Lee Berger is standing in a death trap, smiling. It is a hole in the ground about 25 miles northwest of Johannesburg, in a ridged brown valley where herds of giraffes occasionally parade between stands of trees. The red-rock walls of the pit are higher than Berger's head, and steep enough in spots to make a scramble up, or down, rather daunting. Some two million years ago, the hole was a great deal deeper, with no possibility of escape for any creature that fell in. This accounts for the trove of fossils Berger is finding, which in turn accounts for his upbeat mood. He leans over a red boulder near the pit bottom, tracing a white-colored protrusion with his fingers. "It looks like part of an arm," he says. "That means we've found another individual."