The first pueblos appeared at Mesa Verde sometime after 650; by 850 more than half of Pueblonians lived in them. As local populations grew, Puebloans found it difficult to survive on hunting, foraging, and gardening, which made them increasingly reliant on domesticated corn. This shift from semi-nomadism to a "sedentary and communal way of life changed ancestral Pueblo society forever". Within a generation the average number of households in these settlements grew from 1-3 to 15-20, with average populations of two hundred people. Population density increased dramatically, with as many as a dozen families occupying roughly the same space that had formerly housed two. This brought increased security against raids and encouraged greater cooperation amongst residents. It also facilitated trade and intermarriage between clans, and by the late 8th century, as Mesa Verde's population was being augmented by settlers from the south, four distinct cultural groups occupied the same villages.
