Humans first took the leap from village life to urban sprawl in Mesopotamia sometime during the 4th millennium B.C.E. in what archaeologists call the Uruk phase, named after a southern Iraq metropolis. But recent excavations in Kuwait, Syria, Iran, and Saudi Arabia provide mounting evidence that the origin of the urban revolution is to be found in the prior era, called the Ubaid, which lasted from 5500 B.C.E. until about 4000 B.C.E. Some archaeologists argue that crop irrigation and the resulting food surplus spurred the rise of cities, while others cite the appearance of kings, colonial domination, or spread of a common religion. But the new Ubaid finds add weight to the hypothesis that growing contact among different groups was the spark that eventually ignited the urban revolution, suggesting that the Ubaid was a time of mutual exchange among independent peoples rather than control asserted by a single sophisticated group.Unfortunately, the full article is behind a pay wall.