According to the culture of honor hypothesis, the high prevalence of homicide in the US South originates from the settlement of the region by herders from the fringes of Britain in the late 18 th century. Combining contemporary homicide data with historical Census data, this paper confirms that Scot or Scots-Irish settlements are associated with higher homicide today, but only in the South. Using different proxies for institutional quality, I find that the Scots-Irish culture of honor only persisted where institutional quality was low. The interpretation is that the culture of honor, a private justice system, persisted in the South as an adaptive behavior to weak institutions. The effect is more pronounced where herding was more prevalent. It is confined to white offenders and to specific homicides that seem to aim at the defense of one's reputation. By contrast, the culture of honor deters violent crime against women. The culture of honor was transmitted to subsequent generations, but, again, only where formal institutions were weak. Evidence also suggests that the Scots-Irish culture of honor continues to adapt: it has been slowly fading over time.