I don't know exactly what to believe. I know my daughter, and I saw something which we couldn't explain. My mind is open.
I have heard a theory from John Lear, his father was the designer of the Lear Jet. John, himself, was a very accomplished pilot and a sceptic until he had a visit from an old friend who was at RAF Bentwaters for the Rendlesham Forest Incident.
In any case, Lear posits the theory that humans are essentially an "experiment" and something of a hybrid developed by another civilization. Which is why our scientists struggle to find "the missing link," here on Earth.
They, come back to check on, and monitor their creation and do some experiments, which may explain some abductees claim of medical experimentation, and their fascination with emotions (the Greys supposedly aren't capable of them) and human reproductive parts.