Contrariwise, I had some problems with this post at Open Culture, “40,000-Year-Old Symbols Found in Caves Worldwide May Be the Earliest Written Language”:
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.”
The symbols may be communication, they may store knowledge, and there may be commonalities among such inscriptions worldwide but these abstract signs and geometric symbols are emphatically not “written language”.
The commonality and wide distribution can be explained as what’s easy to do using stone implements and commonality in human experience and perception. I know of no evidence indicating that the drawings are representations of spoken language or intended to communicate abstract ideas.
That is, after all, how “language” differs from signing—sounds put together in novel ways and with a grammar to communicate ideas including abstract ideas as opposed to imitating animal calls, sounds, etc. They may be “proto-writing” as old inscriptions in China, Europe, and Africa are sometimes characterized but they aren’t “written language”. That was first developed, probably from one of more of these proto-writing systems, around 6,000 years ago give or take.
There are a couple of different schools of thought on the development of writing. One is that it was invented multiple times in different places possibly including
Sumer
Egypt
China
the Maya glyphs
Another is that it was invented once by the Sumerians (or somebody lost to history from whom the Sumerians learned it) and was widely imitated.
Interestingly, all four of those sources of writing used what are, essentially, rebuses.
There are multiple theories about spoken language for that matter. One theory is that ALL modern languages descend from a common ancestor. Another is that ALL modern languages descend from just three common ancestors (one for inflected languages, one for agglutinating languages, and one for positional languages). Still others think that spoken language was invented many times in many places.