I am always amused by academics and so called experts that the sheer distance make it impossible for any life form to make it to earth. Distance is only a factor if you need to return to your point of origin, this constant humanization of aliens is a perfect example of human arrogance/racism/specism/primitive proventialism. The visitors are alien not human, they could be insect like or some type or organism that has not been encountered on our planet. They possibly wander outward though out the galaxy, generation after generation born or laid in transit passing their knowledge and discoveries at a genetic level Consider the fact that we now can clone animals and create hybrids in the plant and animal world, how long before we will be able to genetically engineer astronauts that can survive and prosper in zero gravity and with no desire to return home. Imagine being able to transfer knowledge and experience at a genetic level through DNA, isn't this what we are all looking for ...... immortality.