Chewing tar in the early Holocene: an archaeological and ethnographic evaluation.

Aveling, E.M. ; Heron, C.

Introduction

Amorphous lumps of putative tar with human tooth impressions have been recovered from several prehistoric sites in Scandinavia (e.g. Bang-Andersen 1976; Larsson 1982; Johansson 1990; Regnell et al. 1995; Hernek & Nordqvist 1995), southern Germany (Rottlander 1981, Schlichtherle and Wahlster 1986, Alexandersen 1989) and Switzerland (Schoch 1995). The term 'tar' is used here to refer to a product of the destructive heating of wood, bark or resin. Although small in number, these finds date to the Mesolithic and Neolithic periods and can be described as hardened lumps or shapeless masses, brown to black in colour, with distinctive tooth impressions. Similar, although apparently unchewed lumps of tar have also been recovered (e.g. Clark 1954: 167; Larsson 1983: 75; Binder et al. 1980; Cattani 1993). Although mentioned briefly in site reports, the scarcity of such finds combined with the difficulty in identifying amorphous samples of organic matter has limited evaluation of their origin and use. More recently, efforts to characterize organic resinous substances, considered to have been used to fulfil a wide range of non-dietary functions, including use as adhesives and sealants in prehistoric Europe, has stimulated greater interest in these finds and this note addresses some of the Scandinavian examples (see also Aveling 1997). This work forms part of a larger project into the use of molecular marker compounds to identify organic natural products from Mesolithic sites in northern Europe (e.g. Aveling & Heron 1998).

Background

Recent chemical investigations of adhesives, sealants, waterproofing agents and other amorphous organic substances from prehistoric contexts in Europe has confirmed the widespread use of birch (Betula) bark tar (Pollard & Heron 1996). Birch-bark tar is a black-brown product obtained by the destructive heating of birch bark in a vessel or oven with a limited supply of air. Molecular information, obtained principally by gas chromatography/mass spectrometry, has been highly successful in identifying a number of archaeological samples from the Neolithic onwards (e.g. Sandermann 1965; Hayek et al. 1990; 1991; Reunanen et al. 1993; Heron et al. 1991; Binder et al. 1990; Charters et al. 1993; Regert 1996; Regert et al. 1998). Identification is based on the recognition of a suite of triterpenoid molecules mostly based on the lupane carbon skeleton, including betulin, lupeol and lupenone. These molecules are consistent with those present in authentic fresh birch bark, taking into consideration modifications to the carbon skeleton due to thermal effects as the bark is heated and alteration during long-term burial. As the references above testify, the recognition of birch-bark tar in the toolkit of Neolithic Europe is becoming a common occurrence. For example, it features among the frozen remains of the Neolithic body recovered from a glacier in the Otztal Alps on the Austrian-Italian border. The copper axe, arrowheads and arrow flights were hailed using birch-bark tar as the adhesive medium (Sauter et al. 1992; Spindler [TABULAR DATA FOR TABLE 1 OMITTED] 1994: 89,124-5). Regert (1996) has conducted a systematic study of tar samples from two Neolithic sites (Chalain, Jura and Giribaldi, Nice) in France. Birch-bark tar was characterized in nearly all cases, although mixtures of birch tar with other plant products were also identified. One of the samples from Chalain was not consistent with a birch origin and is considered to represent the exploitation of non-local fossil bitumen seepages (Regert et al. 1998). Other alternatives to the use of birch-bark tar in Neolithic and later contexts in northern Europe include a bituminous substance on an Early Bronze Age knife from Xanten-Wardt, Germany (Koller & Baumer 1993), a Pinaceae tar, possibly from Pinus spp. (Heron et al. 1991), and beeswax (Heron et al. 1994) on Neolithic pottery fragments from Ergolding Fischergasse, Germany. These substances are easily distinguished from birch-bark tar on the basis of characteristic molecular marker compounds (Pollard & Heron 1996). More recently, Sheldrick et al. (1997: 365) have reported the survival of a conifer-based softwood pitch, probably Pinus spp., as a hafting glue on a Palaeolithic barbed antler point from Gransmoor, Yorkshire, although how this interpretation was arrived at is not made explicit. Further afield, Evershed and coworkers (Evershed et al. 1997a) have reported the presence of beeswax in conical cups and lamps of Late Minoan date from Mochlos, Crete. Until recently, molecular analysis of Mesolithic samples had not been undertaken. To date, the only previous analyses of 'chewing-gums' have been reported by Rottlander (1981) and Schoch (1995). Nine lumps, all with discernible tooth impressions, from the Neolithic wet site of Hornstaad-Hornle 1 in southern Germany were analysed by thin-layer chromatography and determined to be birch-bark tar (Rottlander 1981). Using the same method, Schoch (1995) suggested a birch-bark tar origin for two more lumps with tooth impressions from the Neolithic site at Seefeld, Switzerland.

