So, there's a biological reason why, even if someone is half and half, they are usually regarded as black and identify it.

Even if someone is perfectly half white and perfectly half black, a lot of dominant traits come from the black half. Because of that, it's very hard to pass as white. I've met folks that can pass as white, but the part of them that's black is much less than 50%.

I was actually just talking to my SO about this tonight and he made a good point. He said that african-american black is very different than africa-black. He said in a way it's very much become like it's own racial group because there is so much mixing with white and other racial groups in the USA that 'black' is now too broad. Black doesn't capture any level of whiteness even though shadeism is a big issue, and it also complete erases the white aspect of a black person's lineage. Society automatically acts like anyone that's mixed is just black, but that kind of forces them to give up, say, 50% of history that they're entitled do. I mean, you can be half Scot and half black and never be treated like you have Scottish heritage.