The domestication of plants required years, if not centuries, of trial and error. What is Diamond's evidence of this?from ch.7 of Guns, Germs, and Steel by Jared Diamond
Jared Diamond gives a number of different bits of evidence for the idea that plant domestication took a long time.
One piece of evidence comes from corn. He points out that the oldest corn cobs we know of are about half an inch long. By 1500 AD Mexican Indians had cobs about 6 inches long. Modern cobs can be up to 18 inches long.
Diamond also mentions almonds. He says that wild almonds are already found in archaeological sites from 8000 BC. Domesticated almonds are not found until 3000 BC.
These are the two bits of evidence that most easily show your point.
While the total domestication process involving domestication of different types of plants and development of new varieties of plants from the older ones, did continue for a very long time and developed independently, according to Diamond, domestication of each and every variety of plant did not take that long. As a matter of fact Diamond has stated in Chapter 7 of Guns, Germs and Steel that "conversion of wild to domestic crops seems to have begun when seeds were accidentally sown in latrines and garbage middens". This type kind of domestication did not really require much time. However as the practice of farming led to people following more settled life, they could experiment with experiment with domestication and improvement of different types of plans, which did take a very long time. As a matter of fact this process of improvement is still continuing in forms of agricultural research and development of genetically modified plants and agricultural products.