And how do you conclude that early humans did not have spoken language ?
There are no recordings to prove it.
Seriously, the stuff I have read suggests the big brain influence was tool use, and language skills came later.
What I point out is if indeed sophisticated languages (other than basic point and grunt) developed after the big homo sapiens sapiens brain was already there, and that same big brain could develop the theory of relativity or figure out how to transplant a heart and lungs, what mutation triggered the big brain and sustained the big brain? We know a mind is a terrible thing to waste, but a big brain in 98,000 B.C. would have been a waste. Sure fire was big, but rocket science was not.
Compress time, it doesn't matter. We are still the same biological beings as the cavemen of 100,000 years ago. The fact is today I could pull a baby from the dregs of the third world, and put it through the best education system available, and probably produce an above average modern first world adult. By the same token, I could take H.G. Wells time machine, go back 100,000 years, pull a baby out of a cave, bring it to the 21st century, and do the same.
What put a brain capable of a million times more cognitive capability on the planet 100,000 years early?
It is a mystery. But one I have not heard before. How did the human brain make such a leap?