Chris J. Stevens

Convergent evolution and parallelism in plant domestication revealed by an expanding archaeological record

Significance Agriculture was a transformative development in the history of human societies and natural environments and drove the evolution of new domesticated species. Crop plants are the predominant domesticated species in most agricultural systems and are an essential component in all the food production systems that underpinned the development of urban societies. Archaeological plant remains provide a range of insights into the processes by which plants were domesticated in different parts of the world. The present paper provides a unique synthesis of evidence, including quantitative evidence on the trajectory and rate of domestication in seed crops and patterns in the development of tropical vegetatively propagated crops. Recent increases in archaeobotanical evidence offer insights into the processes of plant domestication and agricultural origins, which evolved in parallel in several world regions. Many different crop species underwent convergent evolution and acquired domestication syndrome traits. For a growing number of seed crop species, these traits can be quantified by proxy from archaeological evidence, providing measures of the rates of change during domestication. Among domestication traits, nonshattering cereal ears evolved more quickly in general than seed size. Nevertheless, most domestication traits show similarly slow rates of phenotypic change over several centuries to millennia, and these rates were similar across different regions of origin. Crops reproduced vegetatively, including tubers and many fruit trees, are less easily documented in terms of morphological domestication, but multiple lines of evidence outline some patterns in the development of vegecultural systems across the New World and Old World tropics. Pathways to plant domestication can also be compared in terms of the cultural and economic factors occurring at the start of the process. Whereas agricultural societies have tended to converge on higher population densities and sedentism, in some instances cultivation began among sedentary hunter–gatherers whereas more often it was initiated by mobile societies of hunter–gatherers or herder–gatherers.

Domestication as innovation: the entanglement of techniques, technology and chance in the domestication of cereal crops

Abstract The origins of agriculture involved pathways of domestication in which human behaviours and plant genetic adaptations were entangled. These changes resulted in consequences that were unintended at the start of the process. This paper highlights some of the key innovations in human behaviours, such as soil preparation, harvesting and threshing, and how these were coupled with genetic ‘innovations’ within plant populations. We identify a number of ‘traps’ for early cultivators, including the needs for extra labour expenditure on crop-processing and soil fertility maintenance, but also linked gains in terms of potential crop yields. Compilations of quantitative data across a few different crops for the traits of non-shattering and seed size are discussed in terms of the apparently slow process of domestication, and parallels and differences between different regional pathways are identified. We highlight the need to bridge the gap between a Neolithic archaeobotanical focus on domestication and a focus of later periods on crop-processing activities and labour organization. In addition, archaeobotanical data provide a basis for rethinking previous assumptions about how plant genetic data should be related to the origins of agriculture and we contrast two alternative hypotheses: gradual evolution with low selection pressure versus metastable equilibrium that prolonged the persistence of ‘semi-domesticated’ populations. Our revised understanding of the innovations involved in plant domestication highlight the need for new approaches to collecting, modelling and integrating genetic data and archaeobotanical evidence.

Did Neolithic farming fail? The case for a Bronze Age agricultural revolution in the British Isles

This paper rewrites the early history of Britain, showing that while the cultivation of cereals arrived there in about 4000 cal BC, it did not last. Between 3300 and 1500 BC Britons became largely pastoral, reverting only with a major upsurge of agricultural activity in the Middle Bronze Age. This loss of interest in arable farming was accompanied by a decline in population, seen by the authors as having a climatic impetus. But they also point to this period as the time of construction of the great megalithic monuments, including Stonehenge. We are left wondering whether pastoralism was all that bad, and whether it was one intrusion after another that set the agenda on the island.

