Quite a lot is known about it though.
The hard part is going beyond to the actual roots / development of the "first" language. The origins of speech, as it were.
What I find fascinating about it, is how languages of today actually pretty mirror genetic diversity, as the development of language also follows evolutionary principles.
The "genetic diversity" of a language would then be the amount of different "sounds" each individual language really entails.
The biological "genetic diversity" between a random european and a random asian is smaller then between a random african and his neighbor.
This is due because the group that migrated out of africa back at the dawn of humanity, represents a genetic bottleneck. The "mother population", with thus the most diversity, was left behind in africa. A small-ish group migrated elsewhere.
We see the same pattern in language.
African languages have LOADS more different "sounds" then european or asian languages.
It's very fascinating for sure.