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Early humans were choosy about their rocks, study finds

A research team, led by the Nagoya University Museum and Graduate School of Environmental Studies in Japan, has brought clarity to the distinctions in the physical attributes of rocks utilized by early humans during the Paleolithic era. Their findings challenge the notion that humans chose rocks solely based on ease of detachment, indicating a more nuanced understanding and technical skill in selecting the best rocks for tool creation.

Published in the Journal of Paleolithic Archaeology, the research sheds light on the stone tools employed by as they migrated from Africa to Eurasia. Rocks like obsidian and flint were crucial for cutting, slicing, and crafting ranged weapons, playing a significant role in early human culture.

Focusing on prehistoric sites in the Jebel Qalkha area, southern Jordan, archaeologists Eiki Suga and Seiji Kadowaki from Nagoya University delved into three chronological periods during the geographic expansion of Homo sapiens in Eurasia, starting from the Middle East. Their analysis centered on flint nodules from outcrops exploited during the Middle and Upper Paleolithic (70,000 to 30,000 years ago).

The researchers propose that Paleolithic humans possessed a deliberate understanding of which rocks were suitable for tool-making, intentionally seeking them out. Their hypothesis suggests that these early humans specifically looked for flint that was translucent and smooth, as it facilitated easy detachment from the rock face and shaping into sharp edges.

Investigation of mechanical properties of rocks suggested that paleolithic humans changed their choice of raw material to suit their morphologies and production techniques. Credit: Eiki Suga, Reiko Matsushita

To assess the mechanical properties of rocks, the research group utilized a Schmidt Hammer and a Rockwell Hardness Device. The Schmidt Hammer gauges the elastic behavior of a material, measuring its rebound hardness after being struck, while the Rockwell hardness device assesses rock strength by pressing a diamond indenter on the surface.

As expected, initial findings indicated that fine-grained flint required less force to fracture than its medium-grained counterpart, making it preferable for producing small stone tools. This aligns with the prevalence of fine-grained flint in stone tools from the Early Upper Paleolithic (40,000 to 30,000 years ago).

However, a previous study by the same team revealed a paradox: during the Late Middle Paleolithic and Initial Upper Paleolithic (70,000 to 40,000 years ago), medium-grained flint was more commonly used in stone tools. The team delved further and discovered that much of the fine-grained flint in the area contained internal fractures due to geological activities, rendering it unsuitable for large stone tools like Levallois products and robust blades.

This nuanced suggests that Paleolithic humans, far from choosing rocks solely based on ease of modification, considered multiple factors. Despite the difficulty in shaping medium-grained flint into tools, its durability made it a preferred choice for larger tools, offering a compelling glimpse into the thoughtful decision-making of our ancestors as they selected rocks for crafting stone tools.

The geographic expansion of Homo sapiens into Eurasia started in the Middle East.The research team focused on prehistoric sites and raw material sources (outcrops) in the Jebel Qalkha area, southern Jordan (photo). Credit: Professor Seiji Kadowaki

The discoveries have left Suga enthused, emphasizing the intricate nature of our ancestors' behavior. “This study highlights the adaptability of Paleolithic humans, showcasing their ability to adjust their choice of raw materials based on the morphology and production techniques of stone tools,” he remarked.

The research team posits that prehistoric humans possessed a sensory understanding of rock characteristics, intentionally selecting stone materials tailored to the desired form and production technique of stone tools. This deliberate selection of lithic raw materials emerges as a crucial aspect of stone tool production, indicative of a flexible technological behavior attuned to specific situations.

Suga also underlines the importance of studying cultural remains, such as stone tools, from archaeological sites to unravel the mysteries surrounding the expansion of Homo sapiens 50,000 to 40,000 years ago. While DNA analysis provides insights into interactions with Neandertals and Denisovans, it falls short in revealing the actual historical events and their unfolding.

To comprehend the factors that propelled Homo sapiens' success, Suga stresses the significance of delving into cultural artifacts, particularly stone tools. This resourceful approach serves as a vital record for unraveling the of human technological behavior, environmental adaptation, and the dynamics of population growth during that pivotal era in human history.

Source: Nagoya University

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