We also know that groups without writing systems were historically able to adopt writing systems rather quickly, which is, I think, rather good evidence that writing is a technology, not a point of speciation.
Going back to Ancient Greece, Socrates didn't even believe in the effectiveness of writing for communication of knowledge. My poetry professor used to spend some time on this, because it's intimately tied to the art of poetry. He would cite a number of studies showing our emotional responses are intimately tied to our language processing, and that humans are wired to emotionally respond to, and remember, stories.
Even before writing, oral histories were passed down for many generations. For an extreme example, see: https://www.sapiens.org/language/oral-tradition/ .
I won't pretend to know what makes us human, but ultimately I believe it has to be rooted in something neurological, not technological.
Which is why people look into specific elements of language not just huge generalizations.
It fits the basic concept of writing, where complex ideas are communicating through time rather than space.
As to using symbols it depends on what you mean by symbols. Though an ants nest is a dark environment so writing the way we think of it via coloration would be a useless. In such an environment pheromones have inherent advantages, but you can’t get the same highly detailed shapes.