Topic: The Panspermia theroy and why it may be right.
Panspermia theory states that very simple life may have been planted on planets (Earth or otherwise) via comets or meteorites. If a planet has suitable compounds, it may take the life and the evolutionary cycle starts. If Reptilians, Greys, or others are real, and they are as humanoid as they are pictured, it is likely that we are brothers from some far off father. Is the human form (Two eyes, two legs, two arms, one head, etc.) that ideal that it would be so common without us having a common ancestor? This is just a suggestion, to be taken or left.
I would imagine that most sentient extraterrestrials able to travel intergalacticly of their own free will would share more in common with computers than humans. A large chunk of almost pure computational matter would seem quite a bit more likely of a candidate to make it far enough to interact with us than a humanoid shaped reptile unless Panspermia is true. Thus, if the aliens are as people claim, Panspermia is likely the cause of our similarities. This Panspermia could've been caused by rare chances in nature, or it could've been done by a race that sought to propagate (for whatever reason).