cats

Could be. But that seems more elaborate than “as you’d expect, cat smiles look like human smiles and mean the same thing”

It just means smiling appeared before our common ancestor, or that we co-evolved like bees and flowers to have a working interface for emotional communication.

It’s in all organisms’ best interest to succeed in communicating with other organisms. There’s a universal selective pressure toward universal empathy. Like you can tell when a hornet’s anxious or a spider is scared.

It just so happens we’ve been next to cats for long enough we got highly specialized at reading each other.