I attribute the growth to a greater familiarity with words from reading as literacy rates rose, along with improved access to new words from other sources. The educational level of the population in the South improved tremendously during the century, but the number of differences between the speech of the more educated and less educated speakers remains about the same. So does the importance of race as a factor, despite the repeal of Jim Crow laws and concomitant racial integration in some areas of life. Sex remained a relatively unimportant factor in determining vocabulary choices. Age, race, education, and rurality each account for about 20 percent of the variation in words linked to particular groups in 1990.
Cultural differences run deep between city and country, however.
Not so with the earlier divisions between coastal and upland regions of the South. Our language, as it manifests in various dialects, is a dynamic entity, especially in its words and meanings. As our world changes, so does our speech.