I'm pretty sure it's optional and all that, I don't think you'll be really forced to take on a certain pet. I believe there will be different kinds of pets? Correct me if I'm wrong.
I hope you are right. in other games that have one or more pets the most you can do is bring it out somewhere and abandon it.
It would only make sense if it were to be optional because nothing rocks more then having a choice in the say.