average 30% of their gene pool from European (White American) genes (28). This partial replacement took place over about 300 years of contact, and it is calculated that, if it was constant in time, there must have been about 3% of mixed unions per generation. Laws assured that the child of mixed parentage would be considered Black. Only individuals with a very low proportion of Black ancestry (or of skin color) would be able to “pass” as White. With gene flow continuing at that same rate, only about 30% of the original gene constitution would remain on average after 1,000 years since the beginning, and about 9% after 2,000 years (1).
Gene and language replacement can to some extent blur the congruence expected between the two types of evolution, but not completely. The accumulation of further genetic and linguistic data will facilitate the study of the relationship between the two evolutions, making it easier to use the genetic tree for predicting the history of linguistic evolution. Charles Darwin had precisely anticipated this development in his first book, The Origin of Species, published in 1859. But the opposite can also happen, and we look forward to linguistic data for ideas about still undetected genetic relationships. Above all we need an increase in genetic data, which modern molecular techniques such as microsatellite analysis and chip hybridization make possible and unusually powerful. The generation of a world collection of stored DNAs for distribution to scientists is the aim of the Human Genome Diversity Project, the feasibility of which is currently being investigated by the National Research Council and by the National Science Foundation.
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