It is a deep question, from deep in our history: when did human language as we know it emerge? A new survey of genomic evidence suggests our unique language capacity was present at least 135,000 years ago. Subsequently, language might have entered social use 100,000 years ago.
Great comment always. In addition to dolphins I think it’s possible that corvids might demonstrate certain aspects of grammar too, though I don’t think the research is conclusive yet. I remember reading news about corvids possibly showing capacity for recursion.
Chimps, too. I couldn’t find the article to link here, but I remember seeing somewhere that they have discrete howls that can be combined for subtler meaning; not too far from having a howl for “leopard”, another for “close”, and then using both to say “there’s a leopard nearby”.
The key difference between chimps, corvids and dolphis vs. humans is that humans developed that system to the point it eclipsed non-verbal communication (although we still use it a fair bit).