Ancient growers: The archaeological secrets of crop domestication
Crop domestication represents a significant turning point in the advancement of societies, as systematic food production at scale could sustain large populations through integrated agricultural networks, which allowed for the development of more complex societies and communities. By domesticating crops, societies could improve their harvest yields and manage their food surpluses to ensure food security. This paper will contend that archaeological evidence for crop domestication falls into one of three primary mechanisms, namely crop selection and modification, genetic evidence and cultural artifacts, and will propose that these three mechanisms provide fundamental processes for archaeologists to identify the origins of crop domestication.
Crop selection and modification
Crop selection, or the identification and deliberate cultivation of crop species which could provide scalable yields of edible plants, is a key mechanism for verifying the archaeological evidence for crop domestication. Evidence of specific crop selection shows that specific societies were able to identify the appropriate species to grow and domesticate at scale.
Zheng et al (2016) analysed evidence from China’s Lower Yangtze valley, where Oryza sativa spikelet bases were recovered during the period 9000–8400 BC, to provide evidence of crop selection. Among the spikelet bases, a significantly larger quantity were found to have been of non-shattering rice, which would have been a more durable species suited to systematic cultivation than wild and intermediate species of shattering rice (Zheng et al, 2016). This observation was supported by archaeological evidence in dig sites in Liangzhu (5300–4200 BC), Majiabang (6300–6000 BC) and Tianluoshan (7000–6500 BC), suggesting widespread prevalence of non-shattering rice crop domestication during various Chinese dynasties (Zheng et al, 2016).
Deliberate human selection of larger seeds was also found in early cave habitats, when archaeologists observed that a specific cave squash species (Cucurbita pepo) was far larger than normal Cucurbita gourds in the wild (Zeder et al, 2006).This was also present in the species C. berlandieri ssp. Jonesianum, which exhibited a smaller seed coat thickness than its wild version, C. berlandieri ssp. Berlandieri, suggesting evidence of intentional selection and domestication in order to improve growth rates and yield of the crop (Zeder et al, 2006).
Finally, researchers have been able to study the overall pattern of biodiversity of species in a region as evidence of crop selection. Generally, as crops are domesticated, a declining pool of species will be aggressively cultivated to become the majority of crops in a region (Begun, 2013). This provides clear archaeological evidence for deliberate crop selection and cultivation.
Genetic evidence
Genetic analysis techniques, such as genomic sequencing, have also contributed to archaeological evidence for crop domestication over different periods of time. Paris (2016) demonstrated how the Cucurbitaceae gourd family, comprising sundry crops such as pumpkins, melons and watermelons, started being cultivated in the Americas over 10,000 years prior with the introduction of Cucurbita spp (the squash). This was followed by watermelons 4,000 years prior in northeast Africa, and the later spread of all gourd species to Europe and Africa in the 15th century (Paris, 2016). By sequencing the genetic profile of plant cultivars found in these regions at dig sites, archaeologists are able to identify the accurate ancestral origins of Cucurbitaceae (Paris, 2016).
Kantar et al (2017) discuss how the processes of crop selection to alter plant phenotypes, and conscious cross-breeding and cultivation, have been shown to leave genetic markets in plant species over time, which emerge when researchers use techniques such as population genomic profiling to infer patterns of crop ancestry (Kantar et al, 2017). These phenotypic traits may emerge in the form of lower shattering rates, lower lateral branching rates, and faster flowering times, which contribute to increased agricultural yield and ease of cultivation. By tracing the ancestry of crop species genetic profiles, researchers can identify the pattern of crop cultivation accordingly (Kantar et al, 2017).
Cultural artifacts
Cultural artifacts, such as artwork, pots, urns and storage vessels, have also proven to be a valuable repository of archaeological evidence for crop domestication. Such cultural artifacts have served as evidence for direct crop cultivation and storage, while residues on these artifacts have been successfully tested to provide archaeological evidence of cultivation of specific species. In Egypt and Africa c. 4,000–5,000 BC, images of Citrullus lanatus seeds were found to be portrayed as vegetables, indicating an awareness of their cultivation value (Paris, 2016). Pottery artifacts in the Southeast Ecuadorian Santa Ana-La Florida (SALF) site were also found to have traces of Theobroma cacao, allowing archaeologists to date cocoa crop cultivation to 1,500 years in South America prior to the spread of cocoa to Central America (Zarillo et al, 2018). The SALF site thus served as archaeological evidence that allowed archaeologists to dispute the widely held belief of cocoa’s origin in Central America and Mesoamerica (Zarillo et al, 2018).
Furthermore, fragments of ceramic pottery provided artwork of domesticated sorghum (Sorghum bicolor), allowing for archaeologists to date the cultivation of sorghum to the eastern Sudan Sahel region (Winchell et al, 2017). Cultural artifacts found by archaeologists studying the Roman Andalusia period in Italy were also able to compare characteristics of seeds and fruits to identify cultivated and domesticated species, such as mesocarps, cereals and pulses of olives, which were used for food (Voropaeva and Stika, 2018). These cultural artifacts therefore provide rich evidence to support the case for development of crop domestication in a region.
Ongoing debates on the archaeological evidence for crop domestication
Langlie et al (2014) discuss a number of research issues that raise disputes on the causes, geographic origins and timing of crop domestication. For example, limited or contaminated archaeological evidence has led to errors in the identification of origin centres for crop cultivation. This may arise as the result of evidence contamination or forgeries. Archaeologists have also made errors on the pace and geographic spread of the cultivation of specific crops (Langlie et al, 2014). These errors have been gradually addressed through the use of DNA analysis and ethnographic techniques to assign more accurate chronological sequences to understand the context of crop cultivation (Langlie et al, 2014).
Concurrently, emerging tools such as phytolith and DNA analysis have emerged to compensate for the shortcomings of existing methods, but have not been without controversy themselves. Phytolith analysis has allowed archaeologists and anthropologists to understand crop domestication in the context of past diets, but has been criticized for its inconsistent morphological criteria and its lack of standardisation in research processes (Shillito, 2013). Similarly, DNA analysis has been subject to criticism due to the natural variations in crop genetics profiled over time, which may not be representative of the genetic profile of the original crop cultivated in past societies (Langlie et al, 2014).
Conclusion
The archaeological evidence for crop domestication remains an emerging field with significant debate. While crop selection and modification, genetic evidence and cultural artifacts provide fundamental mechanisms for archaeologists to identify the origins of crop domestication, these mechanisms are occasionally subject to error. For example, plant species residues may decompose over time compared to tools and animal bones, while contamination of specimens can lead to erroneous conclusions on the origins of domesticated species. Nonetheless, these mechanisms provide detailed evidence that help archaeologists and anthropologists to chart the development of food cultivation and agriculture in the early human population. As human societies evolved, the selection and domestication of crops led to a fall in crop biodiversity and a rise in abundance of high-yield crops. This suggests that the patterns of early crop domestication were based primarily on the selective breeding of crops suitable for large scale agriculture, which proves that early human populations had limited but viable means of selecting crops in order to generate high agricultural yields.
