Origins of Agriculture: an Ecological Perspective on Crop Domestication

本研究的目的是在考古记录的约束下，综合环境变化、植物性状和人类活动的作用，建立一种新的作物驯化生态模型。它阐述了自然选择和人类能动性在农业出现的不同阶段发挥了关键作用的观点，重点是在完全农业社会之前的时期，植物、人类和环境之间的相互作用。我们提出了一个研究计划，包括平行的实验和考古工作包，将巩固必要的证据来发展和完善这个新模型。我们的生态模型是在考古记录的农业逐渐广泛起源的框架内制定的，并基于“驯化综合征”的不同要素在从采集到农业过渡的不同阶段独立出现的命题。特别地，它区分了两种考古学上可见的驯化特征：更大的颗粒尺寸和种子不开裂，并认为这些是驯化过程中不同阶段不同选择压力的结果。我们的重点是前者，我们认为，对有限范围内的大种子物种的专业化，以及对这些物种中较大种子大小的选择，都是由人类饮食选择和生态过程之间的相互作用驱动的。我们的中心论点是，种子大小与一系列功能性状相关，通过生态过程，这些性状有利于某些物种作为作物，而不是其他物种，并通过进化过程，选择这些作物物种的大种子基因型。我们通过讨论向更大的定居主义和农业发展的道路上的四个假设阶段来推进模型。先前的研究表明，这些阶段中至少有两个可以在考古植物学记录中通过非食物物种的存在来识别，这些物种要么代表采集种子的野生群落，要么代表杂草组合。以植物谱、粒度和不同时期的生态条件为形式的经验考古学证据将被用来评估所提出的模型解释观察到的变化的可行性。建立一个前农业和早期农业遗址的考古植物学数据库，并对这些记录进行定量分析，将确定(a)可能被故意作为食用植物收集的物种范围，并提供收集的生态背景；(b)随着作物祖先物种的突出，植物光谱缩小的程度、地理位置和日期；(c)潜在杂草群落的出现。将分析野生（作物祖先和其他谷物物种）和驯化谷物和豆类作物的粒度测量，以确定何时（在作物的情况下）和是否（在野生谷物的情况下）种子大小增加，以及其时间与相关非食用植物物种组合的变化有关，特别是与潜在杂草组合首次被识别之前的一段时间内二氧化碳水平或气候的变化有关。同时，生态实验将通过测试关于野生作物祖先和其他野生物种（以及作物祖先的大种子和小种子基因型）对变化的生态条件的差异反应的基本假设来评估模型中提出的变化机制的有效性。生态实验将确定植物物种和基因型与二氧化碳浓度升高（与上一个冰河期结束时的二氧化碳浓度升高相当）的关系，以及与人为造成的干扰程度更大、生育力更高的微环境的关系。

The proposed research aims to develop a new ecological model for crop domestication, integrating the roles of environmental change, plant traits, and human agency, under the constraints of the archaeological record. It addresses the idea that natural selection and human agency played a critical role at different stages in the emergence of agriculture, focusing on the interactions between plants, humans and environment during the period preceding fully agricultural societies. We propose a research programme with parallel experimental and archaeobotanical work packages that will consolidate the evidence necessary to develop and refine this new model. Our ecological model is formulated within the archaeologically documented framework of a gradual, widespread origin of agriculture, and is based on the proposition that different elements of the 'domestication syndrome' arose independently during different stages in the transition from gathering to farming. In particular it distinguishes the two archaeologically visible domestication traits: larger grain size and seed indehiscence, and sees these as consequences of different selective pressures operating at different stages in the domestication process. Our focus is on the former, and we argue that specialisation on a limited range of large-seeded species, and selection for larger seed size within these species, were both driven by an interaction between human diet choice and ecological processes. Our central thesis is that seed size correlates with a suite of functional traits which, through ecological processes, favour some species as crops over others and, through evolutionary processes, select for large-seeded genotypes of these crop species. We advance the model through the discussion of four hypothetical phases along the path towards greater sedentism and agriculture. Previous research has demonstrated that at least two of these phases can be recognized in the archaeobotanical record via the presence of non-food species representing either the wild communities from which seeds were gathered, or weed assemblages. Empirical archaeobotanical evidence, in the form of the plant spectrum, grain size and ecological conditions in different time periods will be used to assess the feasibility of the proposed model for explaining observed changes. The construction of an archaeobotanical database of pre-agricultural and early agricultural sites, and quantitative analysis of these records, will establish (a) the range of species likely to have been deliberately collected as food plants and provide the ecological context of gathering, (b) the extent, geographical locations, and date of the narrowing of the plant spectrum as the crop progenitor species came to prominence, and (c) the appearance of potential weed communities. Grain size measurements of both wild (crop progenitor and other grain species) and domesticated cereal and pulse crops will be analysed to establish when (in the case of crops) and whether (in the case of wild grains) seed size increased, and its timing in relation to changes in the associated non-food plant species assemblages, in particular in relation to changes in CO2 levels or climate during the period before potential weed assemblages are first recognized. At the same time, ecological experiments will assess the validity of the mechanisms of change proposed in the model by testing the underlying hypotheses concerning the differential responses of wild crop progenitors and other wild species (and of large and small-seeded genotypes of crop progenitors) to changing ecological conditions. Ecological experiments will determine the relationship of plant species and genotypes to increasing CO2 levels comparable to those occurring at the end of the last ice age, and to human-generated microenvironments with greater levels of disturbance and higher fertility.