Or known is the USA as "Five Million Years to Earth", had this plot although a little more "out there" -- but it essentially claimed that we were all descended from Martians. They came here in a spaceship and integrated their DNA into the indigenous life-forms and presto, that's where we came from.
BTW: If you've never seen this film, it scared the crap out of me as a kid. I didn't sleep for a week. It still sends chills down my spine.