I have been covering the challenges of African descended DNA analysis in this series of posts. The children of African descent, particularly those in the Americas and the Caribbean do not have a straightforward genetic inheritance. Through the centuries we have inherited a smorgasbord of genetics from wildly different populations. Putting our non-African inheritance to one side, slaves came from many parts of the African continent. And this is at the heart of my conundrum with the generously donated and free admixture tests available on Gedmatch.
I have been scratching my head over why my Gedmatch admixture test results were so completely skewed to West Africa. The results bore no resemblance to my West African heritage shown on a more comprehensive DNA test taken a year ago via Genebase.
I had my suspicions, namely that the people who have given their time to developing these free analytical tools could only create their analytical tools with publicly available admixture data sets. In other words, they had to work with what they could get. The fault, if there was one, lay in the data sets with which they were working. But I needed proof.
The smoking gun came in the form of the Harappa World test on Gedmatch. I am grateful that the developer of Harappa has been so transparent on the blog he created about this test.
I ran the Harappa test and you’ll see the results below:
Again, West Africa is wildly out of proportion to what I know to be true. So I went to the Harappa blog (http://www.harappadna.org) to investigate. And I found background information on the test that would prove to be a goldmine.
The test uses populations from around the world. Which is great for those of us with complex non-African genetic inheritances. I could get an overall sense once again of just how mixed my admixtures really are. Again, looking at the table above, the non-African results are pretty much in line with what I know about my admixture makeup already. There are some omissions to be sure, but those populations weren’t included in the data sets for this test – it’s always a good idea to really read the background information for these tests to understand what world populations have and haven’t been included and what each test has been designed to measure.
Group results that form this test are shown in the bar chart below (click on the images below to see a larger image).
If I’m understanding this bar chart correctly, populations from the Caribbean and the US are influencing the results for West Africa – and not by a little bit either. The inclusion of either of these populations would drastically skew results for West Africa. Together, the weight they place on this result is dramatic. The Caribbean and the US should be their own categories, and not included within West African results. African descended peoples in either region are the children of Africa, not the progenitors.
Not all slaves who arrived in the Americas and the Caribbean came from West Africa, which is another point to consider. Yes, a sizable percentage of African slaves did come from this region. However, one shouldn’t assume that just because you’re African descended and live in these two regions that the larger part of your African DNA inheritance comes from West Africa. I’m a living example of this with the majority of my African DNA arising from Northwest Africa (Tuareg & Berber) with regions such as North, Central and East Africa contributing far more than my inheritance from either South and West Africa.
Again, kudos to Harappa’s creator for his candor and transparency. In his own words:
“…the admixture components do not necessarily represent real ancestral populations. Also, the names I have chosen for the components should be thought of as mnemonics to ease discussion. I chose them based on which populations in my data these components peaked in. They do not tell anything directly about ancestral populations. The best way to look at these admixture results is by comparing individuals and populations.”
This, in the end, answered my question. I would advocate that such an important qualifier should accompany the test itself.
Casting an eye down the bar chart provided above, making note of the various tribes who comprise results for West Africa, there are many who influence this result. Some I have to question. I will take the Kongo, as an example. The larger part of the Kongo admixture (86%) is attributed to West Africa. In actuality, historically, this is a Northeast African tribe. Which is odd as Northeast Africa is only shown as contributing to 5% f this tribe’s admixture. In my Gedmatch DNA test, the Kongo tribe is attributed to Northeast Africa and accounts for roughly 22% of my admixture from Northeast Africa (Egypt is the largest contributor from this region of Africa at 53% via Genebase).
Again, this isn’t a criticism of the person behind the Harappa DNA analysis test. It’s more to do with the originator of the data set that was produced.
I have a strong feeling that this is the reason behind the skewed West African results for the tests I’ve done to-date on Gedmatch.
I have one more Gedmatch test to run and post about. However, what I will say at this point is that a more refined understanding of African admixtures is sorely needed for these kinds of admixture analysis tests. Personally, I would love for someone who understands the intricacies of Africa, its peoples and African admixtures to develop a Pan-African admixture test that is every bit as comprehensive and detailed as the European and Eurasian focused tests found on Gedmatch. That would be an amazing thing indeed.
I’m fortunate. I found a DNA testing service provider that answered this question for me already. My wish is for others to have a refined and accurately reflective picture of their own African genetic inheritance.
I have one last Gedmatch test to report on. It’s the EthioHelix K10 Africa Only Admixture test. In many ways, I saved the best Gedmatch admixture test for African descended peoples to last.