Scientists at the Primate Research Center in Kyoto have watched generations of macaques pass stone-handling techniques from mother to child, said Michael A. Huffman, a primatologist at the center.

In their study, stone-handling included rubbing and clacking stones together, hitting them onto hard surfaces, picking them up, and cuddling, carrying, pushing, rolling and tossing stones.

The scientists found the stone-handling behavior changed with each generation as individual monkeys contributed their own patterns of stone-handling.

"Research on such transformation may shed light on the evolution of stone-tool use in early hominids," Huffman said.