The authors examine the ecological foundations of the thesis of a "code of honor" as an explanation for southern homicide. Specifically, they consider the effects of indicators of ethnic groups that migrated from herding economies (the Scotch-Irish), cattle and pig herding, and the relative importance of agricultural production across different areas in the Old South. Using county-level data on argument-related White male homicide offenders (1983 to 1998) from the Federal Bureau of Investigation's Supplementary Homicide Reports, the authors observe the theoretically expected positive interaction between the proxy measure of the presence of Scotch-Irish communities, namely, the percentage of churches that were Presbyterian in 1850, and the number of cattle and pigs per capita in 1850. They also find a negative effect of an index of crop production in 1850 on argument-related offending. The overall pattern of these findings is highly consistent with the herding thesis advanced by Nisbett and Cohen. (Contains 15 notes, 1 table and 1 figure.)