No, it's not. In fact, both results of studies showing such differences and the factors likely producing them are frequent matters of discussion on the left.
> It’s also axiomatic on the left that all cultures are equally effective at raising successful, healthy children.
Also not true, though the left (unlike the right) is unlikely to limit it's consideration of “culture” to a narrow set of values that parents of certain ethnic backgrounds are presumed to have or not have, and consider the sources of culture influences much more broadly than the right does.
> The German study suggests that culture matters,
It is quite consistent with the idea that physical and broad social context matters, and that broad aspects of the physical context to which various groups are selectively subjected, as well as elements of the broad US social context, are particularly harmful to and preserve the disadvantage of various historically disadvantaged groups is actually more widely accepted as established fact on the left than the things you mislabel as axiomatic.
That's because it's an irrelevant classification.
> It’s also axiomatic on the left that all cultures are equally effective at raising successful, healthy children. The German study suggests that culture matters, which counters this axiom.
Assume you would do these tests on Irish Americans in the mid-1900s, or Italian Americans in the late 1900s, and compare to other groupings of people. Assuming similar results:
Would you say the results say anything about Irish or Italian blood or Irish or Italian culture being less intelligent?
Or would you say that the results could be rooted in something closer to economic standing or housing area or a number of other factors?
https://en.wikipedia.org/wiki/Ashkenazi_Jewish_intelligence
However, even the above can just be used to maintain the tinfoil conspiracy theory about jews running the world. So.... you cant get any useful conclusion with this data, even if you use the data as it is (i.e. to say "on average", and never use it to guess a certain person's intelligence based on ethnicity).
Also, the genes responsible for skin color,afaik, has nothing to do with the intelligence of that human. Otherwise, there would literally be a cap on iq for whiter or darker skinned humans. But there is not, any ethnicity can produce stupid individuals and geniuses as well.
It’s also axiomatic on the left that all cultures are equally effective at raising successful, healthy children. The German study suggests that culture matters, which counters this axiom.