(..) This group** from the University of Toulouse, INSERM, the University of Bordeaux, University of Indonesia, the Max Plank Institute for Evolutionary Anthropology, Institut genomique, Centre Nacional de Genotypage, University of Melbourne, and the Universite de la Rochelle, showed geographic stratification between ancestral African (mostly Bantu) and Asian (Austronesean) ancestors. Cultural, historical, linguistic, ethnographic, archeological, and genetic studies supports the conclusion that Madagascar residents have traits from both populations but the effects of settlement history are termed "contentious" by these authors. Various competing putative "founder" populations (including Arabic, Indian, Papuan, and/or Jewish populations as well as first settlers found only in legend, under names like "Vazimba," "Kimosy," and "Gola") have been posited as initial settlers. These researchers report an attempt to illuminate the ancestry of the Malagasy by a study of human genetics.
These results showed common Bantu and Austronesian descent for the population with what the authors termed "limited" paternal contributions from Europe and Middle Eastern populations. The admixture of African and Austronesian populations occurred "recently" (i.e., over the past millennium) but was gender-biased and heterogeneous, which reflected for these researchers independent colonization by the two groups. The results also indicated that detectable genetic structure can be imposed on human populations over a relatively brief time (~ a few centuries).
Using a "grid-based approach" the researchers performed a high-resolution genetic diversity study that included maternal and paternal lineages as well as genome-wide data from 257 villages and over 2,700 Malagasy individuals. Maternal inheritance patterns were interrogated using mitochondrial DNA and patterns of paternity assayed using Y chromosomal sequences. Non-gender specific relationships were assessed through 2.5 million SNPs. Mitochondrial DNA analyses showed maternal inheritance from either African or East Asian origins (with one unique Madagascar variant termed M23) in roughly equal amounts, with no evidence of maternal gene flow from Europe or the Middle East. The M23 variant shows evidence of recent (within 900-1500 years) origin. Y chromosomal sequences, in contrast are much more prevalent from African origins (70.7% Africa:20.7% East Asia); the authors hypothesize that the remainder may reflect Muslim influences, with evidence of but little European ancestry.
Admixture assessments support Southeast Asian (Indonesian) and East African source populations for the Malagasy admixture. These results provide the frequency of the African component to be ~59%, the Asian component frequency to be ~37%, and the Western European component to have a frequency of about 4% (albeit with considerable variation, e.g., African ancestry can range from ~26% to almost 93%). Similar results were obtained when the frequency of chromosomal fragments shared with other populations were compared to the Malagasy population (finding the closest link to Asian populations from south Borneo, and excluding Indian, Somali, and Ethiopian populations, although the analysis was sensitive in one individual to detect French Basque ancestry). The split with ancestral Asian populations either occurred ~2,500 years ago or by slower divergence between ~2,000-3,000 years ago, while divergence with Bantu populations occurred more recently (~1,500 years ago).
There were also significant differences in geographic distribution between descendants of these ancestral populations. Maternal African lineages were found predominantly in north Madagascar, with material Asian lineages found in central and southern Madagascar (from mtDNA analyses). Paternal lineages were generally much lower overall for Asian descendants (~30% in central Madagascar) based on Y chromosome analyses. Genome-wide analyses showed "highlanders" had predominantly Asian ancestry (~65%) while coastal inhabitants had predominantly (~65%) African ancestry; these results depended greatly on the method of performing the analyses which affected the granularity of the geographic correlates. Finally, assessing admixture patterns indicated that the genetic results are consistent with single intermixing event (500-900 years ago) for all but one geographic area, which may have seen a first event 28 generations ago and a second one only 4 generations ago. These researchers also found evidence of at least one population bottleneck, where the number of individuals dropped to a few hundred people about 1,000-800 years ago.
These results are represented pictorially in the paper:
Figure 2
In view of the current political climate, the eloquent opening of the paper deserves attention:
Ancient long-distance voyaging between continents stimulates the imagination, raises questions about the circumstances surrounding such voyages, and reminds us that globalization is not a recent phenomenon. Moreover, populations which thereby come into contact can exchange genes, goods, ideas and technologies.
* Marc Haber, Claude Doumet-Serhal, Christiana Scheib, Yali Xue, Petr Danecek, Massimo Mezzavilla, Sonia Youhanna, Rui Martiniano, Javier Prado-Martinez, Michał Szpak, Elizabeth Matisoo-Smith, Holger Schutkowski, Richard Mikulski, Pierre Zalloua, Toomas Kivisild, Chris Tyler-Smith
** Denis Pierrona, Margit Heiskea, Harilanto Razafindrazakaa, Ignace Rakotob, Nelly Rabetokotanyb, Bodo Ravololomangab, Lucien M.-A. Rakotozafyb, Mireille Mialy Rakotomalalab, Michel Razafiarivonyb, Bako Rasoarifetrab, Miakabola Andriamampianina Raharijesyb, Lolona Razafindralambob, Ramilisoninab, Fulgence Fanonyb, Sendra Lejamblec, Olivier Thomasc, Ahmed Mohamed Abdallahc, Christophe Rocherc,, Amal Arachichec, Laure Tonasoa, Veronica Pereda-lotha, Stéphanie Schiavinatoa, Nicolas Brucatoa, Francois-Xavier Ricauta, Pradiptajati Kusumaa,d,e, Herawati Sudoyod,e, Shengyu Nif, Anne Bolandg, Jean-Francois Deleuzeg, Philippe Beaujardh, Philippe Grangei, Sander Adelaarj, Mark Stonekingf, Jean-Aimé Rakotoarisoab, Chantal Radimilahy, and Thierry Letelliera
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