The Mesolithic samples

The samples shown in TABLE 1 originate from five Scandinavian Mesolithic sites spanning the Maglemose (c. 9500-7600 BP), the Kongemose (c. 7600-6500 BP) and the Ertebolle (c. 6500-5200 BP) cultures. FIGURE 1 shows the example from Bokeberg, Sweden. Pollen analysis of a sub-sample of this chew suggested that the tar was derived from Pinus with 56% of the 400 grains present attributed to Pinus, 18% to Corylus and 9% to Quercus pollen (Regnell et al. 1995). Tiny flecks, weighing between I and 2 milligrams, were removed from the samples, solvent extracted and analysed in Bradford by gas chromatography/mass spectrometry (GC/MS). All are consistent with a birch-bark tar origin through recognition of a number of characteristic compounds and comparison with authentic tar samples (e.g. Aveling 1998; Aveling & Heron 1998). By way of example, FIGURE 2 compares an authentic birch (B. pendula) bark tar, prepared by heating fresh bark for 10 minutes in a sealed container at 350 [degrees] C, with the chloroform/methanol soluble portion of the sample from Segebro, Sweden. This distinctive pattern of triterpenoid molecules has not been seen in any other authentic wood or bark products analysed. The absence of diterpenoid molecules in these samples rules out the presence of resinous substances of the Pinaceae family, such as pine, spruce or fir. Similarly, a contribution from beeswax is eliminated as no n-alkanes nor wax esters were detected. Although triterpenoids are present in solvent extracts of fresh bark from other trees, including hazel, rowan and poplar, these give markedly different qualitative and quantitative patterns to those of birch-bark tar. The apparent contradiction between the molecular and pollen data for the Bokeberg sample is resolved if Betula pollen is largely absent from stripped bark or if it is destroyed by heating during tar production. The pollen identified by Regnell et al. (1995) is plausibly a measure of the background 'pollen rain' adhering to the tar surface (Julie Bond pers. comm.).

Chewing birch-bark tar in the Mesolithic

Although the primary function of teeth is to bite, chew, crunch and grind food, chewing plant or animal products serves a number of alternative roles, such as cleaning teeth and gums, freshening breath, quenching thirst, alleviating dental ailments and sore throats, and as a means of delivering medicinal and psychoactive agents into the body. There is a large body of ethnographic and historical literature from around the globe describing the use and roles of specific masticants (e.g. Wolff 1927: 1074-7; Howes 1949: 139; Murphey 1958; Eibl-Eibesfeldt 1975; Edlin 1978: 81; Lee 1990: 163; Rooney 1993; Atawodi et al. 1995; Johns et al. 1996). However, the applicability of these accounts in helping to explain the Mesolithic chews is open to debate. A plausible functional explanation for the tooth-marks in the Scandinavian examples is that chewing softened the tar prior to use as an adhesive or sealant. Freshly produced tar hardens on cooling but must be rendered pliable if it is to be used in hafting composite tools and so on. However, experiments have suggested that a coating of saliva actually reduces the capacity of the tar to adhere (Jurgen Weiner pers. comm.). Alexandersen (1989) also proposes a functional explanation, considering that amorphous aggregates formed a stock of tar to be reheated from time to time to facilitate the removal of smaller pieces for use. Once sufficiently softened, it would then be easy to bite a piece off.

