Ein großes Problem genetischer Untersuchung scheinen schlicht die Anzahl der Proben zu sein und bestimmte, unterschiedliche Ansätze. Gerade in frühen historischen und prähistorischen Perioden sind die Proben einfach zu rar.
Über Mutationsraten hatten wir hier irgendwo, irgendwann mal gesprochen.
So verstehe ich die Probleme auch. Neben dem Probenmaterial scheinen in erster Linie -wie auch von Rena erwähnt- die Ausbreitungsmodelle und Annahmen über Variationsbreiten eine Rolle zu spielen, die Hypothese der "neolithic tracers" (sozusagen den genetischen Nachweis eines Ausbreitungsmodells Kleinasien -> Europa der neolithischen bzw. Agrarrevolution zu führen) zu widerlegen oder zu betätigen.
siehe auch:
"The Neolithic transition from hunting and gathering to farming and cattle breeding marks one of the most drastic cultural changes in European prehistory. Short stretches of ancient mitochondrial DNA (mtDNA) from skeletons of pre-Neolithic hunter-gatherers as well as early Neolithic farmers support the demic diffusion model where a migration of early farmers from the Near East and a replacement of pre-Neolithic hunter-gatherers are largely responsible for cultural innovation and changes in subsistence strategies during the Neolithic revolution in Europe. In order to test if a signal of population expansion is still present in modern European mitochondrial DNA, we analyzed a comprehensive dataset of 1,151 complete mtDNAs from present-day Europeans. Relying upon ancient DNA data from previous investigations, we identified mtDNA haplogroups that are typical for early farmers and hunter-gatherers, namely H and U respectively. Bayesian skyline coalescence estimates were then used on subsets of complete mtDNAs from modern populations to look for signals of past population expansions. Our analyses revealed a population expansion between 15,000 and 10,000 years before present (YBP) in mtDNAs typical for hunters and gatherers, with a decline between 10,000 and 5,000 YBP. These corresponded to an analogous population increase approximately 9,000 YBP for mtDNAs typical of early farmers. The observed changes over time suggest that the spread of agriculture in Europe involved the expansion of farming populations into Europe followed by the eventual assimilation of resident hunter-gatherers. Our data show that contemporary mtDNA datasets can be used to study ancient population history if only limited ancient genetic data is available."
http://www.ncbi.nlm.nih.gov/pubmed/22427842
Ergänzend die Zusammenfassung aus Caspari/Wolpoff, in: Smith/Ahern, The Origins of Modern Humans, S. 355ff.
"Neolithic Europe is a microcosm of the recent past and of the relation between past and present genetic diversity, a relationship that is important even if very significant amounts of current diversity are of recent origin. Neolithic farming reached Central Europe from the Levant by about 7,500 years ago. Genetic analysis suggests that European Neolithic populations were largely a consequence of population replacement and subsequent expansion (Fu et al., 2012): some 70% of the Neolithic settlements are of Levantine origin (Chihki et al., 2002), Neolithic hunter-gatherers of northern Europe have a genetic profile that is not often found in living populations of the region, continued gene flow between farmers from Mediterranean Europe and local and hunter-gatherer populations seems to have created current patterns of genetic variation there (Skoglund et al., 2012), and 82% of the mtDNA variants found in the earlier Central European hunter-gatherers are not found in Central Europe today (Bramanti et al., 2009). These replacements involved significant admixture with existing Europeans; “the clinal distributions of nuclear DNA and protein markers suggest that a directional expansion from the Levant is the main process reflected in the current genetic diversity” (Barbujani and Bertorelle, 2001: 23). Similar recent expansions and local replacements with mixture occurred in many places (Gignoux et al., 2011). The large population expansions of the Holocene were not simple in situ increases of all populations. In many, perhaps most, cases, few populations expanded at the expense of many others."