Consider for a moment this page from a very old book:
It was written roughly 1000 years ago. It's written in English, but the language has changed so much since then that it is hardly even identifiable, much less actually readable, by modern English speakers/readers (excepting those who've specifically studied old English, of course). It has changed so much that Old English and Modern English should really be thought of as separate, distinct, languages, much like comparing modern English to French or German, for example.
Now consider this question:
Who was the first speaker of modern English?
It's sort of a silly question, isn't it? Was there some individual person who just started speaking an entirely different language from the one her parents taught her, a language that no one around her could speak or understand? No. Of course not. That's not how languages evolve.
That's also not how species evolve. In both cases, it happens by an accumulation of small changes, such that no generation is incompatible with its immediate ancestors or descendents. So, just as there was no very first speaker of Modern English, there was no very first human.