Humans began to rapidly accumulate technological knowledge 600k years ago

The common ancestor of neanderthals and homo sapiens had a larger than normal hole in the skull (the hypoglossal canal) which contains the nerve bundle going to the tongue. They're pretty sure that was the result of language use before 1M BC. There may have been several stages of later improvement after the initial development.

Yet some other evidence places it much later at around 130ky. Go figure.