Final answer:
The oldest crop believed to be propagated by grafting is wheat, first cultivated in the Fertile Crescent about 10,000 years ago. This crop was instrumental in the development of ancient civilizations and was genetically modified through the ancient practice of selecting and planting seeds with desirable traits.
Step-by-step explanation:
The oldest crop believed to be propagated by grafting is wheat. This ancient grain was first cultivated in what is now Turkey about 10,000 years ago, even though some researchers suggest it could be older. Originating in the Fertile Crescent, a region stretching from the Persian Gulf to the eastern Mediterranean, wheat's propagation played a crucial role in the rise of civilizations like Egypt and Mesopotamia between 6,000 and 5,000 years ago. The process of selecting and planting seeds from plants with desirable traits, such as large seeds, drove the genetic modification of crops, a process Darwin referred to as 'artificial selection'. Wheat, through primitive agricultural selection for plants with favorable traits, became a staple crop and one of the first to be propagated by humans.
While agriculture developed in multiple regions around the world including the Middle East, northern China, and Mesoamerica, each spot is known for the domestication of key staple crops. In addition to wheat, humans domesticated other crops such as barley, peas, lentils, carrots, olives, dates, rice, millet, soybeans, sorghum, maize (corn), beans, squash, peppers, and potatoes. These crops were originally wild plants that humans discovered to have desirable features which were then cultivated and selectively bred for improved yield.
It is remarkable that only about fifteen staple crops account for 90% of the calories consumed daily worldwide. With maize topping the list, developed from teosinte in central Mexico, and followed by rice, wheat, potatoes, and cassava, these crops have shaped human history and the development of civilizations through the ages.