Clear, standardized terms for the biological and cultural processes involved in the origins of agriculture worldwide remain elusive, despite considerable efforts to define them (Flannery 1973; Ford 1985; Harris 1989; Harris 1996a and b; Higgs 1972; Piperno and Pearsall 1998; Rindos 1984; Smith 1998; Smith 2001a; Zvelebil 1993; Zvelebil 1995; Zvelebil 1996). The reasons for inconsistencies in the treatment of terminology are several and tenacious because they are ultimately rooted in the nature of the problem itself. These include, but are not necessarily limited to the following: (1) research on domestication and agricultural origins is inherently a multi-disciplinary activity, and as such, a wide-ranging set of specialists have worked on the problem, each emphasizing definitions that are somewhat parochial; (2) historical change in each research tradition of archaeology, botany, and genetics has resulted in a range of definitions that may have been suitable at the time they were conceived but now add to the confusion; (3) rapidly expanding empirical knowledge and the characterization of local developmental sequences results in specialized language that does not transfer well to other regions where similar transformations occurred; (4) agricultural origins are an inherently evolutionary question and, as in any system of descent with modification, categorical or taxonomic distinctions have fuzzy and, for different cases, unevenly and perhaps differently demarcated boundaries; and, (5) food production and agriculture have an impact on multiple features of human societies—e.g., economic, political, social, and ideological, any one of which might be featured in definitions.

Like earlier attempts, our definitions reflect limitations of our knowledge and approach. Hunting and gathering entails obtaining daily sustenance through the collection or pursuit of wild foods; wild foods in turn being species whose reproduction and subsistence are not directly managed by humans. Data from around the world indicate that prior to approximately thirteen thousand years ago, all people known archaeologically relied upon hunting and gathering wild foods. Hunting and gathering populations expanded into a broad range of habitats during the Terminal Pleistocene and Early Holocene when foraging strategies diversified (Stiner 2001), in part due to the extinction of previously targeted, large-game species, but also because of the broad array of resource alternatives afforded by warmer Holocene climates (Richerson et al. 2001). Hunting and gathering societies have persisted in various parts of the world (Lee and Daly 1999), but starting after about 13,000 BP (before the present) most foragers evolved into or were subsumed or replaced by groups practicing mixed foraging and cultivation strategies and, ultimately, agriculture (Diamond and Bellwood 2003).

On the other end of a mixed spectrum of subsistence strategies is agriculture. We define agriculture as the near total reliance upon domesticated plants or animals; domesticates being varieties or species whose phenotype is a product of artificial selection by humans, and whose reproduction and subsistence are managed directly by people. For plants, such management almost always involves an investment in seed selection; clearing, systematic soil tillage, terracing to prepare fields, crop maintenance, weeding, fertilization, and other crop maintenance; and, development of infrastructure and facilities from irrigation canals to processing facilities and storage bins. Parallel efforts are entailed in animal husbandry. Even societies practicing the most intensive forms of agriculture may engage in incidental hunting and gathering of wild foods, depending upon their availability or desirability (e.g., deer, blackberries). Dense populations and centralized state-level societies like our own depend upon increasingly complex systems of agriculture (Boserup 1965; Zeder 1991) involving modification to soil texture, structure and fertility (Harris 1989) and sometimes resulting in severe environmental degradation, one of the great challenges of our day (Stockstad and Vogel 2003).

Our definition of agriculture emphasizes domesticated plants and animals. Domesticates are new plant or animal varieties or species created from existing wild species through incidental or active selection by humans (Smith 1998). Typically selection leads to biological characteristics that are advantageous to humans; larger seeds, thinner seed coats, greater docility, smaller size animals. Because humans intervene in the natural lifecycle of these plants and animals, many domesticates loose their ability to survive without human management. This outcome is not surprising since it is well known that foragers alter the landscape that they inhabit by burning, transferring plants and animals between habitats, and occasionally interjecting themselves into other species' lifecycles (Hastorf 1999; Smith 1998).

Some plant species were better suited to domestication than others due to their ability to do well in the artificial environments created by humans (Smith 1998). In some instances, the biological changes may have begun incidentally as a co-evolutionary by-product of human exploitation

(Rindos 1984). In other cases domestication may have occurred under conditions of repeated cultivation and harvest (Harlan 1992c; Harris 1989; Ford 1985; Piperno and Pearsall 1998). Cultivation is the tending of plants, wild or domesticated; husbandry is the parallel term for animal species. Use of the term cultivation specifically acknowledges the possibility that humans tended wild plants for significant time periods before we would classify them as domesticates based on observable genetic alterations (Keeley 1995; Piperno and Pearsall 1998). We reserve the term cultigen for domesticated plants under these same conditions.

A variety of stable subsistence economies, extant, historic, and prehistoric, draw upon elements of hunter-gatherer and agricultural modes of production. These are difficult to characterize in existing terminologies except as "mixed" economies, engaged in what Smith (2001a) has characterized as low-levelfood production. They typically depend significantly on hunting and gathering while to varying degrees using cultigens or keeping domesticated animals. Horticulture, the small-scale planting of domesticated species in house gardens or the use of swidden plots, combined with routine hunting and gathering of wild foods for a significant part of the diet, would be considered a form of low-level food production. Contemporary casual farming by the Mikea hunter-gatherers of Madagascar would be an example of this practice (Tucker 2001; Chapter 2, this volume).

The boundary between low-level food production systems and agriculture is inherently fuzzy. We believe the term agriculture is merited when foraging recedes to an episodic, infrequent or recreational activity, regular provisioning using domesticates takes over daily subsistence, while agricultural work and animal husbandry come to dominate the activity schedules of adults. Although numeric boundaries are somewhat arbitrary and unsatisfactory, agriculture implies that approximately 75% of foodstuffs are acquired from domesticated sources. Although few contemporary societies engage in low-level food production, the archaeological record suggests that mixed foraging and cultivation/husbandry strategies were common and often stable, in the sense that they were practiced by people for thousands of years before they developed a full commitment and reliance upon agriculture (Smith 2001a).

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