A Washington Post article late last week by Susan Svrluga essentially makes this point: if we look hard enough and far enough into our background, we are all black.
I’ve never bought the idea that ethnic origin is very important, and somewhat scoff at silly TV ads about wearing kilts and giving up lederhausen.
There’s an MIT article that explains how we may all have a common maternal ancestor in Africa through X chromosomes, but Y chromosomes and mitochondrial DNA complicate the picture. The article denies that “white” people have maternal Neanderthal DNA, but interbreeding with other hominids was possible, But “white people” have arisen several times in areas far from the equator, when they needed to be able to make Vitamin D with their own bodies more easily in lower sunlight.
The idea of race itself has almost no real meaning in human biology.
Here’s another story from the Washington Post, that a lot of southern whites have a little black ancestry from slave owner behavior.
Admittedly, we can aggregate people by "looks", but there is a lot more than just amount of skin pigment (which safely absorbs ultraviolet light and is needed in equatorial regions when people don't have clothes.)