In its most general sense anthropologists define diffusion as the flow of an idea or artefact from one culture to another. In the late 19th century, many proposed diffusion as a theory to explain all major similarities between widely dispersed cultures. The most famous proponent of this theory was William Graham Sumner, who argued that civilization first formed in ancient Egypt and then diffused to other places. A more recent proponent of this theory was Thor Heyerdahl, who argued that elements of Polynesian culture have their origins in ancient Peru.
The theory of diffusion has been criticized for being ethnocentric; it implies that people living in different places are not equally capable of innovation; that some people innovate and others copy. It has also been criticized for being speculative.
Today most anthropologists accept the fact that diffusion occurs, but reject the theory of diffusion as an explanation for cross-cultural similarities. The main criticism is that even when diffusion occurs, the theory does not explain why it occurs -- in other words, why some ideas or artefacts diffuse, and others do not. Moreover, it does not explain how in the course of diffusion traits may be assigned new uses and meanings.
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