And the most ardent and likely earliest proponent of the"Terrestrial Alien Theory" is the very smart and accomplished Jacques Vallée. His classic work "Passport to Magonia" is a must read and re-read introducing the fascinating connection of Folklore and modern Ufology. YouTube has recent talks he has given. Now in his 80's, he provides an astounding breath of knowledge on many topics with Ufology at its core. His genius is to follow tales of UFO reports track them down and spend all the time needed, even in the remotest parts of the world, to investigate. But his main goal is to interview the witnesses in visceral depth and detail. I admit to being a big devotee of Vallée.
But I have my own pet Theory on the side. The Universe is about 14 Billion years old. Investigations of evolution of The Universe indicate life could have evolved somewhere there in the first 5 billion years. Given that huge 10 billion year head start (life on Earth is 4 billion years old), it is my belief The Universe not only contains life, it is teeming with it. There are multitudes of highly, to super-highly, advanced cultures. WE are visited by many races, cultures, tribes whatever you want to call them.
There may likely be some sort of agreement among these entities on how to handle contact (with lower tribes, us). That would explain the incredible varieties of entities and vehicles seen. Since each group may have its own motivation for interaction with us there could be some animosity or conflict between these groups which could explain some oddities. Physicists today have some pretty deep discussions about this stuff (especially time travel) and can see some support in their research.
You stated: T
hat said, it's interesting how UFOs seemed to grow in sophistication, almost mirroring our progress in air travel. From the airships of the 1890s, flying saucers of the 1950s, all the way up to the triangle ships of today.
The flip side of this is the vintage observer was describing an aerial anomaly with the language of the day.
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