Addressing the feasibility of people of African descent finding living African relatives using direct-to-consumer genetic testing

Abstract

People of African descent use direct-to-consumer genomics services such as 23andMe and AncestryDNA for various family histories and health reasons, including identifying and interacting with the previously unknown living African genetic relatives. In this commentary, I argue that it is reasonable to consider that cousin pairs consisting of an African person and a descendant of an African person enslaved in the Americans during the Transatlantic Slave Trade (i.e., a person of African descent) have genealogical ancestors recent enough to be detected using autosomal DNA testing where the pair has shared ancestors in the range of 20–6 generations ago from the present.

African ancestral familial ties were disrupted for those in the African diaspora (referred to as “people of African descent”) whose ancestral displacement was due to the Transatlantic Slave Trade (Butler, 2001). Notwithstanding, people of African descent use direct-to-consumer genomics services such as 23andMe and AncestryDNA for various family histories and health reasons, including identifying and interacting with the previously unknown African genetic relatives. To be clear, in moving beyond the biogeographical ancestry estimates to use the list of DNA matches provided by companies, they are finding African relatives. Based on preliminary interview data analysis of seven self-identified African Americans who used genetic genealogy to identify an African relative (David, 2022), this genetic relatedness is interpreted as finding biological relatives who descended from the same genetic genealogical ancestors in Africa. Discovering relatedness in this one-to-one cousinship was significant because it signified a type of family reunification after the mass trauma of their genealogical ancestors being separated from their families during the Transatlantic Slave Trade (TST).

When I shared this reunification context with academic audiences and claimed that families separated during the TST were reuniting using genetic genealogy, I was surprised at the initial criticisms I received. Much of the criticisms and misconceptions appeared to be due to people not recognizing the utility of the existing tools for people of African descent to identify living African relatives. For example, some assumed I was referring to using the results from African Ancestry, Inc. (African Ancestry, Inc., 2018), a popular company among people of African descent for offering consumers African ethnic origins based on mitochondrial DNA (mtDNA) and Y chromosome (Y-DNA) testing. Their skepticism and general regard for those results fueled their disregard for my claim about family reunifications even though the participants in my research did not claim to find relatives from the results of African Ancestry, Inc. products or even mtDNA or Y-DNA testing. On other occasions, after explaining the use of autosomal DNA testing to find evidence of relatedness, some said that finding this one-to-one relatedness was not possible or was too difficult.

Given that people of African descent are already finding African relatives using autosomal DNA testing with commercial genetic genealogy services, it is reasonable to consider that cousin pairs consisting of an African person and a person of African descent have genealogical ancestors recent enough to be detected using autosomal DNA testing in academic research where the pair has shared ancestors in the range of 20–6 generations ago from the present. Undeniably, the duration of the TST (i.e., 20–6 generations ago (Micheletti et al., 2020)) is recent enough to be captured in identical-by-descent (IBD) segment sharing among Africans and descendants of enslaved Africans in the Americas. In this commentary, I address several criticisms and misconceptions while discussing the reasonableness of people of African descent being able to use autosomal genetic genealogy to find living African relatives whose ancestors were taken from during or within a few generations before the TST and to infer a genetic genealogy tree with some African founders within 10 generations from the present.

Attributes of IBD segments are used to estimate the time to the most recent ancestor (TMRCA), which can be applied to estimating the TMRCA for an African and person of African descent cousin pair (Browning & Browning, 2012; Henn et al., 2012). For example, given IBD sharing of 7 cM among members of the same population group, the expected TMRCA is 21.4 generations ago; given IBD sharing of 8 cM and 15 cM, the expected TMRCA is 18.8 and 10.0 generations ago, respectively (Baharian et al., 2016, p. 19).

Whereas a thorough discussion about the quality of genomic data and the performance of IBD detection methods are beyond the scope of this article, suffice it to say that there are available tools such as Refined IBD (Browning & Browning, 2013) that can accurately detect IBD segments at a minimum of 2 cM in phased data (i.e., genotype data ordered on the chromosome by parent) and other methods to detect segments at a minimum of 7 cM in unphased data (Browning & Browning, 2013; Henn et al., 2012). Consequently, for as much as there are tools to identify 2 cM IBD segments and assuming that the TST was within the last 75 generations (which it was), the genetic genealogy connecting families that were separated during the TST can be inferred.

