Types of Diffusion
Ideas spread in different ways, and knowing which type is happening tells you something real: whether it moved with people, jumped straight to influential places, spread through ordinary contact, or changed shape along the way.
Relocation diffusion happens when people physically move and carry a cultural trait with them to a new place — a religion arriving with immigrants is the clearest example. Expansion diffusion is different: the idea spreads outward from its hearth while staying just as strong in the original source area, since nobody has to move for it to reach new people.
Expansion diffusion itself comes in three flavors. Contagious diffusion spreads rapidly through close, widespread contact, regardless of any hierarchy — a rumor or a virus moving through a population. Hierarchical diffusion moves from larger, more influential places or people down to smaller, less influential ones — a fashion trend starting in a major city before reaching small towns.
Stimulus diffusion is the trickiest of the three: the underlying idea spreads and gets adopted, but its exact form changes to fit local circumstances. When Cherokee leader Sequoyah encountered European written language, he didn’t adopt the Latin alphabet — he invented an entirely original Cherokee writing system inspired by the concept of writing itself. A modern equivalent: a global fast-food chain spreading its core concept everywhere while reworking its actual menu for each local market.