You have to think that there were breakthroughs in communication technology — not just language in general but possibly also one individual who happened to be good at explaining things, either before or after language, who both taught more people, but also taught them how to teach — that led to step changes in technology.
Theory: there are no humans without language. Consider: what language do you think in?
"inner monologue" exists whenever people have hopes, dreams, plans, etc--thats what humans being intentional agents mean. Sure, there is a spectrum: those whose monologue is so active during the wakeful time to those whose daily brief monologue is about what to say in tomorrow's scrum standup.