Between China and South Asia: A Middle Asian corridor of crop dispersal and agricultural innovation in the Bronze Age

The period from the late third millennium BC to the start of the first millennium AD witnesses the first steps towards food globalization in which a significant number of important crops and animals, independently domesticated within China, India, Africa and West Asia, traversed Central Asia greatly increasing Eurasian agricultural diversity. This paper utilizes an archaeobotanical database (AsCAD), to explore evidence for these crop translocations along southern and northern routes of interaction between east and west. To begin, crop translocations from the Near East across India and Central Asia are examined for wheat (Triticum aestivum) and barley (Hordeum vulgare) from the eighth to the second millennia BC when they reach China. The case of pulses and flax (Linum usitatissimum) that only complete this journey in Han times (206 BC–AD 220), often never fully adopted, is also addressed. The discussion then turns to the Chinese millets, Panicum miliaceum and Setaria italica, peaches (Amygdalus persica) and apricots (Armeniaca vulgaris), tracing their movement from the fifth millennium to the second millennium BC when the Panicum miliaceum reaches Europe and Setaria italica Northern India, with peaches and apricots present in Kashmir and Swat. Finally, the translocation of japonica rice from China to India that gave rise to indica rice is considered, possibly dating to the second millennium BC. The routes these crops travelled include those to the north via the Inner Asia Mountain Corridor, across Middle Asia, where there is good evidence for wheat, barley and the Chinese millets. The case for japonica rice, apricots and peaches is less clear, and the northern route is contrasted with that through northeast India, Tibet and west China. Not all these journeys were synchronous, and this paper highlights the selective long-distance transport of crops as an alternative to demic-diffusion of farmers with a defined crop package.

Modelling the Geographical Origin of Rice Cultivation in Asia Using the Rice Archaeological Database

We have compiled an extensive database of archaeological evidence for rice across Asia, including 400 sites from mainland East Asia, Southeast Asia and South Asia. This dataset is used to compare several models for the geographical origins of rice cultivation and infer the most likely region(s) for its origins and subsequent outward diffusion. The approach is based on regression modelling wherein goodness of fit is obtained from power law quantile regressions of the archaeologically inferred age versus a least-cost distance from the putative origin(s). The Fast Marching method is used to estimate the least-cost distances based on simple geographical features. The origin region that best fits the archaeobotanical data is also compared to other hypothetical geographical origins derived from the literature, including from genetics, archaeology and historical linguistics. The model that best fits all available archaeological evidence is a dual origin model with two centres for the cultivation and dispersal of rice focused on the Middle Yangtze and the Lower Yangtze valleys.

Holocene fluctuations in human population demonstrate repeated links to food production and climate

Significance The relationship between human population, food production, and climate change is a pressing concern in need of high-resolution, long-term perspectives. Archaeological radiocarbon dates have increasingly been used to reconstruct past population dynamics, and Britain and Ireland provide both radiocarbon sampling densities and species-level sample identifications that are globally unrivalled. We use this evidence to demonstrate multiple instances of human population downturn over the Holocene that coincide with periodic episodes of reduced solar activity and climate reorganization as well as societal responses in terms of altered food-procurement strategies. We consider the long-term relationship between human demography, food production, and Holocene climate via an archaeological radiocarbon date series of unprecedented sampling density and detail. There is striking consistency in the inferred human population dynamics across different regions of Britain and Ireland during the middle and later Holocene. Major cross-regional population downturns in population coincide with episodes of more abrupt change in North Atlantic climate and witness societal responses in food procurement as visible in directly dated plants and animals, often with moves toward hardier cereals, increased pastoralism, and/or gathered resources. For the Neolithic, this evidence questions existing models of wholly endogenous demographic boom–bust. For the wider Holocene, it demonstrates that climate-related disruptions have been quasi-periodic drivers of societal and subsistence change.

Geographic mosaics and changing rates of cereal domestication

Domestication is the process by which plants or animals evolved to fit a human-managed environment, and it is marked by innovations in plant morphology and anatomy that are in turn correlated with new human behaviours and technologies for harvesting, storage and field preparation. Archaeobotanical evidence has revealed that domestication was a protracted process taking thousands of plant generations. Within this protracted process there were changes in the selection pressures for domestication traits as well as variation across a geographic mosaic of wild and cultivated populations. Quantitative data allow us to estimate the changing selection coefficients for the evolution of non-shattering (domestic-type seed dispersal) in Asian rice (Oryza sativa L.), barley (Hordeum vulgare L.), emmer wheat (Triticum dicoccon (Shrank) Schübl.) and einkorn wheat (Triticum monococcum L.). These data indicate that selection coefficients tended to be low, but also that there were inflection points at which selection increased considerably. For rice, selection coefficients of the order of 0.001 prior to 5500 BC shifted to greater than 0.003 between 5000 and 4500 BC, before falling again as the domestication process ended 4000–3500 BC. In barley and the two wheats selection was strongest between 8500 and 7500 BC. The slow start of domestication may indicate that initial selection began in the Pleistocene glacial era. This article is part of the themed issue ‘Process and pattern in innovations from cells to societies’.

