Ancient DNA and deep population structure in sub-Saharan African foragers.

Multiple lines of genetic and archaeological evidence suggest that there were major demographic changes in the terminal Late Pleistocene epoch and early Holocene epoch of sub-Saharan Africa1-4. Inferences about this period are challenging to make because demographic shifts in the past 5,000 years have obscured the structures of more ancient populations3,5. Here we present genome-wide ancient DNA data for six individuals from eastern and south-central Africa spanning the past approximately 18,000 years (doubling the time depth of sub-Saharan African ancient DNA), increase the data quality for 15 previously published ancient individuals and analyse these alongside data from 13 other published ancient individuals. The ancestry of the individuals in our study area can be modelled as a geographically structured mixture of three highly divergent source populations, probably reflecting Pleistocene interactions around 80-20 thousand years ago, including deeply diverged eastern and southern African lineages, plus a previously unappreciated ubiquitous distribution of ancestry that occurs in highest proportion today in central African rainforest hunter-gatherers. Once established, this structure remained highly stable, with limited long-range gene flow. These results provide a new line of genetic evidence in support of hypotheses that have emerged from archaeological analyses but remain contested, suggesting increasing regionalization at the end of the Pleistocene epoch.

Middle Stone Age human teeth from Magubike rockshelter, Iringa Region, Tanzania.

In 2006, six isolated hominin teeth were excavated from Middle Stone Age (MSA) deposits at the Magubike rockshelter in southern Tanzania. They comprise two central incisors, one lateral incisor, one canine, one third premolar, and one fourth premolar. All are fully developed and come from the maxilla. None of the teeth are duplicated, so they may represent a single individual. While there is some evidence of post-depositional alteration, the morphology of these teeth clearly shares features with anatomically modern Homo sapiens. Both metric and non-metric traits are compared to those from other African and non-African dental remains. The degree of biological relatedness between eastern and southern African Stone Age hunter-gatherers has long been a subject of interest, and several characteristics of the Magubike teeth resemble those of the San of southern Africa. Another notable feature is that the three incisors are marked on the labial crown by scratches that are much coarser than microwear striations. These non-masticatory scratches on the Magubike teeth suggest that the use of the front teeth as tools included regularly repeated activities undertaken throughout the life of the individual. The exact age of these teeth is not clear as ESR and radiocarbon dates on associated snail shells give varying results, but a conservative estimate of their minimum age is 45,000 years.

Land Snail Shell Beads in the Sub-Saharan Archaeological Record: When, Where, and Why?

Shell beads are well established in the archaeological record of sub-Saharan Africa and appear as early as 75,000 BP; however, most research has focused on ostrich eggshell (OES) and various marine mollusc species. Beads made from various land snails shells (LSS), frequently described as Achatina, also appear to be widespread. Yet tracking their appearance and distribution is difficult because LSS beads are often intentionally or unintentionally lumped with OES beads, there are no directly dated examples, and bead reporting in general is highly variable in the archaeological literature. Nevertheless, Achatina and other potential cases of LSS beads are present at over 80 archaeological sites in at least eight countries, spanning the early Holocene to recent past. Here, we collate published cases and report on several more. We also present a new case from Magubike Rockshelter in southern Tanzania with the first directly dated LSS beads, which we use to illustrate methods for identifying LSS as a raw material. Despite the long history of OES bead production on the continent and the abundance of land snails available throughout the Pleistocene, LSS beads appear only in the late Holocene and are almost exclusively found in Iron Age contexts. We consider possible explanations for the late adoption of land snails as a raw material for beadmaking within the larger context of environmental, economic, and social processes in Holocene Africa. By highlighting the existence of these artifacts, we hope to facilitate more in-depth research on the timing, production, and distribution of LSS beads in African prehistory.

Les perles de coquillages sont bien établies dans les archives archéologiques de l'Afrique subsaharienne et apparaissent dès 75 000 BP, mais la plupart des recherches ont porté sur la coquille d'œuf d'autruche (OES) et diverses espèces de mollusques marins. Les perles fabriquées à partir de diverses coquilles d'escargots terrestres (LSS), souvent décrites comme Achatina, semblent également être répandues. Cependant, le suivi de leur apparence et de leur distribution est. difficile parce que les billes LSS sont souvent volontairement ou involontairement regroupées avec des billes OES, il n'y a pas d'exemples directement datés, et les rapports sur les perles en général sont très variables dans la littérature archéologique. Néanmoins, Achatina et d'autres cas potentiels de perles LSS sont présents sur plus de 80 sites archéologiques dans au moins huit pays, couvrant le début de l'Holocène à un passé récent. Ici, nous rassemblons les cas publiés et rapportons plusieurs autres cas. Nous présentons également un nouveau cas de Magubike Rockshelter dans le sud de la Tanzanie avec les premières perles LSS directement datées, que nous utilisons pour illustrer les méthodes d'identification du LSS comme matière première. Malgré la longue histoire de la production de perles d'OES sur le continent et l'abondance d'escargots terrestres disponibles tout au long du Pléistocène, les perles de LSS n'apparaissent qu'à la fin de l'Holocène et sont presque exclusivement trouvées dans des contextes de l'âge du fer. Nous considérons les explications possibles de l'adoption tardive des escargots terrestres en tant que matière première pour la fabrication de perles dans le contexte plus large des processus environnementaux, économiques et sociaux en Afrique de l'Holocène. En mettant en évidence l'existence de ces artefacts, nous espérons faciliter des recherches plus approfondies sur le calendrier, la production et la distribution des perles LSS dans la préhistoire africaine.