Mixed Race Studies

Caucasian Genes in American Negroes

Science (1969-08-22)
Volume 165
pages 762-768
DOI: 10.1126/science.165.3895.762

T. Edward Reed, Professor of Zoology and Anthropology; Associate Professor of Paediatrics
University of Toronto, Toronto, Canada

Measurement of non-African ancestry is difficult, but it is worthwhile for several genetic reasons.

It is very difficult to describe the genetic history of a large, defined human population in a meaningful way. As a result there have been few opportunities, at the population level, to study the consequences of known genetic events in the recent past of modem populations. The Negro population of the United States, however, is one of the exceptions to these generalizations. The American individual to whom the term Negro is applied is almost always a biracial hybrid. Usually between 2 and 50 percent of his genes are derived from Caucasian ancestors, and these genes were very probably received after 1700. While it is obviously of social and cultural importance to understand Negro hybridity, it is less obvious that there are several pertinent genetic reasons for wishing to know about the magnitude and nature of Caucasian ancestry in Negroes. Recent data, both genetic and historical, now make possible a better understanding of American Negro genetic history than has been possible heretofore. Here I review and criticize the published data on this subject, present new data, and interpret the genetic significance of the evidence.

In order to put the genetic data in proper context, I must first give a little of the history of American slavery. The first slaves were brought to what is now the United States in 1619. Importation of slaves before 1700 was negligible, however, but after that date it proceeded at a high rate for most of the 18th century. Importation became illegal after 1808 but in fact continued at a low rate for several more decades (1, 2). The total number of slaves brought into the United States was probably somewhat less than 400,000 (3). Charleston, South Carolina, was the most important port of entry, receiving 30 to 40 percent of the total number (4). More than 98 percent of the slaves came from a very extensive area of West Africa and west-central Africa-from Senegal to Angola-and, in these areas, from both coastal and inland regions. Shipping lists of ships that brought slaves to the United States-and to the West Indies, often to be sent later to the United States provide a fairly detailed picture of the geographic origins of the slaves and a less complete picture of their ethnic origins. Table 1 gives the approximate proportions of American slaves brought from the eight major slaving areas of Africa. The contribution from East Africa is seen to be negligible, whereas the area from Senegal to western Nigeria contributed about half the total and the region from eastern Nigeria to Angola contributed the other half. An earlier tabulation for entry at Charleston alone (5) is quite similar, except that the contribution from the Bight of Biafra is much less (0.021 as compared to 0.233) and that from “Angola” is appreciably greater (0.396 as compared to 0.245).

At some early point in American slavery, matings between slaves and Caucasians began to occur. Quantitative data are lacking, and we can say only that most of these matings occurred after 1700. Our concern here is the genetic consequences of the matings the introduction of Caucasian genes into the genome (or total complement of genetic material) of the American Negro. We could, in theory, estimate the Caucasian contribution to American Negro ancestry in a very simple way if certain strict criteria were met. In practice it is not possible to show that all these criteria are met, but this fact has not stopped geneticists, including myself, from making estimates…

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