A few reasons that the percentages in your ethnic-ancestry breakdown may change over time.
Dear Professor Gates:
I did DNA testing through the site African DNA. Initially it showed I had 82 percent West African ancestry, 10 percent European and the rest “Middle Eastern.” However, I recently received updated results from Family Tree DNA (which appears to be associated with African DNA) to show 83 percent West African ancestry, 5 percent East Indian, 2 percent North African, 5 percent East African, 5 percent South African and 8 percent European ancestry. Can you please tell me why the percentages would change? —Frances Elizabeth Williams
What you experienced actually is a common occurrence. I reached out to Joanna Mountain, Ph.D., senior director of research for 23andMe, which also provides DNA-testing services, to explain why the revision may have occurred.
She told me in an email that she cannot address your ancestry-estimate changes specifically, since they were done by Family Tree DNA, but she did say this:
Speaking more generally, there are two main reasons that such estimates change over time:
1. The reference data to which the customer’s data are compared have been updated/changed.
2. The algorithm for estimating the ancestry proportions based on this comparison of the customer to the reference data has changed.
One hopes that either of these types of changes leads to more accurate estimates of a person’s ancestry proportions.
In other words, your testing service may have received additional or revised information since your initial test results were processed and updated your admixture estimates accordingly. Alternatively (or in addition), the formula used to estimate your admixture may have been updated.
The test results you sent us came from FTDNA, with which I partnered in 2006 to create African DNA. A message on the FTDNA website about the latest version of the myOrigins ancestry results, dated April 7, 2017, explains how estimates might change:
Our Recent update of myOrigins 2.0 has added to and refined our population clusters based on new research and new reference populations that have been collected and published since the myOrigins feature was first released in 2014.
These new reference populations may have caused some of your Regional Ancestry clusters to change or your percentages to fluctuate. This is due to how your DNA matches with these newly defined clusters. We understand that these changes can seem big; however, please keep in mind that these population clusters are meant to reflect regions rather than, often changing, geopolitical borders …
Seeing your results change does not mean that they were incorrect before, but rather, that with more research and the addition of more reference populations we are able to paint a clearer picture of your genetic tapestry. As our database grows, we are able to gain a better understanding of the unique genetic variation for each of our reference populations and even add new reference populations to our existing regions. We will also share these advances with you and continue to refine your results.
For more information, you can reach out to FTDNA directly.
Henry Louis Gates Jr. is the Alphonse Fletcher University Professor and founding director of the Hutchins Center for African and African American Research at Harvard University. He is also chairman of The Root. Follow him on Twitter and Facebook.
Send your questions about tracing your own roots to TracingYourRoots@theroot.com.