The transition to agriculture in northwestern China

Agriculture can evolve independently only where intensive hunter-gatherer plant use has previously evolved, and both developments are limited by two major evolutionary constraints: climatic variability and social convention. During the Pleistocene, environmental variability constrained plant productivity and therefore plant-intensive subsistence; but during the Holocene it was the hunter-gatherer social conventions that constrained the evolution of plant-based agricultural subsistence. Specifically, in places with continuous hunter-gatherer occupation (i.e., the Near East), social conventions prohibiting the ownership of land curtailed intensification and prolonged the transition to agriculture. In contrast, northwest China was virtually uninhabited during the Early Holocene. Here, new social orders favoring the ownership of land were free to emerge without restriction, so the transition to agriculture was rapid. Semi-permanent settlements and domesticated broomcorn millet emerged abruptly in the western Loess Plateau at Dadiwan by 7.0 ka with no local hunter-gatherer ancestry. We propose that the intensive plant specialization required for domestication and incipient agriculture emerged first in the desert margins north of the Yellow River and migrated southwards to the more humid and fertile floodplains of the Loess Plateau west of the Liu Pan Mountains, perhaps in response to increasing aridity and climatic instability during the Early Holocene.