Direct evidence for processing Isatis tinctoria L., a non-nutritional plant, 32-34,000 years ago

Area of Science:

• Archaeology
• Paleobotany
• Materials Science

Background:

• Plant remains are rarely preserved in Palaeolithic sites, leading to an incomplete understanding of their use.
• Current archaeological paradigms often overlook the significance of plants in early human diets and practices.
• Plants were crucial for survival and technological development in the Upper Palaeolithic.

Purpose of the Study:

• To provide robust evidence for the deliberate processing of plants in the Palaeolithic era.
• To investigate the use of Isatis tinctoria L. leaves by humans 34,000–32,000 years ago.
• To offer a new perspective on Upper Palaeolithic human behavior and technical knowledge.

Main Methods:

• Morphological analysis of pebble surfaces.
• Spectroscopic analysis, including micro-Raman (µ-Raman) and micro-Fourier-transform infrared (µ-FTIR) spectroscopy.
• Stringent contamination control and biomolecular analysis of plant fragments.

Main Results:

• Physical and biomolecular evidence for the pounding and grinding of Isatis tinctoria L. leaves.
• Discovery of leaf epidermis fragments on unmodified pebbles with associated use-wear traces.
• Identification of indigotin precursors, suggesting potential use as a blue dye (woad) or for medicinal purposes.

Conclusions:

• The study provides strong evidence for the intentional use of non-edible plants in the Upper Palaeolithic.
• Isatis tinctoria L. processing indicates advanced technical and ecological knowledge among early humans.
• The exact application (dye, medicine, or both) remains undetermined, opening new avenues for research into plant utilization.