"A sizeable number believe that we were created by space aliens 40,000 years ago."
A theory which I do not hold to (due to our DNA simlarities with other life here), but I am not willing to say it is impossible that dna of existing species on Earth was not altered at some time or other, possibly by aliens. It is, so far, unprovable either way. But is an interesting idea which deserves some exploration, IMO.
Yeah, it is unprovable unless some surprising things turn up. Don't know what practical difference it would make anyway.