Key Points
- Using high-resolution spectroscopic techniques (µ-Raman and µ-FTIR), researchers identified microscopic residues of the non-edible plant Isatis tinctoria (woad) on Upper Palaeolithic stone tools, providing the first archaeological evidence of indigotin from this period.
- The presence of wear patterns and indigotin precursors suggests that early humans deliberately processed woad through grinding and fermentation, indicating a surprisingly sophisticated understanding of plant chemistry and its applications beyond food.
- This study redefines the cognitive and cultural capabilities of Upper Palaeolithic humans, showing they exploited plants for medicinal, cosmetic, or symbolic uses.
A recent study used high-resolution spectroscopic methods, such as micro-Raman (µ-Raman) and micro-Fourier-transform infrared spectroscopy (µ-FTIR), to learn more about Upper Palaeolithic humans. This study, which was published in the journal PloS One, used µ-Raman and µ-FTIR spectroscopy to discover how Upper Palaeolithic humans deliberately processed a non-edible plant (Isatis tinctoria L.) known as woad to use for various functions. This study was led by researchers from Italy’s Ca’ Foscari University of Venice and the University of Padua (1).
What is woad?
Woad is a medicinal plant with an extensive history of being used as an indigo dye (2). The plant has been shown to possess several biologically active compounds, including several alkaloids (2). In modern times, studies have shown that woad has anti-inflammatory, anti-tumor, antiviral, and antimicrobial properties (2).
What was the experimental procedure?
As part of the experimental procedure, the research team used a multi-analytical strategy that combines morphological observation with high-resolution spectroscopic methods—specifically µ-Raman and µ-FTIR. Using these methods, the researchers identified microscopic residues of Isatis tinctoria on the surfaces of unmodified pebbles (1). These residues, entrapped in the crevices and topography of the stones, were accompanied by wear patterns indicating deliberate grinding or pounding actions (1).
As a natural source of indigotin, Isatis tinctoria possesses several chemical properties that early humans would find valuable. The researchers proposed that early humans mechanically broke down the leaves, thereby releasing indoxyl glycosides, which, through fermentation, led to the formation of indigotin, which is a process that reflects an advanced understanding of plant properties (1).
According to the study, this is the first time indigotin, a secondary metabolite, has been detected in archaeological micro-residues from this period (1).
What are the implications of this study?
The implications of this study are that it introduces new possibilities for the presence of indigotin in a Palaeolithic context. The study suggests that early humans were not only gathering plants for food or utility, but they were also capable of exploring and exploiting the nuanced properties of their environment (1). The study’s findings make it clear that non-edible plants were also important to Upper Palaeolithic communities, indicating a richer and more complex behavioral repertoire than previously assumed.
This study unique is that it uses a multiscale approach that prioritizes physical evidence over assumption (1). Although organic remains are inherently fragile and less likely to survive the passage of millennia compared to stone tools or bones, the research team demonstrates how analytical methods can retrieve important traces that have long gone unnoticed (1).
In this case, the researchers studied simple pebbles, which bore microscopic use-wear and embedded plant residues. The combination of microscopic epidermal plant fragments with chemical signatures linked to indigotin precursors gives strong support to the conclusion that these stones were used purposefully in the processing of Isatis tinctoria (1).
What should future studies concentrate on?
As the first study to offer reproducible evidence of non-food plant processing in the Upper Palaeolithic, this work establishes a new framework for understanding the cognitive and cultural landscapes of early modern humans (1). It speaks to the origins of pharmacognosy, the early use of natural dyes, and the possibility that Homo sapiens had a proto-scientific understanding of their world long before the dawn of agriculture (1).
By enriching our perception of plant-human relationships in early history, this study opens the door for future investigations into how ancient communities may have manipulated botanical resources for purposes that go well beyond the dinner table (1).
References
- Longo, L.; Veronese, M.; Cagnato, C.; et al. Direct Evidence for Processing Isatis tinctoria L., a Non-nutritional Plant, 32–34,000 Years Ago. PLoS One 2025, ASAP. DOI: 10.1371/journal.pone.0321262
- Speranza, J.; Miceli, N.; Taviano, M. F.; et al. Isatis tinctoria L. (Woad): A Review of Its Botany, Ethnobotanical Uses, Phytochemistry, Biological Activities, and Biotechnological Studies. Plants (Basel). 2020, 9 (3), 298. DOI: 10.3390/plants9030298
