There is the Sumerian Creation Theory. It firmly states that we were Bio-engineered by a race of aliens using their own DNA coupled with a humanoid creature from Earths DNA. They then fertilized an egg and implanted it into one of their own females who in turn gave birth to the first Human, who at that point, was sterile. It was later on that they decided to let Man begin to create their own young. According to the Sumerians we were created as a workforce in the beginning....but why would they have left as to our own devices in the end??