University of Utah anthropologists counted the number of carbon-dated artifacts at archaeological sites and concluded that a population boom and scarce food explain why people in eastern North America domesticated plants for the first time on the continent about 5,000 years ago. "Domesticated plants and animals are part of our everyday lives, so much so that we take them for granted," says Brian Codding, senior author of the study published online August 2 by the British journal Royal Society Open Science. "But they represent a very unique thing in human history. They allowed for large numbers of people to live in one place. That ultimately set the stage for the emergence of civilization."

Graduate student Elic Weitzel, the study's first author, adds: "For most of human history, people lived off wild foods - whatever they could hunt or gather. It's only relatively recently that people made this switch to a very different method of acquiring their food. It's important to understand why that transition happened."

The study dealt not with a full-fledged agricultural economy, but with the earlier step of domestication, when early people in eastern North America first started growing plants they had harvested in the wild, namely, squash, sunflower, marshelder and a chenopod named pitseed goosefoot, a pseudocereal grain closely related to quinoa.

Codding, an assistant professor of anthropology, says at least 11 plant domestication events have been identified in world history, starting with wheat about 11,500 years ago in the Middle East. The eastern North American plant domestication event, which began around 5,000 years ago, was the ninth of those 11 events and came after a population boom 6,900 to 5,200 years ago, he adds.

For many years, two competing theories have sought to explain the cause of plant domestication in eastern North America: First, population growth and resulting food scarcity prompted people to grow foods on which they already foraged. Second, a theory called "niche construction" or "ecosystem engineering" that basically says intentional experimentation and management during times of plenty - and not immediate necessity - led people to manage and manipulate wild plants to increase their food supply.

"We argue that human populations significantly increased prior to plant domestication in eastern North America, suggesting that people are driven to domestication when populations outstrip the supply of wild foods," Weitzel says.