The peopling of the African continent and the diaspora into the new world

Abstract

Africa is the birthplace of anatomically modern humans, and is the geographic origin of human migration across the globe within the last 100,000 years. The history of African populations has consisted of a number of demographic events that have influenced patterns of genetic and phenotypic variation across the continent. With the increasing amount of genomic data and corresponding developments in computational methods, researchers are able to explore long-standing evolutionary questions, expanding our understanding of human history within and outside of Africa. This review will summarize some of the recent findings regarding African demographic history, including the African Diaspora, and will briefly explore their implications for disease susceptibility in populations of African descent.

Figure 1

The geography of major Homo sapiens (H. sapiens) fossil sites. This map, adapted from [8], illustrates the geographic distribution of sites in Africa where early archaic, late archaic and modern H. sapiens have been found. The labeled sites are the names of fossil remains that have been designated as modern H. sapiens. A more detailed description of the ‘modern’ features of these fossils is given in Table 1.

Figure 2

A model of divergence and admixture in Africa. This figure illustrates some of the proposed divergence events in Africa, for example the divergence of San Khoesan-speaking hunter-gatherers (HGs) ancestors >100 kya [25,29], and the differentiation of the ancestor of Pygmy HGs from a non-Pygmy population ~60–70 kya [30,33,34]. Genetic substructure has also been detected among western Pygmies who also show evidence for admixture with Central African Bantu-speaking agriculturalists [,,,–93]. Solid lines indicate gene flow between the ancestors of modern populations, and the dashed arrows indicate archaic introgression. Studies have reported evidence for archaic introgression from an unknown archaic species into several populations including the Biaka Pygmy and the Yoruba [46,51,53] shown here by the dashed arrows and question marks (which indicate that additional studies of African populations are needed to understand the extent and timing of archaic admixture in Africa). Lastly, the decreasing intensity of the blue color within the modern human lineage represents the loss of diversity as AMHs migrated across the globe from Africa within the last 100,000 years.

Figure 3

The geography of major linguistic families and of historic migration events in Africa. Africa not only has the highest levels of genetic diversity, but a considerable amount of linguistic diversity is also found across the continent. Currently, more than 2000 distinct languages exist in Africa, representing about a third of the world’s languages, which can be classified into four major linguistic families: (1) Niger-Kordofanian is a family of languages (including Bantu) spoken primarily by agriculturalists across a wide geographic region in Africa; (2) Nilo-Saharan languages are spoken predominantly by pastoralists in Central and East Africa; (3) Afroasiatic languages are spoken mainly by pastoralists and agropastoralists in East and North Africa; (4) Khoesan, which consists of languages with click consonants, is spoken primarily by hunter-gatherer populations in East and South Africa. This map, adapted from [1,2], also shows a number of key migration events, most notably the geographic expansion of Bantu Niger-Kordofanian-speakers across Africa from a homeland near the Nigeria/Cameroon border, as well as the general geographic regions (shown here by the red circles) where enslaved Africans were transported from Africa to the New World based on historical records.