The genus Arachis L. probably originated as a geocarpic form of Stylosanthes Sw. on the old Brazilian Shield in what is now southwestern Mato Grosso do Sul, Brazil or northeastern Paraguay. Several mid-Tertiary uplifts followed, raising the penaplain and the ancient Arachis with it. The two most ancient species are still found in the area today, comprising the taxonomic section Trierectoides Krapov. and W.C. Gregory. From this beginning the other species and sections evolved as the shield was uplifted and eroded by the tributaries. The more advanced species, but still quite ancient, are in sections Extranervosae Krapov. and W.C. Gregory, Triseminatae Krapov. and W.C. Gregory, Heteranthae Krapov. and W.C. Gregory, and Erectoides Krapov. and W.C. Gregory. The evolution and distribution of these species was a slow process because of the geocarpic fruit, which would have limited movement to an estimated 1 m/yr. However, after several geologic uplifts, flowing water likely played a large part in the distribution of the Arachis species. From the early materials evolved the more advanced species in sections Caulorrhizae Krapov. and W.C. Gregory, Procumbentes Krapov. and W.C. Gregory, and Rhizomatosae Krapov. and W.C. Gregory. The evolution of species in the most advanced section Arachis, which includes the cultivated peanut, has overlapped the distribution of other sections, and the distribution of some members of section Arachis has been strongly affected by man. There is evidence that development of the major domesticated species, A. hypogaea L., did not occur in the wild, and extensive supportive data now exist on two other cultivated Arachis species still grown in Brazil for food and medicinal use—A. villosulicarpa Hoehne and A. stenosperma Krapov. and W.C. Gregory. Arachis hypogaea seeds likely moved to China and Africa with ancient mariners well before the time of Columbus. After discovery of the Western Hemisphere and the conquests, many forms of A. hypogaea spread to Africa and Asia. Later the cultivated peanut traveled in slave ships from Africa into the southeastern U.S., Central America, and northeast South America, thus returning modified germplasm to the Americas. No evidence has been found that native Americans brought the peanut, along with corn (Zea mays L), to the east coast of North America in pre-Columbian times.