Comparing subsistence strategies in different landscapes of North China 10,000 years ago:

A recent switch in the study of the beginning of agriculture is to demonstrate the increasingly closer interaction between people and the landscape and how this would have played a crucial role in the transition to agriculture. Understanding the palaeo-ecology of the local environments at key sites and its relationship with subsistence strategies is critical to an improved appreciation of such interactions. This article examines macro- and micro-plant remains discovered at two important sites in North China, both dated to around 10,000 cal. yr BP. These two sites, Zhuannian and Nanzhuangtou, are located on the terrace of the Bai River in the Yan Mountains and next to Baiyangdian Lake on the piedmont of the Taihang Mountains, respectively. The floral remains at these two sites provide a great opportunity to examine (1) post-Pleistocene subsistence strategies, (2) the increasing consumption of millets and grassy plants and its significance and (3) the intra-regional diversity in food exploitation and its relationships with local environments. While the macro-plant remains at Nanzhuangtou indicate the importance of aquatic plants in the palaeo-diet, those at Zhuannian suggest a tendency of exploiting tree plants. This significance of these diversified plant food exploitation strategies by the last hunter-gatherers should be paid more attention in future research. Our data also once again confirm the importance of millet consumption to these hunter-gatherers on the eve of millet domestication.

Alternative strategies to agriculture: the evidence for climatic shocks and cereal declines during the British Neolithic and Bronze Age (a reply to Bishop)

Abstract Our suggestion that agriculture was temporarily abandoned for several centuries throughout much of mainland Britain after 3600 BC has provoked criticism, notably the claim by Bishop (2015) that we have missed continuity in Scotland. We demonstrate that firm evidence for widespread agriculture within the later Neolithic is still unproven. We trace the disappearance of cereals and the associated population collapse to a probable climatic shift that impacted the abundance of rainfall and lowered temperatures, thus affecting the reliability of cereals. Divergent strategies and patterns are identified on the Scottish Islands versus the mainland, which has more in common with England, Wales and Ireland. We argue that climate shocks disrupt existing subsistence patterns, to which varied responses are represented by divergent island and mainland patterns, both in the Late Neolithic and during the Early and Middle Bronze Age. Favourable climates encouraged population growth and subsistence innovation, such as at the start of the Neolithic and in the Beaker period.

Evidence for Sorghum Domestication in Fourth Millennium BC Eastern Sudan: Spikelet Morphology from Ceramic Impressions of the Butana Group

Since the 1970s, the quest for finding the origins of domesticated sorghum in Africa has remained elusive despite the fact that sorghum (Sorghum bicolor (L.) Moench. sensu stricto) is one of the world’s most important cereals. Recognized as originating from wild populations in Africa (Sorghum arundinaceum (Desv.) Stapf), however, the date and cultural context of its domestication has been controversial, with many scholars inferring an early Holocene origin in parallel with better-known cereal domestications. This paper presents firm evidence that the process of domesticating sorghum was present in the far eastern Sahel in the southern Atbai at an archaeological site associated with the Butana Group. Ceramic sherds recovered from excavations undertaken by the Southern Methodist University Butana Project during the 1980s from the largest Butana Group site, KG23, near Kassala, eastern Sudan, were analyzed, and examination of the plant impressions in the pottery revealed diagnostic chaff in which both domesticated and wild sorghum types were identified, thus providing archaeobotanical evidence for the beginnings of cultivation and emergence of domesticated characteristics within sorghum during the fourth millennium BC in eastern Sudan.