First DNA extracted from an ancient African skeleton shows widespread mixing with Eurasians
Published by M. Gallego Llorente et al.
Article in Science
What was the research project?
Previously, genomes of ancient civilizations in various regions had been sequenced, excluding Africa. Ancient genomes tend to be available in more Arctic regions where the DNA is preserved for longer periods. Africa, being the birthplace of humanity, would provide key information into the origin of our species. In October, 2015 a paper was published by BLANK featuring the first sequenced genome from prehistoric Africa. The genome was that of an African man found in the Mota Cave of Ethiopia. The man was named Mota, after the cave, and estimated to have died about 4500 years ago using radiocarbon dating. The age of Mota is important because it differentiates any potential Eurasian ancestry from the Eurasian backflow shown to occur around 3000 years ago into southern and eastern Africa (Lipson et al. 2014).
Generally, prehistoric Africa is viewed as an area where people traveled out of, rather than into. Evidence of any Eurasian immigration back into Africa at earlier points in history would be of much importance to studying overall genetic diversity and for the understanding of ancient migration patterns. Sampling for DNA was done using part of the temporal bone in the skull.
Much of the Mota’s genome matched that of a group in Ethiopia (the Ari); however, he also possessed DNA consistent with that of farmers found in prehistoric Germany. This German DNA is believed to have been obtained by both German and African populations from Middle Eastern genomes. Evidence overall points to descendants of farmers 8,000 years ago migrating into North Africa.
Were they testing a hypothesis or doing discovery science?
They were doing discovery science by attempting to be the first to find and sequence the genome of a prehistoric African man. There was no hypothesis involved because they did not know what clues would be found in the genome. The project was intended to use the ancient Mota genome to "disentangle the effects of recent population movement into Africa," but know predictions were made before analysis (Llorente et al. 2015).
What genomic technology was used in the project?
Principal component analysis was used to find any sort of linear correlation between many sets of regional genomic data. Allowing this statistical analysis to sort the data in such a fashion allows for identification of closely related genomic groups within a larger population of various genomes. In this case, PCA was used to show the close genomic relationship of Mota to the East African population of the Ari (Figure 1).
Figure 1: PCA showing close relationship between Ari and Mota (A), Outgroup analysis visualizing genetic drift both separated by groups (B) and geographically (C) (Llorente et al. 2015)
Additionally, outgroup f3 analysis using southern African genomes as an outgroup was used to further show the close relationship of the Mota genome to that of the Ari. outgroup analysis was also used to determine from where the West Eurasian component in Mota's genome was donated from. (Figure 2)
Figure 2: Outgroup analysis indicating most likely sources of Eurasian DNA and the geographic reaching of that component. (Llorente et al., 2015)
What was the take home message?
There is now evidence of immigration of Middle Eastern farmers into Africa thanks to new genomic evidence from a prehistoric African man. Generally, the belief has been entirely an "out-of-Africa" model for the migration of humans prehistorically. This evidence still supports that model, but provides an interesting wrinkle to the story. Humans migrated out of Africa into the Middle East and Europe, but years later some Middle Easterners migrated back into Africa.
Ultimately, this study is
a testament to the importance of whole genome analysis for the study of
lineage and human history. Using DNA from prehistoric humans gives
scientists an opportunity for further understanding of the migration
patterns of early humans. Understanding these migration patterns provides
more context for the characteristics within regional genomes and how those
ultimately came about.
What is your evaluation of the project?
Overall, the project is well done and extremely important for our understanding of ancient migration. I feel that the overall collection of data and analysis has convinced me of their conclusion. The project as a whole, other than finding and sampling the DNA of a 4,500 year old man, was actually rather simplistic and only featured a few specific analyses of the DNA relative to the questions being asked.
Moving forward, this project can be useful for adjusting the understanding of ancient human migration in and out of Africa and provides some evidence for another previously unknown migration into Africa many years before anticipated. Scientists are no longer held to only using contemporary African genomes for the study of genomic diversity and expansion of the modern human. Mota gives scientists a new baseline to make genomics inferences regarding human migration over a longer time period.
However, I do believe that this is a field of study that may require more data and more individuals. The problem is that it is extremely challenging to find these individuals that lived in Ancient Africa. The study will always likely be limited by this, so future researchers should consider that when reconstructing explanation for human diversity and migration. However, the data is compelling regardless of it only being one human sample, and it seems to provide strong evidence of this ancient Eurasian migration to Africa.
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