The Explosive Mix of Sex and Violence

Risks of violence and sexual assault increase in crowds

Risks of violence and sexual assault increase in crowds

The roving gangs of men who sexually assaulted women during the New Year’s Eve celebration in Cologne, Germany, have ignited outrage across Europe and around the world. (1)  The political implications have been much discussed, but how was this violence triggered in these individuals? These assaults illuminate a dark side of human nature: how sex and violence are interlinked in the human brain.

A perplexing link between human sexual behavior and violence is evident from an early age when boys tease and punch girls (2) they are attracted to.  Some major league baseball players look at pornography right before they go to the plate to increase their level of aggression. Thirty percent of all internet traffic is pornography, and 88 percent of this contains physical aggression. (3) In the extreme, sadistic sexual behavior can develop from the intertwining of sex and violence in the human brain.   As crowds grow and become unruly, especially if alcohol and other drugs are involved, gang sexual assault can erupt with awful spontaneity.

Biologically, sex and violence share a number of common brain states and functions.  Both behaviors evoke intense arousal–indeed, the most intense states of arousal possible.  Fighting and mating share some of the same neural circuits, neurotransmitters and hormones of arousal, and both activities strongly stimulate the brain’s reward and pleasure systems.  This brain circuitry can lead men to seek out violence, to pick fights for no apparent reason other than to derive satisfaction from the rewarding feeling that comes from the shot of dopamine in the brain accompanying aggression.  This is the same neurotransmitter boost produced by cocaine and other drugs of addiction.  The neurotransmitter serotonin is also involved in both sexual gratification and in violence. (4)

The biological underpinning for this intersection between sex and violence is a nasty legacy of our primate ancestors.  Many animals, nonhuman primates among them, use violence to obtain and defend mates.   Both aggression and sex are controlled by neurons in the same part of the brain–the hypothalamic attack region.  When researchers stimulate these neurons with electrodes in the brains of mice, the animals instantly engage in violence or in mating, depending on how strongly the neurons are stimulated.(5)  The abrupt switch between mating and fighting is completely under control of the researchers who can flip the animal from mating to fighting by stimulating these neurons at the right intensity.    It is an unsettling observation.


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