I've heard this theory before. I don't believe I have quite made up my mind as to the validity of it. You see, there is no evidence to prove anything. I do believe there are aliens. Though the physical evidence does not support this belief, at least in scientific terms. But there certainly is enough eye witness accounts to convince me that all these people can't be wrong. Perhaps we are an experiment and the reason for the increased sightings since 1947 is because the experiment is going terribly wrong. 

Another theory I have heard; which I find very interesting, is that the aliens that visit this planet are us from the future. Having mastered the capabilities of time travel they are attempting to bridge the gap from their time period to ours in order to warn us of the wrong turns taken in history (their history our future) because that is the only way to save themselves - if they have us change their past. 

I find both concepts intriguing but unfortunately without proof it is difficult to say which is true and which is not. I am, however, inclined to believe that our society has been influenced by alien life forms throughout our history. Whether that influence is the result of breeding experiments or in some other manner is the question. 

When one looks at the world, the advancements throughout history, it seems that in the first few thousand years we did not advance technologically much. But in the last sixty years the advancement in technology has out done itself. This, in my opinion, is evidence of alien influence. When you look at the time-line from 1947 to present day there has been a huge amount of technological advancement...from the mainframe computer to the personal computer...from radar enhancements to the ability to fly in stealth mode...from land-lines to cellular phones...it seems to me that man, in the last 50 to 60 years, had a sudden surge of knowledge. The question one must ask is this the results of back-engineering or were we just lucky to have enough highly intelligent beings on our planet in these last 50-60 years?