The Makapansgat Cobble

In 1925, teacher Wilfred Eitzman found a cobble—a rock slightly bigger than a pebble, the weight of a small rat—in a cave in Northern Province, South Africa. It was reddish brown with an unmistakable, prominent face etched into it.

Two deep and perfectly round eyes, a shallow divet for a nose, and grimacing, toothy mouth. An outline above the face turns the rounded stone into a head with hair. It looks for all the world like a little carving, but it wasn’t made by any human—it was found...