Many, if not most, plants considered decorative flowers originated as weeds, which if attractive enough would sometimes be tolerated by farmers because of their appeal. This led to an artificial selection process, producing ever-prettier (to humans) flowers. This is thought to have occurred for the entire history of agriculture, perhaps even slightly earlier, when people tended to favor naturally occurring food-gathering spots. This may also explain why many flowers function as companion plants to more useful agricultural plants; they had evolved that symbiotic relationship with the food plants before either was domesticated, and therefore was found in the same area, convenient to be selected as an attractive plant.