.
Shakespeare’s King Lear gave us Regan and Goneril, sisters whose sibling rivalry drove a kingdom into ruin. Louisa May Alcott’s Little Women dramatized the burning of Jo’s manuscript by her jealous sister Amy—an act so devastating that readers still shudder.
Modern media is no different.
From Downton Abbey’s poisonous sibling rivalries to reality television’s endless supply of feuding sisters, the cultural record is clear: “sisterly love” has sometimes been accompanied by sharp elbows and sharper tongues. What this new research does is validate our collective cultural intuition with hard data.
Methods: Imperfect but Pretty Persuasive
Even with self-report surveys, global sibling rivalry studies show consistent patterns of female aggression across cultures.
Yes, the global study relied on self-reports.
Memory bias, cultural differences in interpreting aggression, and social desirability could distort the results.
But the researchers anticipated this.
They asked participants not only to report their own aggression but also to recall their siblings’ behavior. The patterns converged. Brothers and sisters alike agreed that sisters were just as aggressive, if not more so (Kenrick et al., 2025).
This agreement strengthens the case. When both parties tell the same story, it is harder to dismiss as bias.
Why This Matters
Sibling rivalry research challenges gender stereotypes, reframes family conflict, and calls for a new understanding of aggression.
The findings destabilize two assumptions: that men are universally more aggressive, and that families are havens of altruism where kinship mutes hostility. Neither holds. Aggression is situational, relational, and highly dependent on context (Campbell, 2013).
For psychology, this means decades of research may have overlooked the significance of kinship. For public health, it means sibling aggression must be taken seriously, not brushed off as childhood drama. For culture, it means discarding the sentimental caricature of “sisterly love” and replacing it with a portrait that is both more honest and more human.
The research is clear: sisters are not angels in gingham dresses. They are competitors, strategists, and sometimes ruthless opponents. Their aggression may not end in police reports, but it leaves its mark—in the form of slammed doors, whispered gossip, and the occasional scar.
So let us retire the illusion of the perpetually gentle sister.
Real sisters do love—but they also fight, plot, and occasionally burn the metaphorical manuscript. Maybe we can call it affection, but with sharp elbows.
Be Well, Stay kind, and Godspeed.
REFERENCES:
Archer, J. (2004). Sex differences in aggression in real-world settings: A meta-analytic review. Review of General Psychology, 8(4), 291–322. https://doi.org/10.1037/1089-2680.8.4.291
Bettencourt, B. A., & Miller, N. (1996). Gender differences in aggression as a function of provocation: A meta-analysis. Psychological Bulletin, 119(3), 422–447. https://doi.org/10.1037/0033-2909.119.3.422
Campbell, A. (2013). A mind of her own: The evolutionary psychology of women. Oxford University Press.
Kenrick, D. T., Varnum, M. E. W., Kirsch, A. P., Beal, D. J., Pick, C. M., Al-Shawaf, L., Ambrosio, C., ... & Ziska, A. (2025). Commonly observed sex differences in direct aggression are absent or reversed in sibling contexts. PNAS Nexus, 4(9). https://doi.org/10.1093/pnasnexus/igad999
Liu, C., Tan, W., Zhang, J., Wu, Y., & Jiang, F. (2022). Relationships between parenting style and sibling conflicts: A meta-analysis. Frontiers in Psychology, 13, 936253. https://doi.org/10.3389/fpsyg.2022.936253
Maccoby, E. E. (1998). The two sexes: Growing up apart, coming together. Harvard University Press.
Perkins, N. H., Halpern, H., & Swenson, C. (2021). Physical and emotional sibling violence in the time of COVID-19. Journal of Family Violence, 36(7), 863–875. https://doi.org/10.1007/s10896-021-00278-3
Suitor, J. J., Gilligan, M., Rurka, M., & Pillemer, K. (2023). How gender shapes sibling tension in adulthood after parental deaths. Journal of Family Issues, 44(7), 1743–1766. https://doi.org/10.1177/0192513X231176273
Sulloway, F. J. (1996). Born to rebel: Birth order, family dynamics, and creative lives. Vintage.
Trivers, R. L. (1974). Parent-offspring conflict. American Zoologist, 14(1), 249–264. https://doi.org/10.1093/icb/14.1.249
Tucker, C. J., Finkelhor, D., Turner, H. A., & Shattuck, A. (2024). Sibling aggression and abuse: An invisible and widespread public health problem. American Journal of Public Health, 114(3), 240–248. https://doi.org/10.2105/AJPH.2024.307983