WASHINGTON (AP) — Early human ancestors during the Old Stone Age were more picky about the rocks they used for making tools than previously known, according to research published Friday.

Not only did these early people make tools, they had a mental picture of where suitable raw materials were located and planned ahead to use them, traveling long distances.

By around 2.6 million years ago, early humans had developed a method of pounding rocks together to chip off sharp flakes that could be used as blades for butchering meat.

This allowed them to feast on large animals like hippos that gathered near a freshwater spring at the Nyayanga archaeological site in Kenya.

“But hippo skin is really tough” — and not all rocks were suitable for creating blades sharp enough to pierce hippo skin, sai

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