A new study from Stanford University has unveiled significant insights into the family connections among African Americans, demonstrating that the term “cousin” may reflect deeper ancestral ties than previously understood. Published in the journal The American Statistician on February 7, 2026, the research employs a mathematical model to explore the familial relationships that can be traced back to ancestors who lived between 185 and 410 years ago.
The study addresses the historical impact of slavery on African American genealogy, an area often obscured by inadequate record-keeping prior to the 1870 census. Researchers found that for two randomly selected African Americans born between 1960 and 1965, there is a probability between 19% and 31% that they share at least one ancestor who was forcibly transported across the Atlantic during the Transatlantic Slave Trade. Notably, this probability increases for individuals born between 1985 and 1990, where the likelihood of shared ancestry exceeds 50%.
Noah Rosenberg, the study’s senior author and a professor of biology at Stanford, emphasized the significance of these findings. He stated, “We used a mathematical model of genealogies to see what might be found in families where the precise story is not known.” Rosenberg noted that the high probability of shared ancestry is remarkable not only for understanding the relatedness of the African American population but also for illuminating aspects of American demographic history.
The researchers developed their model using a concept known as “the birthday problem,” a statistical framework often introduced in educational settings to illustrate probability. This problem shows that in a group of 23 students, the likelihood of at least two sharing the same birthday exceeds 50%. When applied to the ancestry study, Rosenberg and his team identified analogous probabilities regarding individuals whose ancestors experienced the same historical trauma.
The research estimates that African Americans born in the early 1960s each have approximately 300 ancestors among the estimated 400,000 to 500,000 Africans transported to North America from the early 1600s to 1860. By analyzing the overlap between these ancestral groups, the study sheds light on the interconnectedness of the African American community. As researchers examined subsequent generations, the number of ancestors increased, heightening the chances of sharing an ancestor with contemporaries.
Other studies have attempted to bridge the knowledge gaps in African American ancestry through genetic analysis. An earlier investigation from Rosenberg’s lab provided estimates of the number of African and European genealogical ancestors in typical family trees. Although the current study does not establish direct connections between specific descendants and ancestors, it offers valuable insights into shared heritage.
“In most cases, the question of whether two specific people have a shared transported ancestor cannot be directly answered,” Rosenberg explained. “Many aspects of the history of slavery led to profound loss of genealogical information. A mathematical model therefore has potential to make a meaningful contribution.”
This research highlights the importance of mathematical modeling in understanding complex historical narratives, providing a new perspective on the genealogical landscape of African Americans and emphasizing the lasting impact of history on contemporary identities. The findings may encourage further exploration into the intricate tapestry of family ties within the African American community, fostering a deeper appreciation for shared ancestry and heritage.
