Citation? If this were a well established finding without known flaws in its methodology, I would expect it to come up a lot in race/intelligence discussions, but this is the first I've heard of it.
American "blacks" aren't about half European anyway, they're less than 20% European on average.
Please remember to have no heroes or villains, but this just looks plain bad to be honest. I'm lowering my estimation of the quality of Stephen J. Gould's work in this area.
USA today:
Haha. Humans.
The paper itself: