This is a matter of one's priors. One could just as easily say that it's one thing to find a clearly environmentally mediated difference in some extreme situati

This is a matter of one's priors. One could just as easily say that it's one thing to find a clearly environmentally mediated difference in some extreme situation (i.e. between North and South Koreans), another to pretend that such differences are enough to explain even a worthwhile fraction of the achievement gap – especially between different ancestries within the same polity, in the absence of any overt discrimination or substantial evidence for covert one. It'd be a better argument, even. Despite severe global sanctions and a ridiculous political and economic system, there isn't that much of a difference between North and South Koreans. Denizens of DPRK still maintain an orderly society with universal literacy and advanced domestic technology, and overall demonstrate cognitive performance on at least European level – with like 5% of GPP per capita that South Koreans have, on par with poor African states. Which are, indeed, among the lowest-developed, and frequently fail to maintain basic infrastructure – despite external support. I do note that you have ignored my meta-level question, though, and that says enough.