Flora, of course, first you have to define which of the many black dialects you are referring to when you discuss “talking black.”
(I’m not sure what you meant about not all blacks having an African origin. An immigrant from Jamaica, Barbados, or Trinidad will probably speak with an accent modified by the Queen’s English, but they would still have many of the African speech patterns that were brought over when their ancestors were enslaved on those islands–having been imported from Africa.)
The throatier and less nasal voice that blacks use regardless of (most) accents very likely does come from the African speech patterns that they brought from home and handed to their children. In the same way, Asians with accents tend to sound even more nasal than Europeans because those are the tones that their languages emphasize.
Europeans (and, later, Asians) made a concerted effort after the 1880’s or 1890’s to assimilate. Prior to that, many immigrant cultures actually maintained their original tongues. My family still has stories of the time in the 1890’s when one of my ancestral matriarchs announced one day that the family would henceforth speak English (after speaking German within their American households for around fifty years). The assimilation process was hastened by government and educational authorities who set up special programs from the 1890’s through the 1920’s (when we barred the door to immigrants) to encourage everyone to join in the “melting pot” and become Americans.
Blacks never had that opportunity to assimilate until rather recently. Even when they left the share-crop farms of the South and moved to the industrial North, they were isolated in ghettoes and no special efforts were extended to them to be like “the rest of us.” Language patterns that had developed among them during the slave period continued after it because the communities were not integrating with the white community and there was no pressure to “sound like” their separated neighbors. It was probably a good tactic during the periods of slavery, and then Jim Crow, to have a language that was based on American English but was sufficiently different to prevent the local slave-holders or their successors from listening in on any conversations.
(On the west coast, some aspects of ghetto attitudes had an impact on Asian immigrants right up until WWII, after which they were allowed access to the mainstream and baby boomer third and fourth generation Asian-Americans are the first to consistently speak “without an accent”; the same can be found among the Irish and the Jews of the East coast, where third and fourth generation immigrants had culturally noticeable accents until around WWII.
You mentioned an Eastern European background; Polish is a strong immigrant population in Metro Detroit. In metropolitan Detroit, there are many people whose speech is influenced by their Polish forebears. It is stronger in Wyandotte or Warren than in Sterling Heights, (or the pure Kentuckian of Hazel Park or Ypsilanti), but an attentive ear can still pick up those strains. And the fact that you hear less Polish-American in Rochester Hills is a result of the mixing of the German, Irish, Italian, and Polish, accents with the accent of the original New Yorkers who settled there and with the people who came from all over the U.S. and Canada for Henry Ford’s $5.00/day wage.
I went to school with a number of guys whose speech reflected Polish or Italian backgrounds, but who were all born in the 1950’s and whose grandparents all immigrated in the 1890’s or 1900’s. Their kids, by and large, have only a SouthEast Michigan accent, but it has taken 100 years to get there for many families.
Confined to specific areas until the early 1970’s, the black population of Metro Detroit has not had the fifty years of mixing that the Poles and Italians have had.
Blacks who have tried (through scholarship or the entertainment industry) to leave the ghettoes behind, often have tried to assimilate, and have modified their speech patterns to sound more like the majority. That has gone on throughout this century, but has become more frequent with the collapse of Jim Crow and his Northern cousins, redlining, etc.
Is Black Non-Standard English (or Ebonics) generally a sign of lower education levels? It probably is a decent indicator. Although there are many educated blacks, today, who probably still maintain their accent for the same cultural reasons that third generation European immigrants often try to go back and capture the original language (after the second and third generations rejected it in favor of Americanization).
Tom~