The relationship between race and crime has been an area of study for criminologists since the emergence of anthropological criminology in the late 19th century. Cesare Lombroso, founder of the Italian school of criminology, argued that criminal behavior was the product of biological factors, including race. He was among the first criminologists to claim a direct link between race and crime. This biological perspective, sometimes seen as racist and increasingly unpopular, was criticized by early 20th century scholars, including Frances Kellor, Johan Thorsten Sellin and William Du Bois, who argued that other circumstances, such as social and economic conditions, were the central factors which led to criminal behavior, regardless of race. Du Bois traced the causes of the disproportional representation of Blacks in the criminal justice system back to the improperly handled emancipation of Black slaves in general and the convict leasing program in particular. In 1901, he wrote: