RESKUE · Residues: Unlocking the key to ancient plant use. Identification, extraction and study of organic resiuddes adhering to stone tools as a means to recover empirical evidence of prehistoric plant use

Final Activity Report Summary - RESKUE (Residues: Unlocking the key to ancient plant use. Identification, extraction and study ... to recover empirical evidence of prehistoric plant use)

The aim of the RESKUE project was to unlock the key to ancient plant use in Europe through the extraction and identification of ancient starch granules adhering to archaeological artefacts. Starch is the most direct dietary source of glucose, which is the essential provider of metabolic energy. Almost 20 to 25 % of an individual's resting energy is required to maintain the brain, which has roughly 16 times the energy demand of muscle tissue. Starch-based foods constitute around 50 to 70 % of most humans' energy intake today. Nevertheless, evidence for starchy foods such as tubers, roots and seeds can be difficult to find on some archaeological sites. Starch is a biodegradable molecule. When we eat, the amylase in saliva begins the degradation process within the mouth. Starch granules were used for some time in archaeology to identify aspects of diet and plant trajectories. Since the mechanisms by which starch survives into archaeological time were unclear, biochemical proof was needed to demonstrate the integrity of this ancient material. Traditional methods of identification included assessments of the morphology of the granules through the use of stains and via the birefringent Maltese cross pattern which was clearly visible using a light microscope. Birefringence though is a characteristic commonly found in materials with crystalline layers arranged in a concentric pattern and none of the abovementioned methods are conclusive tests of starch. The only unequivocal test for starch is to degrade it using an alpha amylase, a specific enzyme for the chemical linkages contained in starch which uniquely degrades starch. Over the duration of this project, ancient starch of a range of ages, from many different contexts, was degraded with alpha amylase. This proved beyond all doubt and for the first time that biochemically intact starch granules could survive into archaeological time. Dental calculus is a premium source of ancient starch which is directly related to diet. Because of the location of starch within the calculus the risk of contamination is minimal. Dental calculus occurs when plaque biofilms accumulate and mineralise. It is associated with chronically poor oral hygiene and is common on archaeological skeletons of all periods. It actually even survives on some Pliocene hominids. When samples of dental calculus are gently degraded, the calcium dissolves and the plant macrofossils which are trapped inside are released. These can then be concentrated and mounted on microscope slides for observation and enzymes' application. Samples of dental calculus from a range of locations were studied. They included human and animal archaeological samples from Anatolia, human samples from a range of sites in the United Kingdom and modern chimpanzee material from Uganda. The idea of extracting plant macrofossils from dental calculus had been raised before this project but its potential was not realised and an appropriate method for macrofossils' extraction was not developed. Using this new method it would be possible to explore the consumption of carbohydrates from specific plants in pre-agricultural diet, something that had up to now been virtually impossible, apart from very rare circumstances. Much theoretical work existed on the role of carbohydrates in pre-agricultural diet and now, for the first time, the application of this method would render possible to test the theories against empirical data. This work was anticipated to have a direct impact on the study of the origins of agriculture, the transition of humans from hunter-gatherers to farmers and the role of carbohydrates in human evolution. Nevertheless, dental calculus was a limited resource, the potential of which was appreciated not up to now. Its study was destructive and its use should be carefully monitored. In case, however, this new method was applied with due rigour, it should allow us to explore directly the question of carbohydrate consumption during our evolution and later pre-agricultural life, something that was up to now speculated upon but impossible to study. Starch extraction was also undertaken on archaeological soils and artefacts in the United Kingdom and Turkey. Even though this work was still ongoing by the time of the project completion, a picture of survival potential for starch had started being constructed.

Data: CORDIS, © European Union