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The climate of South Africa was once much wetter than it is today, and those lush times may have spurred human populations through especially innovative periods, new research shows.

Evidence from these ancient periods suggests humans produced new tools, and used symbolism in wall engravings. The findings suggest a tight link between abrupt climate changes and the emergence of modern human traits, researchers say.

"We provide for the first time really good evidence that the occurrence and disappearance of these first finds of human innovation are linked to climate change," said study author Martin Ziegler, an earth science researcher at Cardiff University in Wales.

Stone tools known as bifacial points recovered from Blombos Cave, South Africa. They were made during the Middle Stone Age, about 75,000 years ago, by anatomically modern humans.