More than 500,000 women in the U.S. report violent attacks from their male partners. Now researchers say they may know why: men are acting on an evolutionary impulse to keep their partners from having another man’s child. "There are very predictable circumstances in which violence occurs," said David Buss, a researcher at the University of Texas. "For instance, with the threat of sexual infidelity or the threat of relationship termination." Two separate studies have confirmed a link between domestic violence and the likelihood that the woman was carrying another man’s child. Critics, however, say the research makes assumptions, and warns that men could use the conclusion as an excuse for violence.