Double Cropping the Earliest Agriculture

Bountiful harvest.
Barley may have been domesticated more
than once.

Doug Wilson / USDA

A new study suggests that barley may have undergone domestication twice, a finding with important implications for understanding the spread of farming.

Archaeologists have long debated whether the so-called founder crops of the agricultural revolution--including wheat and barley--were domesticated once or multiple times. The record is ambiguous. Over the past decades, they have unearthed the earliest remains of domesticated barley at sites in the Fertile Crescent that date back 10,500 years. But there is also evidence for barley cultivation about 9000 years ago at sites further east in Central Asia. Today, the wild progenitors of domesticated wheat and other founder crops grow only in the Fertile Crescent, but wild barley is found in the western and eastern regions. As a result, archaeologists haven't been sure whether the cultivated barley in the east came from the Fertile Crescent or was domesticated directly from local wild plants.

To find out, evolutionary biologists Peter Morrell and Michael Clegg of the University of California, Irvine, sequenced genes of wild and domesticated barley from the two regions. They focused on seven genes that differ slightly according to the plants' geographic origins. The genetic variations in the eastern domesticated samples much more closely resembled those in the wild plants from the east than those in wild plants from the Fertile Crescent, they report online this week in the Proceedings of the National Academy of Sciences. Morrell and Clegg conclude that barley was domesticated at least twice, first in the Fertile Crescent and then between 1500 to 3000 kilometers further east in Central Asia.

Archaeobotanist George Willcox of the National Center for Scientific Research in Lyons, France, says that the paper demonstrates that the origins of agriculture "are far more complex than the simplistic view of a single event." Willcox adds that there might have been more than two domestications of barley and other crops, but that the evidence for them has been lost: "Archaeology tells us that sites were abandoned, cultures came to a dead end, and with them their crops."

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