Who swung the first hammer stone? Early human ancestors may have hefted tools more than three million years ago, ancient hand bones suggest. That’s roughly half a million years earlier than the oldest stone tools yet discovered.

The hand-bone analysis, led by the United Kingdom’s Matthew Skinner of the University of Kent in Canterbury, compared the internal structure of hand bones from modern people, chimps, apes, Neanderthals, and early human species.

Most notably in the study, released Thursday by the journal Science, researchers report on the hands of Australopithecus africanus, best known from the pierced skull of the famed “Taung child,” who may have been killed by an eagle about 2.5 million years ago.

While the pattern of spongy bone