Few human traits are more variable, more obvious, and more historically divisive than the color of our skin. And yet, for all its social and scientific importance, we know very little about how our genes influence its pigment. What we do know comes almost entirely from studying people of European descent.

To Sarah Tishkoff, a geneticist at the University of Pennsylvania, that’s a ridiculous state of affairs. “It gives you a very incomplete perspective,” she says.

To redress that imbalance, Tishkoff and her team looked to Africa—the continent where humanity is at its most physically and genetically diverse. They recruited 1,570 volunteers from 10 ethnic groups in Ethiopia, Tanzania, and Botswana, and measured the amount of the dark pigment melanin in the skin of their inner arms. Then the team looked at more than 4 million spots in the volunteers’ genomes where DNA can vary by a single letter, to identify which variations are associated with their skin color.