Evidence for a Common Origin of Blacksmiths and Cultivators in the Ethiopian Ari within the Last 4500 Years: Lessons for Clustering-Based Inference.
The Ari peoples of Ethiopia are comprised of different occupational groups that can be distinguished genetically, with Ari Cultivators and the socially marginalised Ari Blacksmiths recently shown to have a similar level of genetic differentiation between them (FST ≈ 0.023 - 0.04) as that observed among multiple ethnic groups sampled throughout Ethiopia. Anthropologists have proposed two competing theories to explain the origins of the Ari Blacksmiths as (i) remnants of a population that inhabited Ethiopia prior to the arrival of agriculturists (e.g. Cultivators), or (ii) relatively recently related to the Cultivators but presently marginalized in the community due to their trade. Two recent studies by different groups analysed genome-wide DNA from samples of Ari Blacksmiths and Cultivators and suggested that genetic patterns between the two groups were more consistent with model (i) and subsequent assimilation of the indigenous peoples into the expanding agriculturalist community. We analysed the same samples using approaches designed to attenuate signals of genetic differentiation that are attributable to allelic drift within a population. By doing so, we provide evidence that the genetic differences between Ari Blacksmiths and Cultivators can be entirely explained by bottleneck effects consistent with hypothesis (ii). This finding serves as both a cautionary tale about interpreting results from unsupervised clustering algorithms, and suggests that social constructions are contributing directly to genetic differentiation over a relatively short time period among previously genetically similar groups.
University College London Genetics Institute (UGI), University College London, London, United Kingdom; Centre for Mathematics and Physics in the Life Sciences and EXperimental Biology (CoMPLEX), University College London, London, United Kingdom.
Lucy
L
van Dorp
University College London Genetics Institute (UGI), University College London, London, United Kingdom; Schools of BioSciences and of Mathematics & Statistics, University of Melbourne, Melbourne, Australia.
David
D
Balding
Department of Statistics, University of Oxford, Oxford, United Kingdom.
Simon
S
Myers
The Wellcome Trust Sanger Institute, Hinxton, United Kingdom; Department of Archaeology and Anthropology, University of Cambridge, Cambridge, United Kingdom.
Luca
L
Pagani
The Wellcome Trust Sanger Institute, Hinxton, United Kingdom.
Chris
C
Tyler-Smith
Addis Ababa University, Addis Ababa, Ethiopia.
Endashaw
E
Bekele
Henry Stewart Group, London, United Kingdom.
Ayele
A
Tarekegn
Research Department of Genetics, Evolution and Environment, University College London, London, United Kingdom.
Mark G
MG
Thomas
Henry Stewart Group, London, United Kingdom.
Neil
N
Bradman
University College London Genetics Institute (UGI), University College London, London, United Kingdom.
Garrett
G
Hellenthal
D000483:Alleles; D016000:Cluster Analysis; D003469:Culture; D005002:Ethiopia; D005006:Ethnicity / Q000235:genetics*; D040961:Genetic Drift; D005826:Genetics, Medical; D006801:Humans