WEWeb EcologyWEWeb Ecol.1399-1183Copernicus PublicationsGöttingen, Germany10.5194/we-16-1-2016The first shoots of a modern morphometrics approach to the origins of
agricultureBonhommeV.v.bonhomme@sheffield.ac.ukForsterE.WallaceM.StillmanE.CharlesM.JonesG.School of Mathematics and Statistics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UKUMR 5554 Institut des Sciences de l'Evolution, équipe Dynamique de la
biodiversité, anthropo-écologie, Université de Montpellier, CNRS, IRD, EPHE Place Eugène Bataillon, 34095 Montpellier, CEDEX 05, FranceDepartment of Archaeology, University of Sheffield, Northgate House, West Street, Sheffield S1 4ET, UKInstitute of Archaeology, 36 Beaumont St, Oxford, OX1 2PG, UKV. Bonhomme (v.bonhomme@sheffield.ac.uk)18January20161611212October20154December20159December2015This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://we.copernicus.org/articles/16/1/2016/we-16-1-2016.htmlThe full text article is available as a PDF file from https://we.copernicus.org/articles/16/1/2016/we-16-1-2016.pdfIntroduction
The transition from a mobile hunter-gatherer lifestyle to one of settled
agriculture is arguably the most fundamental change in the development of
human society (Lev-Yadun et al., 2000). The establishment of agricultural
economies, emerging initially in the Fertile Crescent of the Near East
(Nesbitt, 2002), required the domestication of crops; ancient plant remains
recovered from early farming sites provide direct evidence for this process
of domestication. Archaeobotanical remains are typically preserved through
charring (partial to complete carbonisation through exposure to heat) and
recovered during archaeological excavation (Charles et al., 2015). Seeds of the same
species, recovered from different sites and periods, can sometimes be seen
to exhibit morphological differences, which may have arisen owing to
variations in cultivation practices, climate, soils and altitude, etc. To
explore these possibilities, morphological variation in seeds of wheat and
barley between archaeological sites was recorded and mapped both in time and
space. Results presented here suggest that modern morphometric approaches
may help to test some long-debated hypotheses and pave the way for new
insights into the evolutionary origins of agriculture in western Asia.
Material and methods
Grains of the “primitive” glume wheats einkorn (Triticum monococcum) and emmer (T. dicoccum), domesticated
barley (Hordeum vulgare) and their wild progenitors (T. boeoticum, T. dicoccoides and H. spontaneum respectively), dating from
ca. 13 000 to 9000 years before present, originating mainly from the Fertile
Crescent region and now archived in various European institutions, were
sampled. Three orthogonal views were photographed and grain outlines were
converted into x–y coordinates. The three views of each grain were
processed independently and later combined for analysis. Traditional
measurements were obtained directly (length, breadth, thickness) or
estimated (ellipsoid volume) based on these outlines. Outlines were then
centred, scaled and aligned, and elliptical Fourier transforms were
calculated (Kuhl and Giardina, 1982). The number of harmonics was chosen to
encompass 99 % of the harmonic power for each view. Elliptical Fourier
transforms turned the grain shapes into quantitative variables that were
further treated using classical multivariate approaches, mainly ordination
and classification. All calculations and analyses were accomplished using
the R environment (R Development Core Team, 2015) and the modern
morphometrics package Momocs (Bonhomme, 2015; Bonhomme et al., 2014). Linear
discriminant analyses were performed with the MASS package (Venables and
Ripley, 2015).
(a) Map of the archaeological sites along with their sample sizes.
(b) The increasing trend for the grain volume observed in emmer and einkorn
grains. The regression indicates a 50 % increase in the grain volume over
5000 years. (c) The first two axes of the principal component
analysis (∼ 70 % of the total variance) along with
confidence ellipses labelled with taxon names and, in the background, a
morphospace of the reconstructed shapes with the three views arranged as
dorsal above, lateral left and polar right. The red ensemble on the left
gathers all Hordeum taxa; the blue/green ellipses are all Triticum taxa.
Results and discussion
A total of 1378 grains were photographed in three orthogonal views, with 554
being of the genus Hordeum and 824 from Triticum. Grains were sampled from 14 prehistoric
archaeological sites across southwest Asia (Fig. 1a). This, to our
knowledge, is the largest photographic database of ancient grains ever
collected. Increase in grain size has previously been associated with
domestication of cereals (e.g. Fuller et al., 2011), and this trend can be seen
clearly in our data set. For instance, for einkorn and emmer grains there is a
50 % increase in volume between 10 000 and 5000 BC when considering all sites
together (Fig. 1b).
Principal component analysis on the whole data set (Fig. 1c) illustrates
the difference between Hordeum and Triticum taxa. Cross-validation (leave-one-out) at the
genus level with a linear discriminant analysis suggests this can be
feasible with a high confidence level in the classification (95 and
98 % of correct attribution for Hordeum and Triticum grains, respectively). Whilst an
automated classification system remains some way off, such analyses may
prove a valuable tool for aiding the identification of crop remains by
archaeobotanists. Although it is unlikely that this would be used for the
most commonly identified taxa, morphometric analysis may help to separate
types that are difficult to distinguish by eye, such as wild and
domesticated forms of a species or taxa that are traditionally grouped as
indistinguishable (e.g. wild einkorn (Triticum boeoticum) and rye (Secale spp.)). For instance, 86 %
of wild and 75 % of domesticated einkorn (Triticum boeoticum and T. monococcum) grains are correctly
classified when species information is removed.
To conclude, these first results of a modern morphometric approach on the
largest photographic database of ancient grains ever collected are
promising, and they pave the way for exploration of changes in grain size and
shape through time and across geographic regions.
Acknowledgements
This research is funded by the European Research Council project
“Evolutionary origins of agriculture” PI: Glynis Jones, grant number
269030. This is publication ISEM 2015-254.
Edited by: D. Montesinos
Reviewed by: two anonymous referees
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