You take it as a given that the intelligence of Ashkenazi Jews relative to other populations is down to genetics, but there are equally compelling cultural explanations for this. As for the lipid metabolism hypothesis, I have thus far found no studies which confirm such a correlation, and in the early 20th century, tests showed Ashkenazi Jews underperforming on IQ tests relative to other European populations (see: Hirsch, N. D. M. (1926). A study of natio-racial mental differences. Genetic Psychology Monographs, 1, 233-406.), so what changed?
I think the level of intelligence that humans are capable of attaining is far more malleable than you are choosing to admit. Culture, education, and conditions during fetal and childhood development are all potentially significant contributory factors.
As environmental conditions decrease in influence (like in the West, where people are generally extremely well fed and there are things like iodine and folic acid supplements to prevent neural defects, among other prenatal care advances), inbuilt genetic differences become more pronounced. This is why a trait like height or IQ would appear to have an extremely low heritability in, for example, subsaharan Africa during a massive famine, versus a high heritability in the US today because we don't have such extremes in environmental conditions. Research support that IQ is polygenic and highly heritable, see
this
As for the education factor specifically, we know that IQ predicts educational success, not the other way around.
This study looked at g-scores and GCSE scores 5 years later for 70k students and found that g predicted ~70% of the variance in test scores.
This highly well-researched article (love Gwern) shows that high childhood IQ scores doesn't predict success that well because they regress to the mean. You could also phrase this as saying that high childhood education isn't very significant in maintaining base-level genetic IQ. All the students were first selected for a high IQ, before they were put into the educational training facility.
If you want an example of some genes that affect IQ, there's
this research paper, which also argues that IQ differences are due to recent polygenic selections. Here's some of the SNPs and genes they list:
NPTN gene
possibly rs324650
APOE
We also know that mutations can massively increase IQ; see
here, also published
here
There's an example of a scottish family with an extremely rare mutation that increases verbal IQ by ~25 points in those with it, but also makes them go blind in their 20s. The control is family members without it, which is easy to see (pun intended), so its confidently the only gene causing the increase. I can't find the actual study, but I can keep looking if you want more evidence?
For your point about Ashkenazi's, first, I'm not reading a book, give me a shorter summary somewhere. But a simple counterclaim is that they could have suffered from poorer nutrition (not integrating into social structures→environmental factors the other groups were developing).
Secondly, here's a summary from
this research paper on the selection for IQ within Ashkenazi jews:
"Today's Ashkenazi Jews suffer from a number of congenital diseases and mutations at higher rates than most other ethnic groups; these include Tay–Sachs disease, Gaucher's disease, Bloom's syndrome, and Fanconi anemia, and mutations at BRCA1 and BRCA2. These mutations' effects cluster in only a few metabolic pathways, suggesting that they arise from selective pressure rather than genetic drift. One cluster of these diseases affects sphingolipid storage, a secondary effect of which is increased growth of axons and dendrites. At least one of the diseases in this cluster, torsion dystonia, has been found to correlate with high IQ. Another cluster disrupts DNA repair, an extremely dangerous sort of mutation which is lethal in homozygotes. The authors speculate that these mutations give a cognitive benefit to heterozygotes by reducing inhibitions to neural growth, a benefit that would not outweigh its high costs except in an environment where it was strongly rewarded."
edit: i was writing this in paragraphs and forgot to finish thoughts