Stimulus Diffusion

Stimulus Diffusion can be loosely defined as the spread of a better idea from culture to culture. Though closely related to expansion diffusion, stimulus diffusion can be seen, in laymen's terms as this : Something is a better idea or concept than an existing one (usually from another culture or society) and even though it's not quite perfect, it supercedes that status quo in terms of usefullness, practicality, or simplicity, and thus is adopted by a culture, and diffuses through.
A very basic example of this is the process of agriculture. It has been sumrised that agriculture originated somewhere in the Middle East, and then spread to all of Eurasia, and then to all of the world.
It could be said then, hypothetically, that as long as cultures continue to interact, and exchange ideas, the best, most useful way of doing things will eventually transfer, and reduce some of the cultural differences that we see today.