Open Question to David Peterson

In this video, which is overall a pretty good one, this language inventor, this colleague in one of the trades of Tolkien, is saying "language is literally the greatest invention in the history of mankind" ... watch all of it before reading my question back to him:

Why language is humanity's greatest invention - David Peterson #shorts #tedx
12th Sept. 2022 | TEDx Talks
https://www.youtube.com/watch?v=B8mHUYdMmZQ

David Peterson, all respect for your creation of Dothraki, more fleshed out than Quenya, I gather, and High Vallyrian and a few more, and "a few" is perhaps understating it, but it so happens, all the languages you have invented are to yourself second languages. Languages you acquire as an adult.

Could you have invented a native language for yourself if your parents hadn't had one?/HGL

(A little hint : the wikipage Origin of language and the a linea Lexical-phonological principle show both (this a linea) the challenge to be met and (other subsections) the wild guessing about how it could be met as to how man is supposed to have invented language.)