Language and Thought

When you think, how do you think?  For me, it feels like I am having a conversation with myself.  Which came first in each of us, though?  Language or thought?  It’s really a fascinating question, when you stop and think about it.  Are language and thought inextricably intertwined?  If you didn’t have language, could you think the thoughts you think?  Or is our higher-level thinking only possible because of our faculty with language?  It seems like more and more that the answer is the latter rather than the former.