Origins of Agriculture: an Ecological Perspective on Crop Domestication

这项研究旨在开发一种新的作物驯化生态模型，在考古记录的约束下，整合环境变化、植物特性和人类因素的作用。它阐述了自然选择和人类机构在农业出现的不同阶段发挥了关键作用的观点，侧重于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。我们提出了一个并行的实验和考古植物学工作包的研究计划，将巩固开发和完善这一新模型所需的证据。我们的生态模型是在考古文献记载的农业逐步广泛起源的框架内制定的，并基于这样的命题，即在从采集到耕作的不同阶段，不同的“驯化综合症”元素独立出现。特别是，它区分了考古上可见的两个驯化特征：较大的颗粒尺寸和种子不裂，并将其视为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，对有限范围的大种子物种的专门化，以及在这些物种中选择更大的种子，都是由人类饮食选择和生态过程之间的相互作用推动的。我们的中心论点是，种子大小与一系列功能特征相关，这些特征通过生态过程有利于某些物种作为农作物，并通过进化过程选择这些作物物种的大种子基因类型。我们通过讨论沿着更大的封建主义和农业的道路上的四个假设阶段来推进该模型。先前的研究表明，在考古植物学记录中，至少有两个阶段可以通过代表采集种子的野生群落或杂草组合的非食用物种的存在来识别。考古植物学的经验证据，包括不同时期的植物光谱、颗粒大小和生态条件，将被用来评估拟议模型解释观察到的变化的可行性。建立农业前和早期农业遗址的考古植物学数据库，并对这些记录进行量化分析，将确定(A)可能被故意收集作为食用植物的物种的范围，并提供采集的生态背景，(B)随着作物祖先物种的出现，植物谱变窄的程度、地理位置和日期，以及(C)潜在杂草群落的出现。将对野生(作物祖先和其他谷物物种)和驯化的谷物和豆类作物的粒度测量进行分析，以确定种子大小何时(就作物而言)以及是否(就野生谷物而言)增大，以及与相关的非食用植物物种组合的变化有关的时间，特别是与首次发现潜在杂草组合之前的二氧化碳水平或气候变化有关的变化。同时，生态学实验将通过测试有关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)对生态条件变化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类型与二氧化碳水平上升的关系，与上一次冰河时代结束时的二氧化碳水平相当，以及与干扰程度更高、肥力更高的人类产生的微环境的关系。

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.