The topic of extra-continental contact is generally concerned with whether or not any contacting cultures affected the development of Pre-Columbian civilizations. Most Americanist archaeologists favor ideas which promote the approach that cultures in the Americas developed in isolation from the eastern hemisphere. They interpret the archaeological record to show in situ, pristine development in which people interacted across local regions but not across oceans. Most proponents of inter-hemispheric contact advocate diffusionist ideas that interpret American cultural development as having been either dependent on or changed by eastern hemisphere cultures.
A number of diffusionist theories involving ancient visitors are religious-based, mystical or metaphysical. Diffusionism implied by The Book of Mormon holds that a number of Hebraic groups migrated from the Middle East to ancient America. (See Controversies regarding the origin of The Book of Mormon.) Atlantis connections figure in the mysticism of the Rosicrucians and Theosophists. American relationships to the proposed Pacific Oceanic lost continent of Lemuria, also known as Mu, are championed by admirers of James Churchwood. Ideas of extra-terrestrial visits have been proposed, most popularly by Erich Von Danniken. Other theories of contact include proposals involving off-course Shang Dynasty ships, Muslim ships from Asia (see Sung Document), the Chinese fleet led by Zheng He, Afro-Phoenicians, the famous Polynesian proposals of Thor Heyerdahl, and numerous suggestions of Egyptian influence.
Questions as to whether Homo sapiens sapiens has been the only human species to inhabit the Americas have been seriously debated, with the common consensus being that if other species did manage to occupy parts of the Americas, they had no impact on the homo sapiens sapiens cultures that arose in the Americas.
See also: Pre-Columbian trans-Atlantic contact, Diffusion (anthropology)