Literacy at its simplest is the ability to decode and encode writing so that symbols on the page or on the screen can be associated with pronounced words in a particular language. Being able to read can precede being able to have a conversation. It can even come before the meanings of some of the words one can read are understood. Little children can do this. Chimpanzees can do this. It is no big deal, and it does not imply a giant leap of intelligence.
I've had people ask me: "Since you say that Bow is literate, does he read books?" My honest answer has always been that I don't think he does. He has been exposed to books since infancy, and he likes to have them read to him, and he also likes to handle them, but so far, I have not seen any evidence that he reads books. He may read a few words here and there, but he does not sit down and sequentially read a book from cover to cover, taking it in the way the author intended.
Bow knows what books are. He has seen me use them in the canonical way, but it's not something he wants to do. So what does he actually do, when given a book to read? Here is a video clip that answers that question.
Notice that Bow holds the book right side up, not upside down. He is interested in getting to know the different parts of the book,and he flips through finding small snippets that are of interest to him, whether pictorial or textual, but his attention span does not allow him to stop for too long on any given thing.
Admittedly, this is a book that is of interest to me because of the subject matter. Bow is not interested in the ideas and personages involved, but I have in the past given him books about other chimpanzees to read, and he treated them about the same way. He would sit for hours -- or at least twenty minute intervals with breaks -- to have me read to him about Nim, but he did not sit for hours reading about Nim himself.
To be honest, I don't read every book sequentially, either. When it's a book that I use for research purposes, I go through the index just like Bow, and I pick up particular passages that have something to do with my own purposes.
Many humans have trouble sitting down and reading a book cover to cover. Bow is not alone in this. If you would like to learn about the problems of other readers, I recommend this blog:
http://thethinkingmother.blogspot.com/2012/12/both-kids-have-eye-reading-problems-now.html
Literacy isn't everything. There are many other components to reading a book besides being able to decode a sequence of letters and make out which word it spells. It isn't magic. And Bow's achievements in literacy do not in any way imply that his intelligence is abnormally high. That claim was never made.
What I am hoping for, someday, is to find a way to prove what Bow really can do. It's not all that remarkable, once you realize what it is, but it would be nice to be able to share this knowledge with others. And maybe if people realized how modest an achievement literacy is for the average human, they might come to be less closed to the idea that a chimpanzee can do it, too.