 Crop circles have been described as all falling "within the range of the sort of thing done in hoaxes" by Taner Edis, professor of physics at Truman State University.Although obscure natural causes or alien origins of crop circles are suggested by fringe theorists, there is no scientific evidence for such explanations, and all crop circles are consistent with human causation.The number of crop circles has substantially increased from the 1970s to current times.