The book focuses on the role of both biological and behavioural factors in the fertility, and specific patterns of health and disease, of minority populations living in developed and less developed countries. The importance of marriages contracted between close relatives is stressed, as over 900 million people inhabit countries where 20 to 50 per cent of marriages are inbred. Past, present and future trends in population mixing are evaluated, with special consideration of their effects on the health of minorities.