Yes, we are all technically African. In the sense that modern humans evolved in Africa. Our entire evolutionary history as far as you would like to date back (whether that be 200,00 years with the rise of modern humans or 8 millions years with the emergence of hominins) took place in Africa (of course it's all semantic - if you wanted to date our ancestors back to the emergence of monkeys then "we are all Asian" or if you want to date us back to the emergence of the first primates than "we are all northern North American and European" or if you want to date us back to the emergence of the first known life "we are all Australian"!).

Back to humans. That being said, of course the last 100,000 years of our existence has not solely been African. There was an immense bottleneck that took place when modern humans finally left Africa (the result is that >90% of modern human genetic variation is in Africa).

It is a little surprising that this man's genetic results suggest that he is "14% Sub-Saharan African. Razib Khan (Gene Expression blogger) doubts it:

If Craig Cobb, the white supremacist, is ~14% Sub-Saharan African, he’s in the less than 0.1% of white Americans with this sort of pattern.

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the reality is that European Americans with relatively well documented histories usually do not have a high probability of having African ancestry. And if they do, 14% is a great deal. I have seen this among my friends (or more honestly, 5-10%, which is not far off), but that was due to a cryptic (though somewhat known within the family) non-paternity event.

Different genetic tests could most definitely reveal a different percentage. And I'm not going to vouch for a genetic test done by 23 and Me for a daytime talk show. Especially since it gave results that are statistically impossible and produced the desired result for the highest degree of controversy (what a coincidence!). We know from American history that the disgusting "one drop rule" prevented anyone with any black ancestry from really becoming integrated within "white" society (much less a "white" family) (unlike in Latin America where the racial categories and boundaries were much more fluid and less restricting). White Americans (U.S.) always drew a very firm line in the proverbial sand between "white" and "black" (of course it's far more likely for an "African American" to have a substantial part of their genetic heritage to be "European").

From my perspective 23 and Me tests (like the one taken by Cobb) are really misleading science. It's not necessarily pseudoscience, but they definitely make statements that, from a scientific perspective, are really difficult to say with a high degree of certainty (or any certainty) (and yet they always make very definitive statements after a test).

The reason it is so hard to say anything about genetic backgrounds with a high degree of certainty is because there is no such thing as biological races and therefore the "percentage" of your genome that is descended from a certain culturally constructed group will change based on your classification scheme (i.e., how are you grouping people? sub-Saharan African? Black? African? Tutsi? Bantu? Who gets into what category and why? What makes sub-Saharan African a category worth measuring? What is considered "black"? As I said there is more genetic diversity in Africa than any other continent. If sub-Saharan African is a category of humanity than the only logical further division is with "rest of humanity". In which case the title of articles should read "non-African discovered to be 14% African").

Also, if you go back just 8 generations you have well over 200 ancestors and could have a genome mixed of all of them equally. So if you go back only a short period of time you probably have ancestors on every continent (even though they may be disproportionately concentrated on some continents over others). Calculating any further back than 10-12 generations is essentially pointless. The exponential pace at which your ancestors increase well past this point makes all of humanity your ancestors.

As a result a lot of genetic testing related to "ethnic" and "continental" ancestral heritage is really sensationalized (especially when it comes to saying that someone is a certain percentage "of something"). There are no such thing as "sub-Saharan African" genes (there are certain genes that will arise with a higher frequency in different populations and some genes that may be unique to certain populations - but there is no such things as a "sub-Saharan African" group.

So what does it mean to be "14% sub-Saharan African"? Hm. IMO it means nothing. I guess it means that a lot of websites will run headlines that catch peoples attention and generates controversy.