ScienceWeek

ANTHROPOLOGY: ON AUTONOMOUS CULTIVATION BEFORE DOMESTICATION

The following points are made by E. Weiss et al (Science 2006 312:1608):

1) It is widely believed that the primary domesticated crops of the Neolithic -- namely, einkorn wheat, emmer wheat, barley, lentil, pea, chick pea, and flax -- appeared initially in a core area from which they spread throughout the Middle East (1,2). Recent archaeobotanical data, however, indicate that predomestication cultivation of some of these species was carried out autonomously in very early sites of the Near Eastern PPNA (Pre-Pottery Neolithic A; ~11,500 to 10,300 calendar years before present). Moreover, the data also suggest that some of these crops did not develop into fully domesticated species because their cultivation was abandoned by the local populations.

2) Human domestication of plants can be divided into three stages: "gathering", in which people gathered annual plants from wild stands; "cultivation", in which wild plant genotypes were systematically sown in fields of choice; and "domestication", in which mutant plants with desirable characteristics were raised. Cultivation is the essential stage, as the repetitive cycle of sowing, collecting, and sowing of wild plants gives rise to genotype accumulation that leads to domestication. Given the prevailing view that human selection of domesticated plants was not carried out intentionally, agro-evolution would have to take place over hundreds of years (3). The novel characteristics distinguishing domesticated from wild plants are by necessity species-specific. In the Neolithic primary domesticates, these include nonarticulating ears and plump grains in the cereals, pods that do not spontaneously release their seeds (indehiscence), and nondormant seeds in the pulses (i. e., peas, beans, lentils, and other legumes).

3) Archaeobotanical evidence indicates that different Near Eastern communities throughout prehistory cultivated various local species. Some of these early communities abandoned their plants, which represents a local dead end on the road to domestication. Thus, the initiation of agriculture in one place does not imply that the successfully grown plants would be continuously cultivated, an idea commonly recorded in the literature (1). Consequently, the location of the germ plasm of wild-plant founder stocks genetically associated with a particular fully domesticated plant (1) are, in reality, just the stocks that led ultimately to the domesticated plant. There might indeed have been earlier predomestication efforts--with different wild stocks -- that were abandoned by the ancient society.

4) Two criteria identify cultivation in PPNA archaeobotanical assemblages. The first is the presence of a conspicuous quantity of seeds in greater amounts than would have been yielded by harvesting local natural stands of the wild plant (4). If such an amount exceeds the yield of local wild stands, it eliminates the possibility that the local human community gathered it in the wild. The other criterion is the presence of predomesticated seeds that are mixed with plant seeds that grow as weeds in contemporary fields (5). This link could only have been established after humans started to manage fields, allowing weed plants to adapt to human-induced environmental conditions. Therefore, their coexistence indicates sowing rather than collecting of wild stands.

References (abridged):

1. F. Salamini, H. Özkan, A. Brandolini, R. Schäfer-Pregl, W. Martin, Nat. Rev. Genet. 3, 429 (2002)

2. D. Zohary, M. Hopf, Domestication of Plants in the Old World (Oxford Science, Oxford, ed. 3, 2000)

3. M. Kislev, Isr. J. Bot. 50, S85 (2002)

4. Y. Garfinkel, M. Kislev, D. Zohary, Isr. J. Bot. 37, 49 (1988)

5. W. van Zeist, J. A. H. Bakker-Heeres, Palaeohistoria 26, 151 (1984)

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