Abstract
More than 2 million years ago in East Africa, the earliest hominin stone tools evolved amidst changes in resource base, with pounding technology playing a key role in this adaptive process. Olduvai Gorge (now Oldupai) is a famed locality that remains paramount for the study of human evolution, also yielding some of the oldest battering tools in the world. However, direct evidence of the resources processed with these technologies is lacking entirely. One way to obtain this evidence is through the analysis of surviving residues. Yet, linking residues with past processing activities is not simple. In the case of plant exploitation, this link can only be established by assessing site-based reference collections inclusive of both anthropogenic and natural residues as a necessary first step and comparative starting point. In this paper, we assess microbotanical remains from rock clasts sourced at the same quarry utilized by Oldowan hominins at Oldupai Gorge. We mapped this signal and analysed it quantitatively to classify its spatial distribution objectively, extracting proxies for taxonomic identification and further comparison with freestanding soils. In addition, we used blanks to manufacture pounding tools for blind, controlled replication of plant processing. We discovered that stone blanks are in fact environmental reservoirs in which plant remains are trapped by lithobionts, preserved as hardened accretions. Tool use, on the other hand, creates residue clusters; however, their spatial distribution can be discriminated from purely natural assemblages by the georeferencing of residues and statistical analysis of resulting patterns. To conclude, we provide a protocol for best practice and a workflow that has the advantage of overcoming environmental noise, reducing the risk of false positive, delivering a firm understanding of residues as polygenic mixtures, a reliable use of controls, and most importantly, a stronger link between microbotanical remains and stone tool use.
Highlights
More than 2 million years ago in East Africa, the earliest hominin stone tools evolved amidst changes in resource base, with pounding technology playing a key role in this adaptive process
Paleoanthropologists have studied the origins of tool use among human and non-human primates for decades, with pounding technology playing a central role in this quest for its shared legacy of technical gestures with monkeys and apes[1,2,3,4,5]
Direct evidence of plant processing by early Pleistocene hominins is absent, with stone tools at the center of this pursuit, for they allow the extractive behavior at the interface between technology, diet, and the environment
Summary
More than 2 million years ago in East Africa, the earliest hominin stone tools evolved amidst changes in resource base, with pounding technology playing a key role in this adaptive process. Microbotanical remains from archaeological artifacts are prone to excavation and laboratory c ontamination[33,34,35], a serious concern for tool functional interpretation in ancient phytolith and starch s tudies[36,37,38,39,40,41] that routinely model natural controls to argue for or against the authenticity of putative residues, a practice going back four decades[42] We fill this gap with the first baseline for the study of plant residues at the most influential and oldest locality for the understanding of prehistoric percussion tools[19,43,44]: Olduvai Gorge ( Oldupai)(Fig. 1), with implications for other sites as well. Composition and location of phytogenic palimpsests help discriminate natural from anthropogenic agency in residue accumulation, as well as environmental false positives, setting the minimum requirement for future work on plant residues from Oldowan pounding tools
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