Omnivory and human evolutiona new perspective on paleodiets using the faecal biomarker approach

Resumen

Paleodietary research is becoming an increasingly important and socially relevant topic thanks to a renovated focus of evolutionary medicine on a ¿healthy primitive nutrition¿. Most authors agree that meat eating was one of the main factors to have triggered the emergence of physiological and behavioural traits defined as the ¿human package¿. Yet, we know little about Paleolithic diets. Most of our information comes from isotope analysis, which reflects only the protein sources. Supporting information comes from the recurrent occurrence of butchered bones in archaeological sites, which together with isotope analysis have awarded a leading role to meat eating in our evolution and diet. Meanwhile, plant intake is only known from scattered evidence of plant remains, phytoliths analysis and dental calculus. The polarity of the record has conveyed an image of Paleolithic diets as largely based on large game hunting. Nevertheless, to date we are not substantially closer to an understanding of our ancestors' regular meals and how we became capable of sustaining such a largely carnivorous diet. The main goal of this dissertation is to propose a new method capable of providing visibility to plant and animal tissue intake in Paleolithic diets. We believe that faecal biomarkers, because they are uniquely formed in the intestinal tract of most mammals and given their relationship with dietary habits, are useful to approach the relative proportions of animal and plant tissues in our ancestors¿ diets. In order to reach this aim, our objectives are: I) to verify faecal biomarker preservation in Pleistocene archaeosedimentary contexts; II) to implement the faecal biomarker approach in soil samples containing faecal matter and shed some light on the composition of the Neanderthal diet; and III) to provide a referential framework of non-human primate faecal samples that helps us to understand the adaptations that early human meat-eaters might have undergone in their way to becoming persistent meat eaters. We carried three case studies: two Paleolithic archaeological sites, Paisley Cave (Oregon) and El Salt (Spain), and modern wild chimapanzee and Gorilla from KIbale National Park and Bwindi Imprenetrable National Park. Our GC-MS analysis of 5ß-stanols of Paisley Cave coprolites and of the Middle Paleolithic site of El Salt showed that faecal biomarkers are a valuable analytical tool in the sourcing of faecal matter. Moreover, preservation is assessed through the oldest record of sterols and stanols in a Pleistocene archaeological setting. With the application of the faecal biomarker approach to the Middle Paleolithic site of El Salt we have corroborated the reliability of the approach, which has provided the first evidence of omnivory among hominins and challenged the previous picture of Neanderthals as top predators. Finally, we have also accomplished our third objective through the analysis of faecal biomarkers in wild chimpanzee and gorilla samples, which yielded important clues to meat ingestion-related problems that the earliest persistent carnivores possibly had to overcome. This work is a stepping-stone to a new field of research, since for the first time we are able to exploit the organic content of Pleistocene archaeosedimentary deposits, which will open a new window to the secrets entrapped in Paleolithic soils.