Corn (well, maize) as it exists now was obviously cultivated in specific ways, but I think you'd be hard pressed to actually demonstrate that corn didn't exist in nature prior to that. The fact of the matter is that it makes no sense for early humans to "consciously genetically select" an item for consumption that wasn't consumable beforehand. Now, certainly, I'd be willing to believe that it didn't always exist in nature but became extant there at some point, at which time humans domesticated it and began selecting, with modern corn being the eventual result.

But I guess I'm open to being convinced, if you've got a compelling argument.