Among the Tsimane 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 Tsimane 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 Tsimane 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.