Human
So then, does the world need human observers in order to exist? — Well, quite apart from the fact that indeed we do not know our world without us, this question does not arise actually just because we recognize knowledge in the heart of matter. Rather, in giving a definition of knowledge, we render it independent of subjective notions, it gets an objective appearance. As such we can let it act in the physical, not needing to highlight the subjective human perspective — which we never leave, naturally. In this sense, knowledge is not less objective than any atom or so.
But, of course, objectivity does not remain unaffected by this addition (of knowledge). Ultimately it gets a human component. Which is, maybe, not so bad after all.