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Several models for the origin of Homo sapiens sapiens have been proposed. The "multiregional origin" model suggests that there was no single origin for all modern humans (1, 2). After the radiation of Homo erectus from Africa into Europe and Asia 800,000 to 1.8 million years ago (3), there was a continuous transition among regional populations from H. erectus to H. sapiens. Such "parallel evolution" among geographically dispersed populations could have been achieved by considerable amounts of gene flow between populations (1, 2). By contras, the "out of Africa" model suggests that all non-African human populations descend from an anatomically modern H. sapiens ancestor that evolved in Africa approximately 100,000 to 200,000 years ago and then spread and diversified throughout the rest of the Earth, supplanting any Homo populations still present outside of Africa (1 4). Migration out of Africa may have occurred in a single or in multiple waves (5).
The best-known genetic evidence used to support the out of Africa hypothesis has come from studies of mitochondrial DNA (mtDNA) in which it was proposed that all modern mtDNA can be traced back through the maternal lineage to a single ancestor that existed in Africa between 100,000 and 300,000 years ago (6, 7). The analysis and interpretation of these data have continued to be debated (8). Recent mtDNA (9) and Y chromosome (10) studies support the original findings of a recent origin of all modern humans. We present data from the nuclear autosomal genome that strongly support the out of Africa model of human origins and provide a different and independent estimate, based on linkage disequilibrium, of the recency of the emigration from Africa.
Genetic Systems Studied
We studied alleles from two tightly linked markers, located ==9.8 kb apart, within noncoding regions of the CD4 gene on the 1 short arm of chromosome 12 (11-13) (Fig. 1).(All figures omitted) These polymorphic markers are of two types that evolve with differing rates. The first is a short tandem repeat polymorphism (STRP). This class of markers consists of tandemly repeated blocks of two to five nucleotides; STRPs often have multiple alleles (defined by the number of repeats) and moderate to high mutation rates (14). Many researchers consider them particularly useful as markers for reconstructing recent evolutionary...