MADRID, SPAIN—It had been previously thought that the practice of herding domesticated animals may have spread across Africa through exchange networks, but Science News reports that a new genetic study of human remains unearthed in East Africa tells a different story. The researchers found that early herders, who were related to Middle Eastern pastoralists, first mixed with foragers in northeast Africa between 6,000 and 5,000 years ago. They then traveled south to the Rift Valley, where they mated with foragers there between 4,500 and 3,500 years ago. Mary Prendergast of Saint Louis University and her colleagues say that after this time, herders and foragers living in East Africa remained isolated from each other, although the herders spread rapidly throughout the region. Then, some 1,200 years ago, the study suggests that additional groups of people from northeastern and western Africa migrated into East Africa, where they produced another genetic shift that paralleled the rise of farming and ironworking. For more on hunter-gatherers in Africa, go to “First Use of Poison.”