Humans began to rapidly accumulate technological knowledge 600k years ago

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?

We think in something Steven Pinker termed “mentalese”. It is distinct from human language. There are many examples of people who are cognitively normal, but either lack or have severely impaired language for various reasons.

The distinction between reason and language is not widely appreciated, and is a main if not the primary reason people overestimate the abilities of LLMs.