Speaking of Arthur Jensen, Occidentalist has a table listing all 40 academic studies he could find of the white-black gap in average IQ in the U.S. They range from 1918, when it was measured at 17 points, to 2008, when it was found to be 16 points. So, don't let anybody tell you The Gap hasn't closed over the last 90 years.
Seriously, is there anything in the human sciences more stable than La Griffe's Fundamental Constant of American Sociology? It's really odd when you stop to think about how stable it has been. I suspect that differences in average height have changed significantly more over the generations. For example, when I was a kid, the Dutch weren't particularly tall, not the way they are now.
Except this ...
Indeed, I'm wondering whether there isn't some kind of behavioral feedback at work regarding IQ that somehow keeps The Gap about the same. I don't have any candidates in mind for what that stabilizing mechanism might be, but it's worth considering.