Agriculture is based on domestic plant engineered by early farmers from their wild plant ancestor. Without perhaps much of an awareness of what they were doing, early farmers selected plants with desired characteristics for the production of food. This selection of plant for domestic use brought about evolutionary change so profound that the products often barely resembled their wild ancestors. Plant breeding based on scientific principle of heredity is a very recent development dating from around 1900. One of the major objectives of plant breeding has been to increase yield. Yields of crops can also be increase nutritional value, such as raising the content of essential amino acids.