My uncle did believe in aliens, not so many people did back then so lots of people thought he was a bit odd for it. He thought there must be life on other planets, that in fact we may have had connections to them in some way. I don't think he knew about the belief of many nowadays, of aliens landing on this planet and somehow starting our life form here, either as a direct result of descendants or that they somehow merged their DNA with apes or some or animal here, but if he had he would have jumped on that theory as quite likely, I feel sure.
Personally, I don't know about that, could be true, might not be. But like most people now do believe I think there has to be other intelligent life forms out there somewhere in one of the millions/billions of planets floating around the stars.
What we know, or surmise, about the Universe is all very fascinating and awesome. It's expanding for one thing, growing outwards and spreading apart the distances between the stars. The things we know which are there but can't actually see such as black holes and the immense power they contain is amazing, but also scary when you know they suck up everything around them including whole stars. If they can do that what hope have we to survive?
It's so easy to worry about what is out there, what we don't know about, as well as what we do know. But really the answer is already known, Douglas Adams told us in his book 'The Hitchhikers Guide to the Galaxy'. The answer is 42, yes, number Forty Two. So, now we need not worry anymore. It's the answer to it all, Life, the Universe and Everything - 42. Ah now I feel better for knowing that.