Evidence that crop circles are man made.

In the beginning, the circles were quite simple. With time, with practice, they became more complex. In the 80's, with the popularization of fractal geometry, of course, the circle makers exploited it. In the 90's, with the popularization of the computer systems, they exploited the digital designs. You can confirm the trends and evolution of the designs according to the human cultures in any crop circles website.

They seem to be quite simple to make. All what are required are metric tapes, GPS, something that bends the plants and imagination. Also use the truck tracks (those parallel lines seen in the fields like the lines on the pages of a notebook) to not leave footprints.

See the Circlemakers website: [link to www.circlemakers.org] who were once attacked by a group of crop circles believers who hurled heavy stones at them.