Senegambian ancestor DNA in the Berry, Fortenberry, Morris, Polk, and Riley settler families of 19th century Mississippi

Location: Lawrence County and Simpson County, Mississippi, United States
Surnames/tags: Berry Polk Fortenberry

I'm a descendent of the Polk, Berry, and Riley families who settled in Lawrence and Simpson Counties in Mississippi, USA in the first half of the 19th century, members of which were all listed as 'white' on census documents and generally understood to be of European descent.

I'm trying to identify an ancestor of Senegambian origin.

Using 23andMe and the AncestryDNA® ThruLines® tool, I've found a number of distant cousins in these families who all appear to have approximately 1% DNA from a Senegambian ancestor.

According to my 23andMe DNA analysis, "You most likely had a third-great-grandparent, fourth-great-grandparent, fifth-great-grandparent, sixth-great-grandparent, or seventh-great- (or greater) grandparent who was 100% Senegambian & Guinean. This person was likely born between 1690 and 1810."

The search has been complicated by an apparent 'double cousin' situation, a closed loop in the extended family tree, and I'm hoping someone can provide new information to shed light.

Here are the key ancestors and relationships as far as I can tell:

7 of the 8 cousins I found, each with approximately 1% Senegambian DNA are descended from the following husband and wife: John Paul Berry (born 1765 in Virginia, died circa 1833-1835 in Simpson County, Mississippi) married to Edith Ann Polk (born c. 1767 in Virginia, died c. 1825-1828 in Simpson County, Mississippi). The marriage took place in Virginia in 1787. Both parties of the marriage were born in Virginia, married in Virginia, and died in Simpson County, Mississippi. These are my fourth-great-grandparents. Their descendants with Senegambian DNA have surnames including Berry, Morris, Riley, Chandler, Sutton, and Blades.

I have tried to identify the parents of John Paul Berry and Edith Ann Polk. These identities and relationships are harder to substantiate at this level, i.e. my fifth-great-grandparents.

John Paul Berry's parents may be John (Jackson?) Berry (Virginia, 1728-1797), and Susannah Schmidt (Smith) (Virginia, 1740-1836).

Edith Ann Polk's parents may be Thomas Polk Jr. (born c. 1737 in Pennsylvania, died 1806 in South Carolina), and Mary Wilson (born c. 1730 to 1740 in Virginia, died c. 1780 in South Carolina).

There is also at least 1 cousin who appears to inherit the 1% Senegambian DNA through a sibling of either John Paul Berry or Edith Ann Polk: Jemima Berry Shivers (born 1770 in Virginia, died 1837 in Simpson County, Mississippi), sister of John Paul Berry, or Joseph Isaac Polk (born 1780 in South Carolina, died 1859 in Lawrence County, Mississippi), brother of Edith Ann Polk. This 1 cousin is the product of intermarriage between a great grandaughter of Joseph Isaac Polk and a 2nd great grandson of Jemima Berry Shivers.

All of these lines trace back to the parents of either John Paul Berry and Jemima Berry Shivers, or to the parents of Edith Ann Polk and Joseph Isaac Polk. I can find nothing to document or suggest that any of these individuals were identifiably Black or African or enslaved or descended from an enslaved person.

At this point, I can't see how to trace the Senegambian DNA back any further. It would appear to come from one of the parents of siblings John Paul Berry and Jemima Berry Shivers, or else from one of the parents of siblings Edith Ann Polk and Joseph Isaac Polk. John Paul Berry and Edith Ann Polk married and produced offspring. Jemima Berry Shivers and Joseph Isaac Polk, siblings of the married couple, were not themselves married to each other, but their distant offspring intermarried, creating a large closed loop in the family tree of Polk, Fortenberry, Shivers, and Berry.

Who was the 100% Senegambian ancestor? It seems unlikely to have been Thomas Polk Jr. or John (Jackson?) Berry. How much is really known about their respective wives, most frequently listed as Mary Wilson and Susannah Schmidt (Smith)? Could one of them have been 100% Senegambian? The documentary evidence for this entire generation seems thin. Or was it one of their parents? Or did one of these produce a child from an undocumented or illegitimate union with an 100% Senegambian person?

Senegambia provided the majority of enslaved people imported into the Americas through the 17th century, and continued exporting large numbers of enslaved people during the 18th and the 19th centuries. Captives played a very important role in the development of rice cultivation in the US South, notably South Carolina and Louisiana (https://www.whitneyplantation.org/history/slavery-in-louisiana/slave-trade-in-louisiana/). Most [Senegalese were] trafficked to South Carolina, Georgia and the Gulf Coast, followed mainly by Virginia and Maryland... probably because [Senegalese] people had the agricultural expertise to make rice plantations flourish, due to the prevalence of rice cultivation in Senegambia and Guinea (https://en.wikipedia.org/wiki/Senegalese_Americans).