A review of the pattern and magnitude of nero–white mating in the US is presented from the time of the earliest arrival of negroes in the American colonies until the present, using historical, demographic, census and genetic evidence.
The relative magnitude of negro male–white female matings compared to the converse are analysed in view of the different genetic outcomes of these two types of mating for X-linked genes. Contrary to many strongly stated opinions it is conclued from the historical evidence that, even from the earliest days of slavery, negro male–white female matings were a significant proportion of all negro–white matings. Census and demographic evidence suggests that their frequency increased so that from the time of the Civil War on they have formed a majority of inter-racial matings.
Genetic evidence based on estimates of the amout of admixture of white genes in a number of negro populations is considered. Estimates of admixture for the X-linked genes G6PD, and those for colour blindness are as high or higher than those derived from comparable autosomal genes.
Some observations on the total magnitude of negro–white mating, on the phenomenon of passing and on the relative socio-economic status of those involved are also made.
The implication of the findings on these phenomena for investigations and hypotheses concerning differences in intelligence and intellectual abilites between the races, particulary spatial ability which is thought to be strongly influenced by a gene on the X chromosome, are considered.
It is concluded that some of the assumptions made in proposing hypotheses regarding the origin and distribution of these abilities in the American negro are at variance with genetic, historical and sociological findings.