According to the Trans-Atlantic Slave Trade Database, human trafficking within the TST occurred between 1525 (i.e., the first slave voyage) and 1866 (i.e., the last slave voyage). During that time, approximately 12.5 million persons were taken from Africa, heading toward various diasporic locations (Eltis, 2018). Using a conversion of 1 generation equaling 25 years, the TST began roughly around 20 generations ago and ended 6 generations ago from the present day. For the U.S. elderly population, that duration would roughly begin at 18 and end 4 generations ago. From the perspective of using IBD sharing to estimate TMRCA, IBD sharing of 7.5 cM has an estimated TMRCA of 20 generations ago, and 25 cM has an estimated TMRCA of 6 generations ago (Baharian et al., 2016). In other words, assuming adequate quality control measures were taken, IBD sharing of 7.5–25 cM on average captures the duration of 6–20 generations ago during the TST period. Whereas the estimated TMRCA may be precise to within a few generations of accurate, having these clusters of genetic relatives is still highly informative toward building a more cohesive family history for people of African descent who descended from the enslaved.

A study conducted by Micheletti et al. (2020) explored IBD genetic relatedness between Africans and people in the Americas with some African ancestry and found that 88%–91% of their study sample of the U.S. diasporic individuals shared at least one IBD segment of at least 5 cM with African individuals from each of the five African regions in the study. A 5 cM segment has an expected TMRCA of 30 generations ago on average (Baharian et al., 2016), meaning that for most of the people of African descent in the study sample, there was at least one African relative in the study sample that connected them to a genealogical ancestor from Africa a few generations before the start of the TST on average. Though the authors of that study did not provide the IBD genetic length data, they estimated that the most likely TMRCA between the diasporic individuals in the United States and Africans from the Gold Coast region sample was 16–17 generations ago, the Bight of Benin 13–14 generations ago, and Central Africa regions about 13 generations ago (Micheletti et al., 2020).

The Micheletti et al.'s (2020) study shows that there is detectable IBD segment sharing between Africans and people of African descent within the relevant timeframe coinciding with the TST, given a large enough database of testers or a relevantly sampled database, as illustrated by social media posts from people of African descent claiming to have found African relatives in their results. There is a low probability of IBD sharing among randomly selected individuals (Kong et al., 2008). However, given a large enough or relevantly sampled database, individuals will likely find IBD-segment-sharing relatives from multiple regions across sub-Saharan Africa. Unfortunately, the publication of Micheletti et al.'s (2020) study did not provide the IBD segment genetic lengths, which would have been informative because the predictive accuracy for TMRCA differs by genetic length and other characteristics (Jewett et al., 2021). Still, the main takeaway is that if there is IBD relatedness between consumers and individuals in a reference panel not designed for such purposes or specially selected African individuals for their study, it is reasonable for a person of African descent to find at least one African genetic relative in a large consumer coverage area serving African nationals or from strategic sampling in academic research.

Human trafficking in the TST occurred over a duration of 6–20 generations ago from the present day (Eltis, 2018). This timeframe in generations coincides with outer bounds IBD sharing of 7 cM (expected TMRCA of 21.4 generations) and 25 cM (expected TMRCA of 6.0 generations) among present-day descendants (Baharian et al., 2016). With adequate quality control measures, including family-based phasing, IBD segments as low as 3 cM can be used to infer a 10-generation genetic genealogy of Africans and people of African descent whose African ancestors were separated in Africa during the TST. Furthermore, it is reasonable to expect that people of African descent would find African relatives using commercially available autosomal genetic genealogy testing services where the minimum threshold for reporting is 7 or 8 cM. Whether found by citizen scientist genetic genealogists or academic researchers, the IBD sharing and TMRCA between Africans and people of African descent is both genealogically and historically meaningful.

Continental African families separated during the Transatlantic Slave Trade are reuniting through their descendants' use of genetic genealogy. It is possible to find genealogical relatedness between Africans and people of African descent with layered evidence of multiple distant cousins sharing the same pair of ancestors to reduce uncertainty in the results. Strategies and technologies such as strategic sampling and using IBD detection within very large databases contribute to inferring a genetic family tree that includes African and African diaspora cousins. Considering the work of inferring genetic family trees among Africans and people of African descent, it is important to note that genetic genealogy and social interactions among Africans and African Americans have psychosocial implications in identity development throughout adulthood (David, 2022).