You're really overthinking things here. People that demonstrate increased frontal lobe functioning think about the consequences of their actions and are apt to plan shit out. They're generally going to be observed to be more intelligent than their hindbrain dominant coutnerparts because they're more than likely have taken their education serious done their homeword, studied for tests, etc. That's different than IQ but apparently everyone here except for you knew what I meant. If you can't see that the prototypical nerd is not inherently great at stuff like dancing you really need to get out more. Considering you're the same guy who asked what a black person is I shouldn't be surprised.
Of course the prototypical nerd is bad at dancing. That's part of being a prototypical nerd -- social awkwardness. But not all people who are good in school or good at taking tests are prototypical nerds. In fact, most probably aren't. Some of the best dancers that I've known in my life have also been brilliant students, good at standardized tests, etc. These are people who can plan, delay gratification, dedicate themselves to something and focus on getting better at it over time. Some have dedicated themselves to dancing so they're really good dancers. Surprise!
Most of those good dancers are girls because girls are less likely to get called fags for dancing when they're younger, so they get a head start on PRACTICING dance. Dudes from cultures where male dancing is appreciated may be school-smart as shit and also good dancers because -- surprise! -- they started dancing earlier, got positive encouragement to dance and PRACTICED a lot. Even if totally informally, they got encouraged to move to music as little kids so they learned how to do it without looking like spazzes. See: lots of Brazilians.
"Black" a social construct that means something like, "of African descent," and so is useless as a basis for comparing "inherent" traits. If you looked at a black guy from Detroit and a Kenyan walking down the street, you'd call them both black (so would I, we're both American so that's what we see). But there is probably less cultural and genetic similarity between the two of them than between you and me or me and Vladimir Putin. That's the point I was trying to make but which was apparently lost. And that's why the psoas study you cited is so silly -- "black" has no genetic meaning. It's interesting that the black group had bigger PMA's than the white group, but not because they're black.