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The evolutionary roots of intimate partner violence?
Among the Tsimané people of Bolivia, women who experience intimate partner violence give birth to more children on average than those who do not, suggests a paper published online this week in Nature Human Behaviour.
Intimate partner violence is a widespread phenomenon, despite it causing direct harm to an individual’s reproductive partner. Many behavioural and socio-economic factors have been associated with such violence — including education levels, the status of women’s rights and alcohol/drug abuse. Although these factors are important triggers of intimate partner violence, it remained uncertain whether there could be underlying, evolutionary mechanisms.
Jonathan Stieglitz and colleagues interviewed 105 heterosexual women from five villages of the indigenous Tsimané people, in the Bolivian Amazon — a culture with no strong history of violence or male social dominance. They find that women who experience intimate partner violence in their marriage give birth to more children on average than those who do not. This pattern holds irrespective of the couple’s exposure to intimate partner violence as children and the male partners’ history of violence against other men. With previous work showing that Tsimané women report preferring smaller family sizes on average than men, the authors suggest that intimate partner violence may increase relationship fertility when there is disagreement over ideal family sizes.
The study focused on both the ultimate, or evolutionary, drivers of intimate partner violence and on the proximate mechanisms or motivations, such as economic and social stress; and attitudes toward violence — all of which may underlie evolutionary fitness motivations. They authors conclude that understanding the evolutionary costs and benefits of intimate partner violence to partners and their families may aid institutional efforts to prevent it.
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Scientia Professor Rob Brooks is Director of the Evolution & Ecology Research Centre at the University of New South Wales
The causes of intimate partner violence are often only discussed in terms of the societal beliefs, norms and structures that support or erode violent behaviour. But what makes some individuals more likely than another to be violent toward an intimate partner? Stieglitz and colleagues, after careful field study among the Tsimané of Bolivia, show that individual men who favour controlling roles in their relationships tend to be violent toward their wives, but male aggression toward other men, and witnessing violent behaviour of their own parents, did not raise the chance of intimate partner violence.
To what end, then, would men be controlling? The evidence shows that couples in which men are violent toward their partners tend to have more children in those years when violence occurs. This leads to what evolutionary biologists call an “ultimate” explanation – a reason why a harmful practice like spousal abuse may occur. Much of men’s violence is already known to entail preventing their partners from mating with other men. Men and women routinely disagree over when to have the next child, if at all. This paper suggests men may be violent in order to wrest control over child-bearing decisions from their wives. There is much in this type of explanation that needs to be taken seriously if we are to understand and combat intimate partner abuse in other societies, including our own
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