“Or between a yorkie and a Great dane, but they’re the same species, Canis lupus familiaris”
AND ! Other than size I think we can all allow some ‘breeds’ much smarter than others ??.....Altho all same species ?
Let's set some common agreements first -- you agree that all humans alive today are of the same species? I would also argue of the same sub-species, but since that's so vague beyond "they can reproduce and produce fertile offspring", it's not worth asking
To your question "some breeds of dog are much smarter than others" - you of course want to ask if some groups of humans are smarter than others - the answer isn't simple, but:
- The average of some groups of humans are smarter / taller / stronger / faster / etc. than other groups, but that is the average. There are dumb Ashkenazi Jews and there are Ghanians who can't run or jump. Similarly, you will find exceptional people who are brilliant but not of Ashkenazi Jewish or Asian background (at least not mainly)
- The "groups" are difficult to determine. you want to say "blacks" - but in the US these are so mixed and you have blacks from Africa tossed in, so it's difficult to state. And, in Africa proper itself, you have Ethiopians who are very intelligent and you have people related to the Zulus who aren't.
- The tendencies show themselves in less than a dozen generations if there is external pressure. Ashkenazi Jews for instance are genetically similar to Mizrahi Jews or Cochin Jews, yet Ashkenazi are on average smarter. The reason is that for 1000 years they were not allowed to carry out any physical trades and it exacerbated after the middle ages when the only ones who prospered were the ones who could think. Cochin Jews didn't have that pressure
As to African-Americans, I believe a lot is due to culture as AAs have a lot of genetics from various white and native American groups.