The figures on the left show how salt diffuses through a bathtub of water. In some respects the migration of people in prehistoric times owing to the spread of agriculture might be considered a diffusion- like process. The figures on the right show concentrations of farming settlements in 8000 BC, 5000 BC, and 1000 BC. The traces of this farming expansion can be seen today in the genetic structure of human populations, as well as in the common features of most of the languages spoken in Europe and Asia; their common ancestor was the Indo-European language spoken by the first farmers.
This research is reported in an upcoming issue of Physical Review Letters.