An unexpected discovery by an Iowa State University researcher suggests that the first humans may have arrived in North America more than 30,000 years ago – nearly 20,000 years earlier than originally thought. Andrew Somerville, an assistant professor of anthropology in world languages and cultures, says he and his colleagues made the discovery while studying the origins of agriculture in the Tehuacan Valley in Mexico. As part of that work, they wanted to establish a date for the earliest human occupation of the Coxcatlan Cave in the valley, so they obtained radiocarbon dates for several rabbit and deer bones that...