[The Duke]

Who is to say that these "aliens" are not actually another indigenous species ... who simply moved as far out of the neighborhood as they could when "modern" man came along?

[Keith]

Frankly, Duke, my present theory involves the concept that we are someone elses garden, and that many of these visitors are checking in from time to time to see how things are going. The reason this phenomenon started in earnest in 1947 when the sighting that coined the term "flying sauces" happened at that time was that it was shortly after we exploded our first nuclear device. I think that made several interested parties sit up and take notice.