When I remember crop circles for the first time, the patterns were very basic and gave to the idea (from the media mostly) that the spacecraft made the crop circles by actually landing on the ground thus causing the depression and shape. That was probably 20 or so years ago, and as time goes by the CC have got considerably more elaborate and complex.
I was thinking the same thing -- the complexity of the patterns seems to parallel the advances in computer technology. From simple circle patterns to ASCII text in binary along with a nicely shaded picture of a gray in a couple of decades? I'm talking about the one from 15 Aug 2002, Hampshire UK, CCDB ref id: uk2002dl -- "[....] conduit closing (BELL SOUND)" -- Bell sound? You mean ctrl-G?
Consider also that computers have gotten much better at controlling industrial robots, autonomous vehicles, etc.
I think this is a human phenomenon but I find it hard to believe that it's just a bunch of people with wood planks, stepping on plants -- just consider the type of damage on the crops, the sudden appearances, etc. I suspect this is some exotic technology at work, used by humans, controlled by human made computers. I'm not ruling out pranks but it could also be some people on the "inside", sending messages to the rest of us. Or maybe it's just misdirection, to distract us from other things. But I think human beings are behind this phenomenon. IMHO of course!




