UFOs have anything to do with crop circles?

After more than a decade of close observation, there is still no concrete evidence that crop circles are related to UFO sightings. The crop circle phenomenon has many intriguing facets that many people would like to attribute to nonhuman intelligence --including discoveries of cellular changes in the plants, possible radiation fluctuations in soil samples, and unusual geometric relationships.

These effects are exciting, but they do not constitute proof of UFO activity. Nor do they constitute proof that crop circles themselves are mysterious.

Current theories on what causes the circles include unusual whirlwinds, electromagnetic fields, microwave energy, earth energies connected with Stonehenge, and hoaxes.

And it is certainly true that the great majority of circles are done by hoaxers, who have become more sophisticated over time.