Dr. Ezekiel Zamar reveals his theories
Dr. Zamar states, "The Earth has been visited many times by myriad races. Millions of years ago, our most primitive ape like progenitors were up-lifted by a race we at the Zamarite Institute call the "Prymosians". These Prymosians discovered our proto homo-erectus predecessors, and commenced a process of speeding up their evolution. They up-lifted our ancestors into sentient forms, and spread them to the stars, relocating other branches of humanity further adapted to the environments of planets in star systems both distant and near our own. After working with their human "children" for hundreds of thousands of years, these Prymosians left us to our own devices many thousands of years ago. It seems other aliens have since come into the picture, known in some circles as the "Grays", who now engage in their own genetic projects, further tampering with human evolution. Their motivations look to not be quite as benevolent as the Prymosians."
Unlike Ufologist John Lear, Ezekiel Zamar does not suggest this up-lift creation of humanity precludes the existence of God. Rather he says these Prymosians saw themselves as servants of God, accelerating the natural processes in order to insure greater survival of sentient species throughout the Milky Way Galaxy. So in a sense, Zamar's Prymosians fill the niche of angels, guardians of life from star system to star system.
Zecharia Sitchin's take
Zecharia Sitchin's take on these up-lifters, he calls the Anunnaki, is a bit more cynical, presenting them as imitators of "gods", whose motivation for creating humanity were of a more selfish nature. According to Sitchin, the Anunnaki needed servants to help them with mining gold, and therefore designed humanity for that purpose. Thus by Zecharia Sitchin's reckoning, we were genetically up-lifted to be gold mining slaves.
Examined collectively the evidence can be compelling
Regardless if ones ancient source is Sumerian, Persian, Egyptian, or Israelite all of these were recorded considerably later than the events they have mythologized. Bearing that in mind, it may be much more challenging than these researchers suggest to genuinely comprehend the actual motivations behind the actions of these theoretical extraterrestrial up-lifters. If indeed our ancient ancestors were genetically altered by beings from elsewhere in the universe, the knowledge of why they did so may well be lost to time for us, today. While much may be uncertain, we can be sure of one thing, in spite of a strongly skeptical main line, there is an increasing number of those who do believe the Earth has been visited by extraterrestrial beings. The evidence of these visitation may be slight, and subject to debate, but when examined collectively and with an opened mind it can be quite compelling.