You look at something like the following video, of a gorilla, even more distant from us than australopithecus or homo erectus, and even then you see something familiar. Part of it might be human projection, wanting to see something you recognize in another creature. But it is hard to deny that there isn't some emotion going on there, and that she is trying to communicate that emotion using signs...
What would it be like to interact with an even closer early human relative? We will never know, I suppose. That's kind of sad, in a way.
From the YouTube description of the clip:
Koko watches intently a DVD movie on her TV that she has seen several times before. It is called Tea with Mussolini. When it comes to a sad part, where the boy has to say goodbye to all of his relatives and waves goodbye on the train, Koko turns away from the TV. She then proceeds to sign: "Frown, sad, cry, bad, trouble, mother and Koko-love." Her eyes also look very watery. (Gorillas cry too.)
I didn't like that they were taking those flash pictures of her when she turned away from the TV screen.