The best theory I have yet heard explain why we are here...
Earth is a penal colony for the rest of the universe. The human look is really just prison garb. When we think about it, it makes sense to me. We humans do treat each other in similar manner to the way inmates threat each other as we hear tales of from within our own prisons.
So, be good and maybe you will get to back to wherever you came from, hoping it is better there than here.
There are certainly a lot of stories passed down through the ages that suggest that possibility.
Tony