Late hunter-gatherers and early farmers in iberiaan ancient dna and isotope perspective

Resumen

The transition from foraging to farming is one of the most drastic shifts visible in the archaeological record. In Europe, the so-called ‘Meso-Neolithic transition follows a chronological gradient from the origin in the Near East to Western Europe, following two main routes: the Danubian inland route and the Mediterranean route. In this sense, the Iberian Peninsula, located in the southwestern part of Europe is a key region to study the transition from foraging to farming in the most distant end of the expansion. Previous studies have pointed out that the previous local hunter-gatherers were genetically very distinct from the newly arriving farmers. Mitochondrial DNA analysis showed an almost complete replacement of the hunter-gatherer mitochondrial haplogroups at the beginning of the Neolithic. Analysis of autosomal genome-wide data confirms that most of the genetic ancestry of farmers is derived directly from Anatolian Neolithic groups with a limited admixture of hunter-gatherer ancestry along the routes of expansion. In terms of subsistence, it is also possible to track a substantial change in the lifestyle of the first Neolithic communities in comparison with previous hunter-gatherer groups. The new food producing economy caused a decrease in dietary diversity. We observe a systematic abandonment/negligence/disregard of marine resources albeit a persistence of hunting, and usually combined with management of domestic livestock and crops. Farming also included a variety of husbandry strategies, such as feeding animals with special fodder or human waste products, the use of enclosures for animal keeping, transhumance and the use of natural fertilizers on crops. The analysis of stable isotope analysis (carbon and nitrogen) in bone collagen from faunal and human remains is the most common used technique to study the new farming strategies as well as human diet. In addition, strontium isotopes, which are able to provide insights about the provenance of individuals, can help to correlate dietary shifts in specific individuals, and are also useful to explore the demographic structure of a community. The aim of this thesis is to study the impact of the Neolithic arrival to the Iberian Peninsula on autochthonous hunter-gatherers and their lifestyle and the evolution of the following Neolithic communities. Here, I applied the most advanced methods currently used in paleogenomic research, such as Next Generation Sequencing (NGS) and the capture of 1240K informative SNPs of the human genome. Thanks to these methods we have been able to recover genomewide data from eleven individuals ranging from ~ 13000 cal BP to 5000 cal BP. Moreover, we have produced more than 200 carbon (δ13C) and nitrogen (δ15N) isotopic collagen values, increasing considerably the dataset available for the Iberian Peninsula at this period, and even more so for the isotopic collagen data available on Early Neolithic fauna remains. In addition, we have generated the first big published data set of more than 80 strontium values (87Sr/86Sr) of human enamel and created a preliminary bioavailable strontium map of the Pre-Pyrenean landscape with more than 100 samples. The genetic results showed a unique genetic structure in Iberian HG, resulting from admixture of individuals related to Goyet Q-2 (Magdalenians) and Villabruna (Western Hunter-Gatherers) genetic clusters. This suggests a survival of two lineages of Late Pleistocene ancestry in Holocene western Europe, in particular the Iberian Peninsula, whereas HG ancestry in most other regions was largely replaced by Villabruna-like ancestry. Traces of the dual huntergatherer lineages (Goyet Q-2 and Villabruna) were also found in Iberian Early Neolithic individuals, arguing for admixture with local Iberian hunter-gatherers. Early Neolithic individuals with higher amounts of Goyet Q-2 like ancestry were located in Southern Iberia, possibly reflecting the previous hunter-gatherer structure in that territory. During Middle Neolithic times this signal start to be more homogenized but the Iberian sites continued having a higher Goyet-2-like ancestry. The results of the stable isotope analysis suggest a higher importance of animal husbandry than agriculture/crop farming/plant cultivation, although the domestic species studied did not show a special feeding signal compared to the wild ones. Besides, the large data set available now for humans from the Late Neolithic and the Chalcolithic period allows to test the presence of two different eco-geographic regions with statistics significance in isotopic values. The use of strontium isotopes with the radiocarbon dates has allowed us to distinguish different burial phases despite a common terrestrial diet.