<論説>石器認定の思考 --日本列島における約四万年前を遡る石器の認識-- (特集 : 嘘)

Abstract

現生人類の渡来(約四万年前)以前に、日本列島に人類が到達していたか否か。この古くて新しい議論の核心には、石器認定(石器と自然礫の区別)の難しさがある。この難題に方法論的な展望を見いだすため、旧石器考古学に関わる捏造事件を石器認定に注目して回顧する。捏造者は何を意図して、なぜ当時の研究者らが誤ったのかをたどる。すると、新たな資料の発見に先立って、既存の学説や時代観、編年観に沿って、今後発見されるべき資料の輪郭が予測されていて、その予測に当てはまる捏造資料を受け入れたことが確認される。型式論・系統論的判断とは異なる石器認定法としては、原材料の異地性を明らかにする方法、割れ面観察の徹底によって人為性を読み取る方法等、石器研究の体系に沿った方策が考えられるが、既往の理解に当てはまらない資料が受け入れられるのは容易ではない。現在の研究状況はこの傾向をいっそう加速させると予想される。

Whether humans had already reached the Japanese archipelago before the arrival of modern humans approximately 40, 000 years ago has long been debated in Japanese prehistoric archaeology. The following discussion will provide empirical data to clarify the timeline and process by which modern humans, who dispersed across East Asia, achieved an “out of Eurasia” expansion. Additionally, it will shed light on how these populations adapted to environments distinct from those of the Eurasian interior. The difficulty in answering this question lies in the challenge of distinguishing between lithic artifacts and geofacts naturally flaked stones that resemble man-made artifacts. As with archaeological cases around the world, researchers in Japan have been troubled by questions such as how to discern traces of human activity from the materials in question, how to reach a common understanding among researchers who study lithic artifacts of different materials, and whether it is even possible to empirically distinguish lithic artifacts from geofacts on an individual basis. In this study, the author revisits incidents of forgery within Paleolithic archaeology -- such as the Piltdown Man, the Kanagi geofact incident in the 1950s, and the Fujimura scandal -- to find a methodological perspective to address this difficult problem by focusing on the distinction between artifacts and geofacts. For each case, the author examined what the forger intended through the act of fabrication and why knowledgable researchers of the time were misled. As a result, the study revealed a vulnerability in archaeological thought --what might be called “thinking traps.” In other words, even before the discovery of new materials, the prospective outlines of artifacts expected to be found in the future had already been anticipated in accordance with existing theories, views of the period, and chronological frameworks. The researchers at the time accepted forged materials that fit these expectations as authentic. This highlights the vulnerability of the typological-systematic approach that archaeology relies on, particularly in Paleolithic archaeology. In studies investigating the dawn of human habitation in certain regions, this vulnerability can lead to serious errors. To avoid such errors, methods consistent with the framework of lithic studies can be considered. These include methods such as revealing the exotic origin of lithic raw materials through chemical composition analysis and meticulously observing fracture surfaces to identify signs of intentionality. In this study, the author applied these methods to materials from the Sozudai and Kanedori sites. Stratigraphic analysis and observations of sediments adhering to the materials confirmed that the problematic artifacts from both sites were obtained from layers older than 40, 000 years ago. At the Sozudai Site, X-ray fluorescence (XRF) analysis revealed that the glassy rhyolite used as the raw material for the artifacts could only be sourced from a location 44 kilometers away from the site. At the Kanedori Site, the materials in question were composed of heterogeneous materials containing numerous phenocrysts, making it difficult to distinguish between the cortex and the fractured surface or to identify the direction of fractures under conventional lithic observation methods. To address this, the author applied the Phenocrysts Microscopic Observation Method, which the author developed. This method involves observing phenocrysts under a microscope to analyze the degree of weathering and detachment marks, contributing to a comprehensive understanding of the material. The results confirmed that the material could be evaluated as a unifacially retouched pointed tool. Furthermore, the author attempted to observe fracture wings on the phenocrysts and analyze differences in fracture speed at various parts of the artifact -- likely reflecting variations in force applied during tool production. Through these analyses, the possibility that these are manmade artifacts predating 40, 000 years ago has increased significantly. However, even if such approaches are adopted, it is not easy for archaeologists to accept artifacts that surpass the boundaries of current knowledge. The academic environment and research conditions surrounding archaeologists today are expected to further accelerate this tendency.