I think about this a lot. I certainly don't believe in Darwinism it just doesn't ring true for me especially with the amount of theories out there that offer an alternative.
I've read hundreds of theories on this subject and I seem happy with the conclusion (for me) that the one that fits is that we came from a much earlier civilization. Atlantis is just one example. Whether its alien or not of course I don't know.
At some point the early civilizations died out or was wiped out. My best bet is that certain elite groups have this knowledge and kept it to themselves and to use to enslave the rest of mankind and empower themselves.
The origin I believe or source of this knowledge is the Middle East or more specifically Egypt. The place (I believe) where the source of religion came from in its many varied forms and the original foundations of modern day economic and social structures.
Anyway the reason for this post is that I found an interesting video which plays into the idea (theory) that aliens are the reason why we have humans on the our planet. Hope you enjoy.