After watching another episode on UFO's I started to think why they would visit us here? That's when it hit me. What if, On this planet we are all connected via DNA. Everything is linked so what if the aliens have the same code? They could actually be searching for the ultimate answer, Where does DNA code come from, who or what made it? So being rather more advanced than us they could be out searching for the source of this code when they found this planet and because we had the same/similar DNA Code they decided to take samples to study just as we do here when we look at other species. And because our DNA code is either the same or similar to theirs they started to experiment all to further their search for the source of where does DNA come from?
Like I said, just a thought.