There are 2 principles of evolution that need to be respected:
Language as a communication mechanism does not easily fit that paradigm. Only relatively advanced mammals like dolphins and lions show social behaviours with division of labour that require communication of the sort that might yield a survival advantage. On the other hand, we assume that many genetically based mechanisms come into play to enable language communication. We therefore assume that it would take very many steps, and therefore very many species, to develop all the enabling neural and other mechanisms to support language as we know it.
It is generally agreed that the initial communication phase for humans was oral, with speech and listening. Writing and reading came very much later, possibly tens or hundreds of millions of years. Unfortunately, not having a written record, it is hard to conjecture on the beginnings of systematic use of oral language for achieving reproductive and survival benefits, or to show steps in its evolution.
There also is no clear fossil or DNA record that identifies and records components of language capability.
In summary, it is difficult to show how the capabilities for oral and written language evolved by looking at typical traces of evolutionary sequences.
We shall propose quite a different approach, based on information processing and an 'inner language' for use within rather than between individuals of a species.