Can you name animals in iPhotos?

Not really. You can do it individually on a photo by photo basis like I did here:

But Photos doesn't find other photos of the same animal (or relative). Only those that I manually identify are included in the People section of the library.

That's not an animal, it's Uncle Clyde!🤭

I brought up the Info pane for the photo and selected the Add Face and named it. But the only photos of Clyde that get in the People section are those I manually identify myself.