Abstract

BackgroundThe modern human colonization of Eurasia and Australia is mostly explained by a single-out-of-Africa exit following a southern coastal route throughout Arabia and India. However, dispersal across the Levant would better explain the introgression with Neanderthals, and more than one exit would fit better with the different ancient genomic components discovered in indigenous Australians and in ancient Europeans. The existence of an additional Northern route used by modern humans to reach Australia was previously deduced from the phylogeography of mtDNA macrohaplogroup N. Here, we present new mtDNA data and new multidisciplinary information that add more support to this northern route.MethodsMtDNA hypervariable segments and haplogroup diagnostic coding positions were analyzed in 2,278 Saudi Arabs, from which 1,725 are new samples. Besides, we used 623 published mtDNA genomes belonging to macrohaplogroup N, but not R, to build updated phylogenetic trees to calculate their coalescence ages, and more than 70,000 partial mtDNA sequences were screened to establish their respective geographic ranges.ResultsThe Saudi mtDNA profile confirms the absence of autochthonous mtDNA lineages in Arabia with coalescence ages deep enough to support population continuity in the region since the out-of-Africa episode. In contrast to Australia, where N(xR) haplogroups are found in high frequency and with deep coalescence ages, there are not autochthonous N(xR) lineages in India nor N(xR) branches with coalescence ages as deep as those found in Australia. These patterns are at odds with the supposition that Australian colonizers harboring N(xR) lineages used a route involving India as a stage. The most ancient N(xR) lineages in Eurasia are found in China, and inconsistently with the coastal route, N(xR) haplogroups with the southernmost geographical range have all more recent radiations than the Australians.ConclusionsApart from a single migration event via a southern route, phylogeny and phylogeography of N(xR) lineages support that people carrying mtDNA N lineages could have reach Australia following a northern route through Asia. Data from other disciplines also support this scenario.

Highlights

  • There is wide interdisciplinary agreement on the African origin of Anatomically Modern Humans (AMH) around 200 thousand years ago, and on the idea that they expanded out of that continent to colonize the rest of the world replacing, with only minor genetic exchanges, the indigenous hominids already present in Eurasia [1,2]

  • The existence of an additional Northern route used by modern humans to reach Australia was previously deduced from the phylogeography of mitochondrial DNA (mtDNA) macrohaplogroup N

  • The Saudi mtDNA profile confirms the absence of autochthonous mtDNA lineages in Arabia with coalescence ages deep enough to support population continuity in the region since the out-of-Africa episode

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Summary

Introduction

There is wide interdisciplinary agreement on the African origin of Anatomically Modern Humans (AMH) around 200 thousand years ago (kya), and on the idea that they expanded out of that continent to colonize the rest of the world replacing, with only minor genetic exchanges, the indigenous hominids already present in Eurasia [1,2]. Based mainly on the coalescence age of mitochondrial DNA (mtDNA) L3 lineages, most geneticists propose a temporal window of 60–70 kya as the time for the exit, coinciding with the early Last Glacial stage (MIS 4). This hypothesis involves a southern route to Arabia across the Bab al Mandab strait, which, at that time, would have presented a very low sea level [3,4,5,6]. We present new mtDNA data and new multidisciplinary information that add more support to this northern route

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