One tribe moves out and one tribe stays. History broadens, and philosophy shifts, develops a rift, splits one population from the other . . . and a schism happens, minor or major. It's the way humankind has always proliferated. We go over the next hill, live a few hundred years, change our languages to accommodate things we never saw before--and before we know it, our cousins think we have an accent. Or we think they have a strange attitude. And we don't really understand our cousins any longer.