While the concept of diffusion is well accepted in general, conjectures about the existence or the extent of diffusion in some specific contexts have been hotly disputed. An example of such disputes is the proposal by Thor Heyerdahl that similarities between the culture of Polynesia and the pre-Columbian civilizations of the Andes are due to diffusion from the latter to the former—a theory that currently has few supporters among professional anthropologists. Heyerdahl's theory of Polynesian origins has not gained acceptance among anthropologists. Major contributors to inter-cultural diffusion research and theory include: