The Bantu expansion
The Bantu are thought to have originated from the the area of Nigeria/Cameroon, and started their expansion East and South about 5,000 years ago (3,000 BC). They reached the equatorial rain forest 3500 years ago, entering what is now Uganda, 3000 years ago. It is people of this ancestry that comprised the bulk of the slaves transported across the Atlantic, and most black Americans can trace their ancestry to West and West-central Africa.
The success of the Bantu was to do with farming. In a pattern repeated the world over throughout history, the farming people expand relatively quickly into lands occupied by hunter gatherers, displacing them, and absorbing a small number of them into their population. Prior to 3000 BC the population of sub Saharan Africa looked like the Khoisan people. The Bantu underwent a recent, massive, population explosion and are now numerically superior. If you went back in time 5,000 years, they would only be a few hundred thousand Bantu people learning to farm on the Western side of Africa. Bantu speakers w number about 60 million, and most of of sub Saharan Africa now speaks some version of the Niger-Congo language family.
This was different to how farming spread in Europe. Although some new population arrived in Southern Europe, most of the old population remained, they simply adopted farming. This was not the case with the Bantu expansion. The neolithic hunter gatherers, although they implemented pastoralism, failed to implement agriculture and were mostly displaced. They are now marginalised to areas where agriculture is not possible, like deserts and scrub land. The Bantu brought their language with them, and their spread can be seen below. You can see how the original Khoisan people (palest brown) have been engulfed by the spread of the Bantu people (light brown).
The Bantu brought their cattle and goats with them, and finally carried the technology of iron into Southern Africa, iron arriving in Southern Africa about 400 AD. The exact date of iron working starting in Africa is unclear to say the best, but the first widely recognised smiths In sub Saharan Africa were the Nok people of Nigeria. There’s an interesting read called ‘Iron roads in Africa’ that claims multiple independent discoveries of iron working, but the evidence is open to criticism due to the common use of fossil charcoal, which can give a false age, and a poor standard of archaeology.
Igbo kids, Nigeria. Kikuyu woman, Kenya.
Boys, Mozambique. Ugandan children.
A sample of mitochondrial DNA (mtDNA) from the southeastern African population of Mozambique has been shown to have affinities with populations both to its north and south. From the north came sequences that may have been involved in the Bantu expansion (from western, through eastern, to southern Africa), such as members of haplogroups L3b, L3e1a and a subset of L1a. The dating of the major component of Mozambican mtDNAs, the subset L2a of haplogroup L2, displayed an age range compatible with the Bantu expansion. The southern influence was traced by the presence of sequence types from haplogroup L1d, a probable relict of Khoisan-speaking populations that inhabited the region prior to their displacement by the Bantu-speaking incomers. Within historicaltimes, the forced displacement of Mozambicans as part of the slave trade, mainly documented as being to the Americas, generated a differential input of eastern African sequences into the mtDNA pools of the Americas and of Europe, as testified to by the greater number of sequence matches between Mozambique and the Americas, compared to those between Mozambique and Europe
The extent of genetic differentiation between seven South African Bantu-speaking groups (Zulu, Xhosa, Tsonga/Shangaan, Southern Sotho, Pedi, Tswana, and Venda) was assessed from coancestry coefficients (FST) estimated from autosomal serogenetic, DNA, and Y-chromosome DNA haplotypes. The overall FST obtained from the autosomal data was 0.002, and that from the Y chromosome data was 0.014. The genetic relationships between groups examined were inferred from their cluster affinities in phylogenetic trees constructed from the genetic distances between them. Both autosomaland Y-chromosome DNA studies reveal that 6 of the 7 South African Bantu-speaking groups cluster according to their linguistic groupings, the exception being the Tsonga, who do not cluster with other Nguni language speakers, but rather with the Venda who live close to them. This suggests that the invading Shangaan-speakers, whose Nguni language was adopted by the Tsonga, did not have a major effect on the Tsonga gene pool, and that gene flow from the Venda into the Tsongamay have been considerable. Genetic distances were found to correlate with geographic distances between the regions where each group’s apparent population density is the highest. Linguistic distances were also found to correlate with genetic distances, but linguistic and geographic distances showed no correlation. Together, these results suggest that linguistic and some genetic differentiation took place before the groups (or their forerunners) reached their present-day locations, and that further genetic change occurred after their arrival.
American journal of physical anthropology
Insights into the western Bantu dispersal: mtDNA lineage analysis in Angola
Africa is the homeland of humankind and it is known to harbour the highest levels of human genetic diversity. However, many continental regions, especially in the sub-Saharan side, still remain largely uncharacterized(i.e. southwest and centralAfrica). Here, we examine the mitochondrial DNA (mtDNA) variation in a sample from Angola. The two mtDNA hypervariable segments as well as the 9-bp tandem repeat on the COII/tRNA(lys) intergenic region have allowed us to allocate mtDNAs to common African haplogroups. Angola lies in the southern end of the putative western branch of the Bantu expansion, where it metthe local Khoisan populations. Angolan mtDNA lineages show basically a Bantu substrate with no traces of Khoisan lineages. Roughly, more than half of the southwestern mtDNApool can be assigned to west Africa, approximately 25% to central Africa and a significant 16% to east Africa, which points to the western gene pool having contributed most to the mtDNA lineages in Angola. We have also detected signals of extensive gene flow from southeast Africa. Our results suggest that eastern and western Bantu expansion routes were not independent from each other, and were connected south of the rainforest and along the southern African savannah. In agreement with historical documentation, the analysis also showed that the Angola mtDNA genetic pool shows affinities with the African lineages from Brazil, the main American destination of the slaves from Angola, although not all lineages in Brazil can be accounted for by the Angolan mtDNA pool.
A very technical paper, as a pdf. document.
An alternative explanation, not considered by the authors is that mtDNA, known to be involved in energy production, is subject to strong selection in different natural environments, and therefore, there may have been selection against Eurasian mtDNAafter its initial introduction into the population.
American Journal of Physical Anthropology
Early View (Articles online in advance of print)
MtDNA variation in North Cameroon: Lack of asian lineages and implications for back migration from Asia to sub-Saharan Africa
Valentina Coia et al.
It’s quite interesting that an ancient European Berber mitochondrial DNA lineage (U6) has been carried South by the Bantu expansion. This probably spread South into the founder Bantu population during the last Saharan pluvial period, about 12,000 to 4,000 years ago, when the Sahara was a grassland.