 A specialist in world history and African history, his current research addresses global historiography, early human history, migration in world history, the African diaspora, and the demography of African slavery.He was educated at the California Institute of Technology (BS in Chemistry, 1963) and the University of Wisconsin–Madison (MS in History and Economics, PhD in History 1969).He was trained as a specialist in the economic history of Africa, and went on to explore demographic, social, and cultural patterns in Africa and the African diaspora.