There is a centuries old debate about violence between people - is it something we're born with, or a product of our environment? Understanding the causes of violence is important if we want to try and reduce it, and so there have been hundreds of social experiments trying to establish this. But this week, some scientists have taken a different approach, and looked across all mammals for answers, and found that throughout human ancestry, we have been becoming progressively more violent. Laura Brooks spoke to Professor Mark Pagel of the University of Reading, who had been looking into the study.