Natural wetlands rather than irrigated fields are the fertile ground from which cities first emerged in Mesopotamia, a scientist doing research in Iraq says.

Wetlands are vital to a sustainable urban environment and the conventional wisdom about irrigation and city-building is backward, said archaeologist and anthropologist Jennifer Pournelle of the University of South Carolina..

"In most people's heads -- archaeologists, ecologists, environmental scientists -- there's the idea that cities happen because somebody invented and managed irrigation," Pournelle said.

"My argument is, 'No -- irrigation is what happened because you had cities but the marshlands were moving away from them,'" she said in a university release Thursday.

"That's what marshes do. Deltas build up, river mouths migrate, and the marshes go with them. The city's stuck where it is, so it has to start irrigating to raise crop production and replace all of the marshland resources that have moved too far away."

Pournelle, who has conducted wetlands investigations in southern Iraq, said more research is needed to establish the relation between natural marshes, irrigation, and the historical beginning and end of city occupation.

"If I can show that this model is durably true, then we need to start paying very serious attention to any city when we start depriving it of its wetlands," Pournelle said. "Things might not be immediately apparent on the scale of 10 to 20 years, but [would be] on a scale of 50, 100, 500, or 1,000 years."