Language Development.

As the Paleolithic ancestors of native North Americans spread across the continent in the wake of retreating ice fields after 7000 B.C., they encountered a vast array of new environments and ecosystems. During the next eight millennia free-wandering bands adapted to these new environments, and their movements became increasingly restricted to welldefined territories. As language communities migrated and grew, portions of them split off and moved on. Over time, physical separation, combined with adaptation to different environments and contact with new and unrelated bands, led to increasing linguistic and cultural divergence between subgroups of formerly unified language communities. Together these evolutionary linguistic descendants of a single, common protolanguage constitute a language family and are said to be genetically related to one another. The more closely related two languages are and the higher the degree of mutual intelligibility, the more...