Although the major constituents of birch-bark tar have been identified in a number of publications, the presence of stimulants or addictive agents in low abundance has not been established. However, it is unlikely that parallels can be drawn with the ubiquitous practices of chewing betel (Areca catechu L.) nut, tobacco (Nicotiana spp.) or coca (Erythoxylum spp.) leaves in other parts of the world. Treatment of certain medical or dental conditions is possible. Birch bark has a natural resistance to fungal attack (O'Connell et al. 1988) and there is abundant ethnographic evidence that organic substances can be preserved in birch-bark containers. Historical evidence records the use of birch-bark tar in the treatment of sore throats (Rajewski 1970) as well as sore skin, blistered lips, frost bite and ringworm (Hoeg 1976); these observations hint at antiseptic properties common to many resinous substances. Chewing also stimulates saliva production and so could help to keep teeth and gums clean. In northern Sweden, chewing fir resin has been used as a means of preventing dental ailments and this practice continued into the 20th century (Johansson 1990). Resins of the Pinaceae family exude naturally from the trunk and can easily be removed and chewed without any further preparation. Tapping increases the flow without serious damage to the tree. Ethnographic studies of Native Americans and Inuit in the boreal forests of North America document the collection and chewing of resin from several coniferous species, of which spruce (Picea spp.) is considered to be the most important (Kuhnlein & Turner 1991: 59). In ethnographic studies conducted by Vilkuna (1964) in the Lapp area of northern Sweden, reference is made to observations in 1731 by Linne, who described collection of resin from spruce trees which was then chewed. The same custom was found amongst the Finnish Lapps. Vilkuna also records observations by Jacob Fellman, who wrote in 1826 that the Lapps chewed Scots pine (Pinus sylvestris) resin in the absence of tobacco. Chewing is described as a treatment for toothache and it may also have acted as a decongestant; literally 'it pulled overflowing water from the lungs' (1964: 298). Vilkuna also notes an 1817 account written by Goltlund of a church service in Finland at which half of the congregation (all women) were chewing resin to keep themselves awake. Goltlund noted that people chewed to pass the time, to keep teeth white, to prevent the invasion of scurvy into the gums and to relieve stomach pains and heartburn. The most enthusiastic chewers were adolescents and old women. The preparation of chews required practice and so older women often 'prechewed' the resin for children. Although the majority of Vilkuna's ethnographic cases relate to chewing tree resins, reference is also made to the chewing of birch-bark tar for similar purposes in 19th-century Siberia. The tar had to be prepared in a specific manner and only women could be present.

Studies of the tooth impressions in the Mesolithic chews highlight that, in four of the five cases, the tar was chewed by children and adolescents (see references in TABLE 1). The age range seems to be approximately 6 to 15 (Nordqvist 1994), corresponding to the time when the deciduous milk teeth are lost. The number of samples is too few at present to deduce a widespread pattern but analysis of new finds can be compared with these initial observations. As a footnote, it has been speculated that polished sections on the incisors and canines of the frozen remains of the Neolithic body from the Austrian-Italian Alps may have occurred as a result of chewing birch bark tar (Spindler 1994: 183).

Conclusions

The transformation of birch bark into an extensively used tarry product was already well established in Mesolithic Europe and may have its origins in the Upper Palaeolithic or earlier populations of Europe. Its presence is now documented throughout the Mesolithic, and preparation and use continued into the Neolithic and subsequent periods. Historical accounts in central and eastern Europe provide evidence of many other uses and serve to highlight the extent to which birch-bark tar and wood pitch were once represented in daily life (Rajewski 1970; Piotrowski 1997). Many suggestions can be mustered to explain the chewing of birch-bark tar in Mesolithic and Neolithic Europe. Recent ethnographic accounts from Scandinavia largely highlight the chewing of Pinaceae resins and these suggest a role primarily in cleaning teeth and gums, although other remedying effects are hinted at. It is curious that in the Mesolithic, a 'synthetic' tar appears to have been favoured over, for example, pine resin which can be procured easily. The production of birch-bark tar requires much more time and effort. Differential survival of these substances is unlikely. This may suggest that, once prepared, birch-bark tar was better suited to the tasks of halting composite tools, waterproofing and other less visible uses.

Recent analytical investigations of amorphous plant and animal products have demonstrated archaeological potential over a considerable chronological and geographical range (e.g. Boeda et al. 1996; Pollard & Heron 1996; Evershed et al. 1997b). In contrast to the site-specific investigations of single samples, the analysis of finds from a number of sites offers considerable opportunities for archaeological evaluation. The secure identification of specific products from molecular patterns can assist in assessing the roles these substances played and in determining the use of artefacts, on which these residues survive.

Acknowledgements. We are indebted to the following for allowing us an opportunity to take samples for analysis and for their overall assistance and guidance throughout: Lars Larsson of the University of Lund, Sweden; Axel Degn Johansson, South Zealand Museum, Yordingborg, Denmark; Peter Vang-Petersen, National Museum, Copenhagen; Sveinung Bang-Andersen of the Archaeological Museum, Stavanger, Norway and Per Karsten and Bengt Nordqvist of the Central Board of National Antiquities, Sweden. We also wish to thank Martine Regert for making a copy of her Ph.D thesis available, Julie Bond, Timothy Johns (McGill University) and Gill Thompson for their comments on an earlier draft of this paper, and Jurgen Weiner for illuminating discussions. The support of the British Academy is also acknowledged with gratitude for the award of a studentship to one of us (EA).

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