Plant Cuttings

Artistic reconstruction of ‘Lola’, whose DNA was found in the birch tar analysed by Theis Jensen et al. (2019). Photograph: Tom Bjorklund/PA. Image sourced from Ian Sample’s news article.

Mr Cuttings has had a letter, from an associate of a Mrs Trellis of North Wales, suggesting that the blog’s posts are a little on the long side. Always keen to see if he can do things better, Mr Cuttings has split this week’s post in two, to make two shorter items. Part 1 is what you’re reading here. Part 2 will be the next post. Do let Mr Cuttings know if this has been an improvement – or the alternative.

Following on from this blog’s previous post, about – amongst other things(!) – the forensic botanical value of dental calculus in deducing diets of Neolithic people, we begin this post with matters of an oral dimension. Our focus is again on something that’s intimately associated with teeth, chewing-gum*. Not the stuff that people chew on nowadays**, but a gum – that is actually a piece of pitch (“a tarry tree resin” (Olivia Young) – produced from the birch tree (Rory Boothe) from thousands of years ago [yes, it’s another tale from the Stone-Age]. First, some scene-setting.

It is widely-reported that chewing – sugar-free – gum is good for one’s oral health (e.g. here, here, here, here (Helen West; Kiet Ly et al., J Am Dent Assoc 139: 553-563, 2008; http://jada.ada.org/cgi/content/full/139/5/553; Michael Dodds, Journal of the Irish Dental Association 58(5): 253-61, 2012; PMID: 23573702; Melanie Nasseripour et al. (2022) Front. Oral. Health 3: 845921; doi: 10.3389/froh.2022.845921)***.

It is probably less well-known that chewing-gum* can be used to gain information about the oral health of prehistoric people. Yet, that is how ancient ‘chewing-gum’ has been exploited by Emrah Kırdök et al. (Sci Rep 13, 22125 (2023); https://doi.org/10.1038/s41598-023-48762-6) in their “Metagenomic analysis of Mesolithic chewed pitch … among stone age individuals.”. Analysing the DNA from samples of chewed [some with teeth-marks present] birch pitch from a site in Sweden that were dated to 9,890–9,540 years before present, they identified the presence of bacteria implicated in tooth decay (dental caries), and which may cause abscesses (Tim Newman). As Kırdök et al. caution, those sorts of microbes are expected even I the mouth of a healthy individual, and their presence alone is not evidence that hose ancient individuals suffered from those conditions. However, in one instance, there was an abundance of bacteria associated with periodontitis, gum disease. Using sophisticated analytical techniques, they concluded that the individual who had chewed that piece of resin “had probably suffered from periodontitis – with more than a 75% probability” (Anders Götherström & Emrah Kırdök). Overall, Kırdök et al. conclude that “Our results indicate a case of poor oral health during the Scandinavian Mesolithic”****.

Whilst you may also be tempted to conclude from this study that chewing gum* doesn’t help to improve one’s oral hygiene, a note of caution needs to be added. Although there are suggestions that birch pitch was used as a natural antiseptic for preventing and treating dental ailments and other medical conditions (Theis Jensen et al. (Nat Commun 10, 5520 (2019); https://doi.org/10.1038/s41467-019-13549-9), it seems more likely that the material was chewed to make it more pliable before using it as an adhesive in tool-making, e.g. to attach a stone axe to a wooden handle (Anders Götherström & Emrah Kırdök). It appears unlikely that the Stone-Age pitch-masticators were using birch pitch in the way a modern human should use dental chewing-gum. So, you’re probably best advised to continue with your dental hygiene routine that may use chewing-gum.

Which is interesting, but the real plants-and-people dimension comes from the analysis of the DNA of the plant material in the gum. Although caution is always needed when interpreting data from ancient DNA, Kırdök et al. are pretty confident that they have identified hazel (Corylus avellana) amongst the pitch samples, which might indicate that the seeds of this tree were consumed as part of the individual’s diet (e.g. Philippe Crombé et al., Quaternary Science Reviews 317, 1 October 2023, 108295; https://doi.org/10.1016/j.quascirev.2023.108295).

However, their DNA analysis also hints at presence of a wide range of other plants: European crab apple (Malus sylvestris); mistletoe (Viscum album) [per Kırdök et al., “Reports suggest that the plant could be used to produce poison for arrowheads, in addition to being utilised for medicinal purposes”]*****; apple (Malus domestica); wheat (Triticum aestivum) [indicating that bread was consumed by the people at this site, at that time? Maybe not since bread wheat as a species is only 8,500–9,000 years old (Avraham Levy & Moshe Feldman, The Plant Cell 34(7): 2549–2567, 2011; https://doi.org/10.1093/plcell/koac130); eelgrass (Zostera marina) [the seeds of which marine plant were possibly also eaten? See e.g. Mikael Fauvelle et al., Journal of California and Great Basin Anthropology 32(2): 187–195, 2012; http://www.jstor.org/stable/24644376; hops (Humulus lupulus) [maybe indicating ale was consumed? Probably not for this use since hops weren’t documented in connection with flavouring beer until many thousands of years later than the date of the pitch finds – in the 8^th (Simran Sethi; Helena Korpelainen & Maria Pietiläinen, Econ Bot 75: 302–322, 2021; https://doi.org/10.1007/s12231-021-09528-1) or 9^th century CE (Martyn Cornell); loblolly pine (Pinus taeda); Himalayan hornbeam (Carpinus viminea); and African oil palm (Elaeis guineensis) [common and scientific names as extracted from Tables 7 – 11 in the paper’s Supplementary Material].

However, whilst the last named species is an intriguing find in a site far to the north of where you’d expect the oil palm to grow – and raises some interesting questions about how it got to Sweden – probably the most surprising find is what’s not on that list. Although Jensen et al. explicitly tell us that birch is the source of the pitch they examined, there is no mention that they found any birch [Betula sp. (Gareth Davies)] DNA in their article [or in the paper’s Supplementary Material]. Why isn’t it mentioned? Was the pitch prepared – or chewed – so thoroughly that all traces of birch DNA were removed or destroyed? Or was the pitch derived from a non-birch source? Now, that notion is intriguing.

If you’re getting a feeling of déjà vu at this stage, that may be because this work has some similarities with a study of Danish teenager’s gum by Theis Jensen et al. (Nat Commun 10, 5520 (2019); https://doi.org/10.1038/s41467-019-13549-9). In that study, they sampled 5,700-year-old chewed birch pitch associated with an individual in Denmark. They extracted sufficient ancient human DNA to determine that the pitch-chewer was female [christened ‘Lola’, her artistically-interpreted image is shown above] and genetically more closely related to western hunter-gatherers from mainland Europe than hunter-gatherers from central Scandinavia. Amongst the non-human DNA from the sample, they identified birch (Betula pendula) and ‘hazelnut’ (Corylus avellana), and mallard (Anas platyrhynchos) [the last two were also identified in the work of Kırdök et al. on Swedish pitch considered above].

Although the presence of birch DNA was considered to be from the source of the pitch, and not therefore a food item, Jensen et al. proposed that the hazelnut and mallard may have come from a recent meal. The results highlight the potential of chewed birch pitch as a source of ancient DNA, which can provide information about the genetic heritage of individuals as well as diet, etc. [as was also gleaned by Kırdök et al. in the ancient DNA they extracted from even older Swedish material in the previous study considered in this post]. For a scicomm version of Theis Jensen et al‘s work, see Brian Handwerk‘s article, and, for a UK national newspaper’s version, see Ian Sample’s story. [And for how human DNA in gum has been exploited artistically, see And, finally in Part 2 of a deep dive into chewing-gum].

[For more on chewing-gum, don’t forget Part 2 of this deep dive into the topic, the next post.]

* Here Mr P Cuttings is distinguishing ‘chewing-gum’, the chewy product, from ‘chewing gum’, the act of masticating the chewy product…

** Although the gum in 21^st century chewing-gum may have little in it by way of plant-derived material (Len Fisher; Bethan Grylls), modern-day – dating from the 1860s – chewing-gum was made from chicle (Keith Pandolfi). But, long before that, chicle, “gum that consists of the coagulated milky latex of the sapodilla tree (Manilkara zapota)”, was chewed by the ancient Mayan and Aztec peoples (Elizabeth Nix). With those long-established botanical credentials as a precedent, Mr P Cuttings considers chewing-gum to be a legitimate plants-and-people topic for a post on the blog.

*** Mr Cuttings always finds it amusing that gum can be good for the health of one’s gums – the soft tissue that covers the base of the teeth. But that’s the trouble/thing with the English language. Although it may have 171,476 words per the Oxford English Dictionary, (or 470,000, and maybe up to 1,022,000 words according to other sources), it doesn’t have enough unique ones to distinguish between what sort of ‘gum’ one is talking about.

**** As you might have expected, this study was widely covered in the science news – each source often having a slightly different ‘take’ on the story, as suits its target audience. So, for more to get your teeth into on this topic, and in – usually – a more-user-friendly narrative than the original scientific article, see here, and articles by Olivia Young, Dario Radley, Michael Franco, Ben Taub, Rory Boothe, and Will Sullivan. And for the inside story of the investigation by two of the researchers involved, see the article by Anders Götherström & Emrah Kırdök.

***** Mr Cuttings wonders. If mistletoe was used as an arrow poison, as Kırdök et al suggest, is it conceivable that the poisonous material could be mixed into the birch pitch directly. Then, when the pitch was chewed – assuming it wasn’t swallowed an potentially poisoned the chewer – and softened, the poison-infused adhesive could be used to secure the arrowhead to the shaft of the arrow. That way, poison is close enough to the arrowhead that it can be introduced into the wounded prey, but with the advantage that poison isn’t coating the sharp arrowheads so that it could be accidentally introduced into the blood stream of the archer. Just a thought. [Followers of Norse mythology will probably now be thinking of the arrow made from mistletoe that was used by blind god Hother to kill Balder when tricked into doing so by Loki (e.g. here, here, and here].