The quality of fruits and nuts varies from plant to plant, not just from species to species. Most food crops do not produce consistently when reproduced by seed. Apple trees always produce apples, but good apples are rare. Preserving individual trees and plants by grafting their living tissue to genetically similar plants began early in human history and remains a mainstay technique of modern agriculture.
Indo-European agriculture began in the Middle East about 12,000 years ago with the domestication of wild grain. Annual grasses evolved physical characteristics which enhanced their relationship with early farmers. Large, strong seed heads survived harvest by humans more often than small, brittle ones. Human intervention naturally selected the plants with the best agricultural adaptation. Long-lived woody plants like fruit and nut trees react too slowly for this quick domestication. As early as 1000 B.C., farmers developed a way around that problem---cloning select individual plants by grafting.
Exactly how grafting developed isn't known. One theory, promoted by authors Barry Juniper and David Mabberley in "The History of Apples," suggests that occupants of shelters with frameworks of living saplings played a part. Bending and tying the tops of young trees together for the supports of a hut could fuse the trees together. In natural conditions where trees of the same species cross limbs, this same conjoining occurs. Inspired by this, early orchardists may have experimented first with lashing limbs to limbs in fruit tree thickets and then developed better methods.
Sumerian clay tablet fragments mention the transport of grapevine cuttings for replanting, but do not specifically describe any grafting method. Biblical agricultural references do not include descriptions of grafting. One Talmudic passage authored in 300 A.D. mentions grafting species to different species as forbidden by law, implying that the method existed in biblical times. The first clear references to the art come from Greek and Roman sources in 500 A.D. and speak of grafting as an established practice.
Grafting in its early days drew some official criticism as a potential mixing of species forbidden by religious law. Prejudice against grafting continued even into early American history. Though famed for spreading the apple tree through early America, Johnny "Appleseed" Chapman spoke of grafting as an injury to the tree. Interspecies grafting became one of the most important applications, introducing disease resistance to threatened crops. Grafting French wine grapes to American rootstocks at the close of the 19th century saved that entire industry from destruction by blight.
Though grafting introduces new dangers by spreading vulnerable individual genetics, benefits outweigh risks. Grafting creates new industries from scattered wild individual plants. A modern example, the pecan tree, served as an important food source for Native Americans. In the mid-1880s, efficient pecan grafting techniques transformed a chance wild harvest into a commercially important crop.