By Bruce Bower, Science News
It apparently took a long time to get the Agricultural Revolution off the ground. Prehistoric hunter-gatherers in the Middle East cultivated the farming life over more than a millennium, largely thanks to their proficiency at building structures to store wild cereals, a new report suggests.
Excavations at Dhra' near the Dead Sea in Jordan have uncovered remnants of four sophisticated granaries built between 11,300 and 11,175 years ago, about a millennium before domesticated plants were known to have been cultivated there, say archaeologists Ian Kuijt of the University of Notre Dame and Bill Finlayson of the Council for British Research in the Levant in Amman, Jordan.
Microscopic pieces of silica from barley husks were identified in one structure. Though intact cereal grains have yet to be found, the granaries were situated between oval-shaped buildings where the researchers found stone tools for grinding wild plants.
Discoveries at Dhra' represent the oldest known evidence for systematic storage of wild grains, the researchers report in an upcoming Proceedings of the National Academy of Sciences.
A nearby site dating to at least 12,800 years ago contains pits that may have held wild plants, but no food remains have been found there.
Ancient residents of Dhra' and several nearby settlements sowed wild cereals in fields and stored surplus food in granaries, making it possible to establish permanent communities before farming of domesticated plants began, Kuijt and Finlayson propose.
“The most important implication of our findings is that fundamental social changes occurred before plant domestication, including the establishment of fairly permanent settlements, with communal labor and storage, based on cultivated wild plants,” Kuijt says.
Researchers now generally accept that people in the Middle East and Asia must have cultivated wild plants for between 1,000 and 2,000 years, with annual harvests in the fall, before domesticated species appeared, remarks Harvard University archaeologist Ofer Bar-Yosef.
“The discovery in Dhra' provides us with one of the earliest well-built examples” of a food-storage structure from before plants were domesticated, Bar-Yosef says.
Storage structures there support the argument that the sowing of wild plants beginning as early as 14,000 to 15,000 years ago led to agriculture, comments archaeologist Mordechai Kislev of Bar-Ilan University in Ramat-Gan, Israel.
One especially well-preserved granary reveals a sophisticated design. Upright, notched stones inside the circular structure held horizontal wooden beams for a suspended floor that provided air circulation and protected food from rodents, Kuijt suggests.
A second granary was built on top of the first one, according to the researchers. Radiocarbon measurements from charred wood indicate that each structure was used to store wild plants for no more than 50 years, the first beginning around 11,300 years ago and the second starting shortly after abandonment of the first.
Investigators of other Middle Eastern sites from the same time have hypothesized that “pioneer crops” of cultivated wild cereals, including barley, lentil and oats, were eventually domesticated.