A new study in Nature reports on DNA obtained from six individuals in southeastern Africa who lived between 18-5 Kya (thousand years ago). A remarkable discovery, the study is one of the few that has been able to report on ancient DNA from a continent where warm and humid conditions are not conducive to the preservation of genetic material.
Lipson et al. (2022) reported radiocarbon dates as well as the complete genetic sequences of three Late Pleistocene (125–12 Kya) and three Early-Middle Holocene (11-5 Kya) individuals (six–four infants in total, two adults). , These six individuals were spread across five sites in eastern and south-central Africa: Tanzania, Malawi and Zambia, to be exact. These individuals ranged from 18 to 5, ‘doubling the timing depth of aDNA reported from sub-Saharan Africa.’ The practice was supplemented by previously published studies.
DNA was obtained from the petrous bone of the inner ear. Petrus is one of the hardest and densest bones in the body and preserves genetic material better than any other. a 2015 study even reported a 100-fold higher DNA yield from bone than any other. What has ancient DNA recovered from Petros helped shed light on? first farmer in turkeyin lineage Oceania and migrants Tanzaniaamong other things.
The researchers tapped into the insights offered by uniparental markers, that is, components of a person’s genetic material that come from only one parent. Uniparental markers are passed from one generation to the next ‘as is’ i.e. the set of traits are passed together as a ‘haplotype’. Therefore, univariate markers are extremely useful in the reconstruction of lineages through intensive time. Two of the most studied uniparental markers are the Y-chromosome, which follows a strict paternal inheritance, and mitochondrial DNA (mtDNA), which follows a strict maternal inheritance.
Based on the aforementioned univariate marker analysis, Lipson et al (2022) found that (a) samples from Kenya and Tanzania have haplotypes/haplogroups associated with East Africa; (b) the peoples of Malawi and Zambia have haplogroups associated with ‘certain ancient and present-day southern African peoples’, especially those still engaged in foraging; and (c) a person from Malawi and [maybe] Carries the haplogroup of an extant Central African forest dweller from Kenya. In the past, these haplogroup populations were much more widespread than they are today.
The researchers identified three distinct ancestors with a different geographic composition: one in East Africa, one in Southern Africa (not to be confused with South Africa) and another in the Central African rainforests. Genetic structures remained highly stable and localized compared to their geographic regions, and there was limited gene flow. These distinctive genetic structures have been masked by migration driven by the transition to sedentary agriculture in the past 5000 years, and even more recently by imperialism and changing socio-politics. Therefore, it is difficult to reconstruct demographic changes in the past from modern DNA alone and therefore, wherever possible, tap into ancient DNA.
Three lineages – Central African, Eastern and Southern – exist from southwestern Kenya to southeastern Zambia. 16 Until what, all three of these components were present in Malawi and, up to 7 what, in Tanzania. But ‘geographic proximity remains the strongest predictor of genetic similarity,’ and the three lineages exist in varying proportions.
This suggests that these groups were essentially 200 what separated but 80-50 what came into contact with each other. This led the authors to conclude that long-distance movements of people were probably rare in the Terminal Pleistocene/Holocene. This is also evidenced by signals in admixture analysis, which examines the degree of association between the two gene pools: admixture graphs showed high genetic affinity locally but not over long distances. For example, within three lineages, individuals in a group ‘showed additional allele sharing, even what might be expected from having similar ancestry ratios’.
These lineages, after 10 Kya, were probably brought together by fragmenting forests and expanding grasslands, leaving more room for people to roam.
The archaeological record sits well with the genetic evidence. Most of the records of material culture can be clearly identified in space and time (‘regionalisation’). Even linguistic data suggests a transition toward local interaction – to this day, communities in central, eastern and southern Africa speak languages belonging to different families (they share some similarities, certainly by way).
The researchers argue, ‘Our genetic results confirm that the trend of regionalization extends to human population structure, suggesting that a reduction in gene flow is accompanied by changes in behavior and possibly language.
The author is a Research Fellow at the Indian Institute of Science (IISc), Bengaluru and is a freelance science communicator. he tweets at @Criticism