We may take it for granted that the earliest writing systems developed with the Sumerians around 3400 B.C.E. The archaeological evidence so far supports the theory. But it may also be possible that the earliest writing systems predate 5000-year-old cuneiform tablets by several thousand years. And what’s more, it may be possible, suggests paleoanthropologist Genevieve von Petzinger, that those prehistoric forms of writing, which include the earliest known hashtag marks, consisted of symbols nearly as universal as emoji.

The study of symbols carved into cave walls all over the world—including penniforms (feather shapes), claviforms (key shapes), and hand stencils—could eventually push us to “abandon the powerful narrative,” writes Frank Jacobs at Big Think, “of history as total darkness until the Sumerians flip the switch.” Though the symbols may never be truly decipherable, their purposes obscured by thousands of years of separation in time, they clearly show humans “undimming the light many millennia earlier.”

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Von Petzinger spent years cataloguing these symbols in Europe, visiting “52 caves,” reports New Scientist’s Alison George, “in France, Span, Italy and Portugal. The symbols she found ranged from dots, lines, triangles, squares and zigzags to more complex forms like ladder shapes, hand stencils, something called a tectiform that looks a bit like a post with a roof, and feather shapes called penniforms.”

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Of course, it’s also possible that both the signs and the animals were meant to convey ideas just as a written language does. So argues MIT linguist Cora Lesure and her co-authors in a paper published in Frontiers in Psychology last year. Cave art might show early humans “converting acoustic sounds into drawings,” notes Sarah Gibbens at National Geographic. Lesure says her research “suggests that the cognitive mechanisms necessary for the development of cave and rock art are likely to be analogous to those employed in the expression of the symbolic thinking required for language.”