Christopher Ehret

The Genetic Structure and History of Africans and African Americans

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. A genetic study illuminates population history, as well as the relationships among and the origin of major language families. Africa is the source of all modern humans, but characterization of genetic variation and of relationships among populations across the continent has been enigmatic. We studied 121 African populations, four African American populations, and 60 non-African populations for patterns of variation at 1327 nuclear microsatellite and insertion/deletion markers. We identified 14 ancestral population clusters in Africa that correlate with self-described ethnicity and shared cultural and/or linguistic properties. We observed high levels of mixed ancestry in most populations, reflecting historical migration events across the continent. Our data also provide evidence for shared ancestry among geographically diverse hunter-gatherer populations (Khoesan speakers and Pygmies). The ancestry of African Americans is predominantly from Niger-Kordofanian (~71%), European (~13%), and other African (~8%) populations, although admixture levels varied considerably among individuals. This study helps tease apart the complex evolutionary history of Africans and African Americans, aiding both anthropological and genetic epidemiologic studies.

Contrasting patterns of Y chromosome and mtDNA variation in Africa: Evidence for sex-biased demographic processes

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=0.33, P=0.001) and no correlation between genetic and geographic distances (r=−0.08, P>0.10). In contrast, mtDNA variation is weakly correlated with both language (r=0.16, P=0.046) and geography (r=0.17, P=0.035). AMOVA indicates that the amount of paternal among-group variation is much higher when populations are grouped by linguistics (ΦCT=0.21) than by geography (ΦCT=0.06). Levels of maternal genetic among-group variation are low for both linguistics and geography (ΦCT=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.

Bayesian phylogenetic analysis of Semitic languages identifies an Early Bronze Age origin of Semitic in the Near East

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 worlds 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.

Linguistic evidence and its correlation with archaeology

Abstract Linguistic evidence has long been applied to problems of historical reconstruction; and, in particular, considerable effort has been expended in the search for correlations between archeo‐logical and linguistic sources for history. Nevertheless, linguistic sources have remained, for the most part, insufficiently utilized. Historical inferences can be made from the kinds of evidence which inhere in the data of language relationships and from toponymy; and both these kinds of data have received extensive use. But historical inferences, of much more detailed and more complex kinds, can be made from the diachronic analysis of adopted elements, specifically word‐borrowings, in languages; and this sort of study has only too frequently not been undertaken. Applied in conjunction, the two categories of linguistic evidence reveal the probable approximate locations through time of, the relative historical sequence of interactions between, and the sequence of developments within, the groups of societies fro...

On the Antiquity of Agriculture in Ethiopia

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.

Cattle-Keeping and Milking in Eastern and Southern African History: The Linguistic Evidence

Cattle have been known in northern East Africa for a long time. A single people initiated the spread of cattle farther south through southern East Africa, and partly into southern Africa, at a time prior to the expansion of Bantu-speakers into these regions. This spread was not accompanied by knowledge of milking. The milking of cattle, although very likely practised by some northern East African peoples since a very early period, diffused to Bantu peoples after their advance into eastern and southern Africa was well under way. The practice was probably borrowed from Southern Cushites first by Bantu in northern Tanganyika and through them transmitted to the rest of the eastern and southern Bantu.

Bantu history: Big advance, although with a chronological contradiction

In their article “Bantu expansion shows that habitat alters the route and pace of human dispersals,” Grollemund et al. (1) have accomplished more than just their stated intention: to identify the role of habitat in channeling the directions of the early Bantu farming settlement of the African equatorial rainforest. What is most important is that the authors essentially bring closure to four decades of debate, at least with respect to the geography of the early stages and routes of expansion of Bantu speakers across vast portions of the African continent. On the geography of this spread, their findings confirm the validity of a particular line of linguistic and historical argument initiated more than 40 y ago (2) and developed and elaborated upon by a succession of investigations in the intervening years (3⇓–5). Grollemund et al. (1) rule out, as did those other studies, the idea that the ancestral speakers of the Eastern Bantu branch might have reached eastern Africa by a circuitous route around the north side of …

An African Classical Age: Eastern and Southern Africa in World History 1000 BC to AD 400

Setting the historical stage the formative eras of classical Mashariki society mapping the mosaics of cultural interaction regional trends and developments East Africa in the later classical age, to A.D. 400 southeastern Africa in the later classical age, to A.D. 400 social and economic transformation in the later classical age, 300 B.C. to A.D. 400. Appendixes: adjunct tables of evidence supplementary tables of evidence.