In some instances he has modified the crop so much that we are not sure what wild organism was the original parent. That is true for Atlantic Giant pumpkins. Even before man, the plants and animals themselves and selection by nature had been practicing genetic improvement. When any animal selects a mate, the future for the species may be slightly different than if a different mate had been selected. It is common to suppose that animal matings in nature occur randomly, but nature photographers have film which show animals work very hard to attract mates.
Many plants have self-sterility factors which force cross pollination.
The cole crops present an interesting demonstration of the power of selective breeding. It is said that most cole crops came from a common origin and that you can begin with any one of these crops and derive any other. The cole crops are cabbage, cauliflower, rutabaga, etc. In the old days, breeders thought the traits of an offspring were due to a blending of the traits of the parents. We now know that blood is not the basis of heredity and Mendel proved inheritance occurs by lumps of genetic matter which we now call genes.