Barbujani Guido - Bertorelle Giorgio - Genetics and the population history of Europe


Authors : Barbujani Guido - Bertorelle Giorgio
Title : Genetics and the population history of Europe
Year : 2001

Link download : Barbujani_Guido_-_Bertorelle_Giorgio_-_Genetics_and_the_population_history_of_Europe.zip

Analysis of genetic variation among modern individuals is providing insight into prehistoric events. Comparisons of levels and patterns of genetic diversity with the predictions of models based on archeological evidence suggest that the spread of early farmers from the Levant was probably the main episode in the European population history, but that both older and more recent processes have left recognizable traces in the current gene pool. Where do the genes of the Europeans come from? A good, but trivial, answer is: From Africa, like everybody else’s genes. Paleontologists agree that the long-term human ancestors, a million years ago or so, dwelt in Africa. There is disagreement, however, about what happened after archaic presapiens humans (Homo erectus) spread over much of the Old World. The anatomically archaic populations of Europe, Northeastern Asia, and Southeastern Asia may have gradually evolved into the modern Homo sapiens sapiens populations inhabiting, respectively, Western Eurasia, East Asia, and Australia; this is the multiregional theory of human evolution. On the contrary, the Out-of-Africa theory regards all modern populations as descended from an anatomically modern group that dispersed from Africa less than 200,000 years ago and replaced archaic populations. Discussing the relative merits of the two models would be out of place here, but the multiregional model proposes that the Neandertal people are the ancestors of contemporary Europeans. Conversely, we now know that the mitochondrial sequences of Neandertals differed sharply from modern European sequences, and in fact, from all modern human sequences. It is more than likely, then, that the Neandertal people left no modern descendants. If there was no Neandertal contribution to the contemporary gene pool, European gene diversity must reflect some combination of the demographic phenomena occurring after Homo sapiens sapiens colonized the continent. However, these phenomena acted upon genetic variation that accumulated both after and before Europe was colonized, because there is no reason to imagine that the first Europeans were all genetically identical. The distinction between histories of populations (which is what this paper is about) and histories of molecules (which are simpler to reconstruct, but are not the same thing) has sometimes been overlooked; we shall come back to it later. As for the European population history, the presence of Homo sapiens sapiens is first documented around 40,000 years ago. But which fraction of the modern European gene pool is derived from these first colonizers, and how much, instead, from more recent immigrants ? ...

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