And I don't follow your premise that inherent differences wouldn't be quantitatively consistent. That's how it is with all the other measurable differences between races.
If there was a genetic based IQ difference you would expect the same shift as you see in skin color. But, that's not what happens, thus it's probably not a genetic trait.
Statistically that's not true. I don't understand what you're trying to say.
PS: It's been a few years since I read that finding so it's going to take me a while to find it again.
Edit: Americans that are 1/4 "African" tend to identify themselves as African. This seems odd to me but it's actually the case.
Of course they are.
My roommate in college was half-Haitian half-Portugese and identified more as European. My near 100% African-American buddy I played cards with identified himself as fully black. A half-Carib half-French (black skin tone) girl I knew identified as French. In London, a good friend who is half-Arabic half-Indian identifies equally as Arabic and Indian. My three-quarters Chinese one-quarter Japanese friend raised in Beijing identifies as pure Chinese. I think a 1/4th African 3/4ths European blood person raised in a predominantly black community would identify as black, and raised in a non-black community would identify as European.
All my data is from people who live in international coastal cities though, so maybe it's different in various provinces and less affluent middle-of-country areas.
This can and does vary from country to country--mixed-race Brazilians are considered white in Brazil, but black if they immigrate to the United States.
The African American adolescents had a lower birth weight, a lower verbal IQ, and a higher number of sexual partners than did White adolescents. For each characteristic, the mixed race mean fell between the means of the two parental populations.