6. Domestication rates in wild-type wheats and barley under primitive cultivation

Abstract

Man's first cereal crops were sown from seed gathered from wild stands, and it was in the course of cultivation that domestication occurred. This paper prcsents thr preliminary rrsults of an experimcntal approach to thc measurement of domestication rate in crops of wild-type einkorn wheat exposed to primitive systems of husbandry. The results indicate that in wild-type crops of einkorn, emmer and barley (a) domestication will have occurred only if they were harvested in a partially ripe (or near-ripe) state using specific harvesting methods; (b) exposure to shifting cultivation may also have been required in somr cases; and (c) given these requirements, the crops could have become completely domcsticatrd within two centuries, and maybr in as littlr as 20-30 years This paper ( I ) considers the possible lrngth of delays in the start of domestication due to early crops of wild-type cereals lacking domestic-type mutants; (2) examines the combination of primitive husbandry practices that would have been necessary for any selective advantage to have been unconsciously conferred on these mutants; ( 3 ) considers the state of ripeness (at harvest) necessary for crops to be able to respond to these selective prcssures; (4) outlines field measurements of the selective intensities (selection coefficients) which arise when analogous husbandry practices are applied experimentally to living wild-type crops; (5) summarizes the essential features of a mathrmatical model which inrorporatcs thcsr mcasurrments of selection coefficients and other key variables, and which describes the rate of inrreasc in domestic-type mutants that would h a w occurred in early populations of wild-type cereals under specific combinations of primitivc husbandry practices; ( 6 ) considers why very early cultivators should have used that combination of husbandry methods which, we suggest, unconsciously brought about the domestication of wild wheats and barley; and (7) concludes by considering whether these events arc likely to havc left recognizable tracrs in archaeological remains.

Integrating the processes in the evolutionary system of domestication

“…1a) in which Hillman and Davies (1990) demonstrated by using sickle based harvesting proto farmers could have fixed the tough rachis trait within a human generation, 20 years or so. In their model the proportion of mutant phenotypes was enriched in the harvested fraction, where harvesting took place at a point half-way through the natural grain shedding stage in the cereal's lifecycle, and most of the (wild type) grains that were shed to the ground were naturally predated.…”

“…To consider the strength of artificial selection we can return to the classic work of Hillman and Davies (1990) in Fig. 1.…”

Molecular Diversity, Structure and Domestication of Grasses

“…Large quantities of grass (and grain) are required before they are useful. For example, if 10 people derived 10 % of the calories from wild Triticum or Zea, they would have to grow roughly 1-6 ha of plants (Hillman and Davies, 1990). Roughly 250,000-350,000 plants would have to be grown annually.…”

The genetic expectations of a protracted model for the origins of domesticated crops

“…This corollary appeared to be reasonable based on the rapid appearance of crops in the archaeological record, classic field experiments that demonstrated the possibility of domestication in 20 years or so (6), and the notion that cereals could not have survived in the Near East until after the dry conditions of the Younger Dryas (7). The rapid-transition model supported the notion of the Neolithic Package (8), which implied that the various different crops were brought into domestication by the same group of early farmers.…”