I've thought about this one a lot, too. What's even more outrageous is when you consider how much inbreeding must be happening in among blacks in inner cities. Think about it. Take a neighborhood like, say, Harlem or south central LA, where the population may live their whole lives. 70+% of black babies are born out-of-wedlock. How many of them do you think know who their father is? How many siblings living in the same house have different fathers? How many black students sitting in the same classroom have the same father and don't even know it? How many of those half-sibling students are going to go on to make babies? Add another layer to all of this when you consider the sexual abuse problem, [that is often incestuous](https://www.mynirvananow.org/files/Toledo_Journal_Child_Abuse_Article_20062.pdf), of the black community. When the fathers are around, they're raping and impregnating their kids. [Over 60% of black girls are abused by black men.](http://www.rolereboot.org/culture-and-politics/details/2014-09-sexual-abuse-code-silence-black-community/index.html) I haven't found a scientific study on this (although I did find [this great Yahoo! Question from six years ago](https://answers.yahoo.com/question/index?qid=20150119065603AAB0ZBT)