Applications of biomolecules and isotopes to infer ancient human subsistence activities : Olduvai Gorge, northern Tanzania (early Pleistocene) and Valdocarros, Spain (mid-Pleistocene)

Abstract

An ongoing debate in human evolution research is whether there are connections between eco(hydro)logic changes, and the essential resources (food, water, shade) used by early humans (hominins) that lived in a highly competitive and biodiverse environment. Water and its accessibility provide a direct link between climate, landscape, and large-mammal behaviors, and therefore exerted direct influence as well on early human activities. Additionally, in human evolution, the use of fire is considered a technological landmark; in particular its implications as widening diets and calories intake, defensive tool, and heat source. However, the early development of pyro-technology remains controversial because its remains are easily reworked and their identification in the archaeological record can be impeded. Biomarkers are chemical ‘fossils’ that function as a foundation of high-resolution sedimentary (paleo)climate and (paleo)environmental reconstructions, as well as preservation of plant tissues. Such ‘fossils’ include a wide range of diagnostic organic compounds with known origins, which – due to their relative stability during geologic and biochemistry processes – offer uniquely quantitative insights into ancient landscape conditions across space and through time. Furthermore, stable (lipid) biomarkers derived from vegetation, such as leaf-waxes (i.e., n-alkyl lipids) are commonly preserved in soils and lake sediments associated with hominin archaeological localities. Since plant biomarkers comprise repeated hydrocarbon (–CH2–) sub-units, which differ in atomic composition (13C/12C [δ 13C]; 2H/1H [δD]) among plant types, it is possible to reconstruct the composition of vegetation communities using plant biomarker-specific isotopic signatures. As such, the combination of sedimentary plant biomarker δ 13C measurements offers remarkable insights into vegetation and hydroclimate conditions during geologic history. The environmental factors that drove differences in apparent behavioral development (i.e., evolution) between hominin species during the last 2 million years remain a matter of heated debate. This research focuses on novel biomarker-specific isotope data acquisition to (1) resolve the importance of different dietary options and water resources among past hominin species, and (2) improve upon our current knowledge of how ancient humans adapted to dramatic climate change regarding their (pyro-)technological advancements.