The plants that were eaten habitually by hunter-gatherer communities were palatable and non-toxic. These characteristics had been determined by trial and error. Then, by saving the largest seeds from the healthiest plants, a form of selection was practiced that provided the initial foundation of plant domestication and breeding.
Among the fruit and seed characters favored by selection in prehistoric times were cereal stalks that did not fall into separate pieces at maturity, and pods that did not open as they dried out, dispersing seeds onto the ground. Wheat or barley heads that remained unified, and pea or lentil pods that remained closed allowed easier and more efficient collection of grain and seeds.
Science EncyclopediaScience & Philosophy: Planck mass to PositPlant Breeding - Early Selection, Seed Dormancy, Quality, Climatic Adaptation, Pollination And Hybridization, The Impact Of Hybridization On Plant Breeding In The United States