The issues with Murray's claims is that he sucks at stats and has been basing his race and IQ positions on his questionable grasp of stats, apparent misunderstanding of heritability, and his cherry-picking of very questionable data for nearly 30 years. There's also the issue that the "data" he claims to have on registered nurse IQ has never been published and he's not made it publically available, even though he apparently mentions in his book that he has collected it. We're basically just supposed to take his word for it. I don't and I think he needs to produce that data or STFU.
But, let's suppose that he were to release that data and it did show that white registered nurses were "a dozen IQ points" higher than black registered nurses, it would suffer from the same misguided (or misinformed) theoretical and statistical errors that his overall arguments suffer from: theoretical = his ignorance of what heritability means/implies; statistical =
conditioning on a collider.
In terms of his ignorance of what heritability actually means, one of the chief claims he keeps peddling is that since intelligence is roughly 60% heritable in adults, that means that intelligence is largely genetic, and therefore the IQ gaps between racial groups is largely genetic (i.e., races with higher average IQs have better genes). He used this same shitty idea to argue against welfare and Latin American immigration in The Bell Curve.
What he fails to understand...even after 30 years, which should've been plenty of time for him to study up on this...is that adult heritability of IQ is drastically different than heritability in childhood, and that childhood is crucial for developing/establishing adult intelligence. Here's what I mean:
Intelligence is roughly 60% "heritable" in adults (i.e., 60% of the variance in IQ scores can be explained by genetic factors and 40% is explained by environmental factors. This is established via twin studies, both identical and fraternal). However, it is closer to the oppposite in childhood (i.e., 40% to 45% genetic with 55% to 60% environmental). Environment has a stronger effect on intelligence when you're a kid because that's when you're going to school and learning and your brain is growing as it absorbs all of this new info and learns all these new skills. The environments in childhood are more dynamic. Low income kids have less access to good schools, good learning environments, good nutrition for their developing brains, and good home environments than middle and upper class kids. So, these crappier educational and home environments will have a strong negative impact on intellectual development in low income kids relative to their middle and upper class cohorts. This is true of low SES no matter what racial or ethnic group one belongs to.
So, the low SES kids grow up with lower IQs, largely due to these worse childhood environments. Now they're adults, and their environment has much less of an impact on their intelligence (because most people stop going to school when they hit 18, so they're no longer in an educationally dynamic environment as adults). Therefore, since their environment is more stable, it explains less of the variance in intelligence scores. Thus, "genetics" claims a larger share of that variance. But, "genetics," at least in this case, might also be representing accumulated prior educational experience.
Unfortunately,
lower socioeconomic status is significantly related to large differences in intelligence compared to higher SES. There's also much wider variance in IQ within groups than between groups. What that means is that the range of IQ scores within each racial group (on average) are larger than the differences in IQ scores between each racial group (this is more prominent in groups with larger proportions of low SES). This larger within-group variance can contribute to lower group-level mean IQ scores, which can be somewhat misleading.
Also unfortunately, black kids are overrepresented in lower income households relative to hispanic, white, and asian households. So, a larger proportion of black kids (relative to white and asian) will not have access to the more productive and efficient educational environments that higher income groups have access to. Which means they'll get shittier educations, which means they'll have (on average) lower IQs when formally tested. This is largely due to their environments. When the kids with lower IQs grow up to be adults with lower IQs, their environments are more stable, so the "heritability" of their IQ now misleadingly shows that their IQs are mostly due to genetics. It's incredibly misleading and can be wildly misinterpreted when a dipshit like Murray with no real background in intelligence research tries to read and interpret that literature.
So, yeah, that's why his implications about genetic explanations for racial IQ gaps is stupid.
Back to the registered nurse "data" that he claims exists, if we consider what I said about educational environment above, and the impact of socioeconomic status on it, this would mean that the black students who do eventually become nurses may (and I stress "may" because I'm doubtful of Murray's data claims here), on average, have slightly lower IQs as a group (I'd be very surprised if it was actually 12 points) but that would still be due to the crappy educational environments from childhood, not due to some genetic explanation. In other words, you're taking a small sample from a small group with a lower mean IQ and comparing it to a small sample from a large group with higher mean IQ. It's an unfair comparison in a lot of ways. Again, this is just on average as a group. There are lots of brilliant black kids and lots of stupid ones, just like there are lots of brilliant white and asian kids, and lots of stupid ones. (in my personal opinion, though, most kids everywhere are stupid).
Murray believes that these IQ differences are largely genetic and seems to be advocating for us to just write off these groups as permanently lower in intelligence (I infer this based on his policy suggestions in Bell Curve and his dumb comments to Tucker in the vids above). But, if we addressed/fixed the shitty economic situation of many non-White and non-Asian kids, then this gap would likely disappear and we wouldn't need to have discussions like this.
The issue (as is usually the case when people divide things by race) is actually economic, not racial, and it's certainly not genetic.