African Origins The modern human originated in Africa and subsequently spread across the globe. However, the genetic relationships among the diverse populations on the African continent have been unclear. Tishkoff et al. (p. 1035; see the cover, published online 30 April) provide a detailed genetic analysis of most major groups of African populations. The findings suggest that Africans represent 14 ancestral populations. Populations tend to be of mixed ancestry which documents historical migrations. The data mainly support but sometimes challenge proposed relationships between groups of self-identified ethnicity previously hypothesized on the basis of linguistic studies. The authors also examined populations of African Americans and individuals of mixed ancestry from Cape Town, documenting the variation and origins of admixture within these groups.

To investigate associations between genetic, linguistic, and geographic variation in Africa, we type 50 Y chromosome SNPs in 1122 individuals from 40 populations representing African geographic and linguistic diversity. We compare these patterns of variation with those that emerge from a similar analysis of published mtDNA HVS1 sequences from 1918 individuals from 39 African populations. For the Y chromosome, Mantel tests reveal a strong partial correlation between genetic and linguistic distances (r ¼ 0.33, P ¼ 0.001) and no correlation between genetic and geographic distances (r ¼ À0.08, P40.10). In contrast, mtDNA variation is weakly correlated with both language (r ¼ 0.16, P ¼ 0.046) and geography (r ¼ 0.17, P ¼ 0.035). AMOVA indicates that the amount of paternal among-group variation is much higher when populations are grouped by linguistics (U CT ¼ 0.21) than by geography (U CT ¼ 0.06). Levels of maternal genetic among-group variation are low for both linguistics and geography (U CT ¼ 0.03 and 0.04, respectively). When Bantu speakers are removed from these analyses, the correlation with linguistic variation disappears for the Y chromosome and strengthens for mtDNA. These data suggest that patterns of differentiation and gene flow in Africa have differed for men and women in the recent evolutionary past. We infer that sex-biased rates of admixture and/or language borrowing between expanding Bantu farmers and local hunter-gatherers played an important role in influencing patterns of genetic variation during the spread of African agriculture in the last 4000 years.

The evolution of languages provides a unique opportunity to study human population history. The origin of Semitic and the nature of dispersals by Semitic-speaking populations are of great importance to our understanding of the ancient history of the Middle East and Horn of Africa. Semitic populations are associated with the oldest written languages and urban civilizations in the region, which gave rise to some of the world's first major religious and literary traditions. In this study, we employ Bayesian computational phylogenetic techniques recently developed in evolutionary biology to analyse Semitic lexical data by modelling language evolution and explicitly testing alternative hypotheses of Semitic history. We implement a relaxed linguistic clock to date language divergences and use epigraphic evidence for the sampling dates of extinct Semitic languages to calibrate the rate of language evolution. Our statistical tests of alternative Semitic histories support an initial divergence of Akkadian from ancestral Semitic over competing hypotheses (e.g. an African origin of Semitic). We estimate an Early Bronze Age origin for Semitic approximately 5750 years ago in the Levant, and further propose that contemporary Ethiosemitic languages of Africa reflect a single introduction of early Ethiosemitic from southern Arabia approximately 2800 years ago.

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From various kinds of evidence it can now be argued that agriculture in Ethiopia and the Horn was quite ancient, originating as much as 7,000 or more years ago, and that its development owed nothing to South Arabian inspiration. Moreover, the inventions of grain cultivation in particular, both in Ethiopia and separately in the Near East, seem rooted in a single, still earlier subsistence invention of North-east Africa, the intensive utilization of wild grains, beginning probably by or before 13,000 b.c. The correlation of linguistic evidence with archaeology suggests that this food-collecting innovation may have been the work of early Afroasiatic-speaking communities and may have constituted the particular economic advantage which gave impetus to the first stages of Afroasiatic expansion into Ethiopia and the Horn, the Sahara and North Africa, and parts of the Near East.