diffusionist
noun
dif·fu·sion·ist di-ˈfyü-zhə-nəst 
: an anthropologist who emphasizes the role of diffusion in the history of culture rather than independent invention or discovery
diffusionism
di-ˈfyü-zhə-ˌni-zəm
noun diffusionist adjective
Word History
Etymology
diffusion + -ist entry 1, after earlier diffusionist, adjective, and diffusionism (probably after German Diffusionismus)
First Known Use
1920, in the meaning defined above