Simon Fitch

Sedimentary DNA from a submerged site reveals wheat in the British Isles 8000 years ago

Early wheat movement into Britain The transition into the New Stone Age, or Neolithic period, in Great Britain and Europe was characterized by a change from hunter-gatherers to farmers. However, the early stages of this transition are not well understood. Smith et al. studied archaeological remains at an 8000-year-old site that has been underwater ever since the Neolithic (see the Perspective by Larson). The finds include evidence of wheat (or a relative of wheat) 2000 years before the first documented farmers in Britain. It seems that trade may have preceded the adoption of farming. Science, this issue p. 998; see also p. 945 Wheat was being consumed in Britain 2000 years earlier than expected. [Also see Perspective by Larson] The Mesolithic-to-Neolithic transition marked the time when a hunter-gatherer economy gave way to agriculture, coinciding with rising sea levels. Bouldnor Cliff, is a submarine archaeological site off the Isle of Wight in the United Kingdom that has a well-preserved Mesolithic paleosol dated to 8000 years before the present. We analyzed a core obtained from sealed sediments, combining evidence from microgeomorphology and microfossils with sedimentary ancient DNA (sedaDNA) analyses to reconstruct floral and faunal changes during the occupation of this site, before it was submerged. In agreement with palynological analyses, the sedaDNA sequences suggest a mixed habitat of oak forest and herbaceous plants. However, they also provide evidence of wheat 2000 years earlier than mainland Britain and 400 years earlier than proximate European sites. These results suggest that sophisticated social networks linked the Neolithic front in southern Europe to the Mesolithic peoples of northern Europe.

Thermal age, cytosine deamination and the veracity of 8,000 year old wheat DNA from sediments

Recently, the finding of 8,000 year old wheat DNA from submerged marine sediments (1) was challenged on the basis of a lack of signal of cytosine deamination relative to three other data sets generated from young samples of herbarium and museum specimens, and a 7,000 year old human skeleton preserved in a cave environment (2). The study used a new approach for low coverage data sets to which tools such as mapDamage cannot be applied to infer chemical damage patterns. Here we show from the analysis of 148 palaeogenomic data sets that the rate of cytosine deamination is a thermally correlated process, and that organellar generally shows higher rates of deamination than nuclear DNA in comparable environments. We categorize four clusters of deamination rates (α,β,γ,ε) that are associated with cold stable environments, cool but thermally fluctuating environments, and progressively warmer environments. These correlations show that the expected level of deamination in the sedaDNA would be extremely low. The low coverage approach to detect DNA damage by Weiss et al. (2) fails to identify damage samples from the cold class of deamination rates. Finally, different enzymes used in library preparation processes exhibit varying capability in reporting cytosine deamination damage in the 5’ region of fragments. The PCR enzyme used in the sedaDNA study would not have had the capability to report 5’ cytosine deamination, as they do not read over uracil residues, and signatures of damage would have better been sought at the 3’ end. The 8,000 year old sedaDNA matches both the thermal age prediction of fragmentation, and the expected level of cytosine deamination for the preservation environment. Given these facts and the use of rigorous controls these data meet the criteria of authentic ancient DNA to an extremely stringent level.

Response to Comment on “Sedimentary DNA from a submerged site reveals wheat in the British Isles 8000 years ago”

Bennett questions the rigor of the dating of our sample from which sedimentary ancient DNA was obtained and the reliability of the taxonomic identification of wheat. We present a further radiocarbon date from S308 that confirms the lateral consistency of the palaeosol age. The suggestion of taxonomic false positives in our data illustrates a misinterpretation of the phylogenetic intersection analysis.

Time and Tide: Modelling the Effects of Landscape Change on Population Support in the Southern North Sea

The submerged landscape of the North Sea has long been known by archaeologists as an area of Mesolithic occupation yet, despite this, the nature of the occupation of this landscape has remained poorly understood due to its inaccessibility. This chapter presents a first attempt to use digital technologies and modelling to understand the nature of the human occupation of these currently inaccessible landscapes and their associated demography. The models aim to explore the impacts of sea level-driven landscape change upon the Mesolithic population, and further aims to reveal the diversity of resources that would have been present. As such the model will seek to take the first steps in developing an adequate representation of the past landscape and generate an understanding into how past landscape evolution may have served as a buffer to the effects of marine inundation.