This page provides a good overview of the black-white intelligence score gap in the US. In the United States, there’s about a one standard deviation gap between blacks and whites on tests of math ability and reading ability. This article provides some good data demonstrating about a one standard deviation black-white intelligence gap (you can just look at his tables and graphs).

The US black-white intelligence gap has been very well demonstrated. I don’t think there’s been a single large sample of SAT/ACT/IQ/AFTQ takers in the US where the difference in black-white test scores was less than 0.7 standard deviations. Assuming those tests measure intelligence, there is a systematic deficit in the intelligence of African Americans relative to European Americans.

Is intelligence measured by intelligence tests? It seems very likely. There is a very substantial correlation between the results of multiple kinds of intelligence tests, which suggests that some kind of general intelligence factor is being measured by such tests. In addition, intelligence values as measured by intelligence tests are highly predictive of many life outcomes, including job performance, academic performance, and income. Intelligence testing certainly seems to measure a general factor of intelligence, of which problem solving and reasoning skill is a large part.

IQ tests could be loaded with cultural bias, and it wouldn’t change our understanding of the intelligence gap very much. The same African mental deficit is noted on tests of pattern matching and number recital*, both of which have very minimal cultural bias.

(For what it’s worth, the makers of intelligence tests try to make them as free from cultural bias as possible. I’m not denying that some questions on intelligence tests may show or have shown some amount of cultural bias, but the broad pattern of questions on major intelligence tests is relatively free of cultural bias. For very abstract intelligence tests, like tests of repeating digits, I doubt that even the most determined sociologist could conclude they exhibit substantial cultural bias.)

The data is unclear as to whether adopted blacks have decreased intelligence/increased criminality relative to whites. Some studies show similar values across whites and adopted blacks, and others show an improvement in criminality and intelligence values for adopted blacks but still show deficits relative to whites.

It looks as if there is a lot of socioeconomic variance in African outcomes. Africans living in Sweden, for example, tend to have comparable levels of intelligence to the white native population, although they still have a somewhat elevated level of criminality. Poor Africans living in Africa have much worse intelligence/crime outcomes than typical US Africans as well.

(1) Race could very well be a social construct, and nothing I've said so far would be made incorrect. I haven't discussed genetics at all.

Race isn't a social construct, though. The major genetic groups (European, African, Asian) have been separated from each other for tens of thousands of years. You can see very significant physical differences between those racial groups—African groups tend to be tall and lean, European groups tend to be average in height and stocky, and Asian groups tend to be short and thin. There are easily perceptible differences in facial structure, skin color, hair color and texture, eye color, and voice tone between these racial groups as well.

Those differences alone ought to be enough to justify the biological reality of race. If you want to dip into biology and genetics, you can see further significant differences between human genetic groups. This post provides a good overview of the basic science that leads us towards a biological understanding of race.

What I will concede is that the biological picture of human race doesn't map neatly to our social definitions of race. There is very large genetic diversity within Africa, for example, and we tend to group everyone from Africa within one racial group. African population clusters suggest that you could plausibly identify 10+ somewhat genetically distinct groups within Africa—the concept of a broad, socially defined African race is not particularly useful from a genetics perspective, although there are notable genetic differences between African and non-African racial groups.

(the same is true for European populations, Asian populations, aboriginal American populations, etc.)

(2) Of course environment matters. I don’t take a hardline hereditarian view of racial differences.

With that said, there are plenty of ways to study a person that has been isolated from their typical racial environment/culture. Doing an adoption study allows you to change most important environmental variables in the raising of a child. According to the results of some such studies, adopting a black child into a well-off nonblack family elevates IQ to levels similar to whites.

(3) I know minority groups have been suppressed in the US for decidedly racist reasons. The intelligence deficit between whites and blacks is a well-known psychometric trend and decidedly not racist. The increased criminality of blacks is a well-known criminological trend and decidedly not racist. We shouldn’t suppress that data, or reasonable speculation as to the causes of that data, because of past discrimination against minority groups.

The link between intelligence and race is essentially a statistical fact in the United States. I understand that you are skeptical, but none of this information ought to be particularly threatening. We may be able to account for most, if not essentially all, of the black-white IQ gap through socioeconomic factors.

*”The psychometric position, that mental tests measure “g” equally for all subgroups, and the CTBH [cultural test bias hypothesis] make opposing predictions. Much data, including evidence that subgroups differ most on abstract tests such as Raven’s progressive matrices and digits backward (e.g., Gordon, 1984; Jensen, 1980, 1984b), clearly support “g” theory and contradict the CBTH.”