If all smart people moved out of Africa and that's why its IQ remains so low then there would have to be tens of millions of smart Africans all over the world. Which I very much doubt. The only thing that comes to mind are Nigerians in the US and there is not so many of them there that it would affect Nigerians IQ in significant way. Also, Black immigrants to the US are pretty low educated so there is not much of a brain drain going on at all. https://i.ibb.co/Kry5rgw/obr-zok.png PNG

There could be a macro effect going on. For example, there already exists a doctor shortage in Nigeria. It could be argued crumbling health infrastructure will negatively effect socio-economic development.

https://digitalcommons.uri.edu/srhonorsprog/164/#:~:text=The%20loss%20of%20Africa's%20intellectual,the%20development%20of%20the%20continent.&text=As%20the%20most%20populated%20country,especially%20in%20the%20United%20States.

The purpose of this research is to understand the cause of the Nigerian brain-drain, the socio-economic impact, and ways to reverse the effects of the brain drain, thereby creating a brain-gain. The study is based on literary reviews and my surveys and interviews of Nigerians between the ages of 18-45, which indicates that the Nigerian brain-drain is a product of both “internal” and “external” factors working simultaneously to push Nigerians out of their country and pull them into developed nations respectively. Subsequently, skilled and educated Nigerians are attracted to the Western’s economic opportunities and what they believe to be an easy way of life. However, the brain-drain problem arises when Africans choose not to return to their native country. The data also suggests that Nigerians living abroad do not want to return back mainly due to the lack of an environment conducive for professional growth. In addition to this setback, political instability infused with corruption, and the frustration of dealing with the average Nigerian’s tolerance of corruption and greed discourages people from returning. Thus, the brain-drain continues to increase with 23,000 professionals leaving Africa annually as estimated by the World Bank report in 2007.

Same problem with the engineers who leave. Who will actually stick around to build new roads and schools, which is necessary to bring the poor rural community to the more rich and prosperous urban centers?

These are probably tests only for Botswana, this is not useful when making national comparisons. That article is pretty vague that it is almost meaningless like "gained numeracy skills", "percentage of students who can do division". wtf does that mean? Kids in other countries can do divisions too, the question is how well those kids divisions compared to each other. This is where international testing comes and Botswana is not doing very well on those.

Unfortunately, data comparing math skills is still hard to come by with these third world nations. To their credit, their government has at least succeeded in bringing literacy rate above the sub-saharan average (86% vs 64%). It seems there are other factors within their politics that is disrupting progress. For example, I found a nice article that at least tried to compare South Korea's education system with that of Botswana, and it points out many mistakes that Botswana's need to learn from. Such as: paying teachers more, addressing class overcrowding, giving schools more power over their budgets.

https://www.researchgate.net/publication/336460408_Botswana's_Education_System_A_Relative_Analysis_with_South_Korean_Education_System

It could be argued here that a low IQ nation is more likely to struggle with developing a system that's ironically, meant to improve their lives as a whole. Which I believe is true. And to make matters worse again, the Africans who could have been part of these boardroom meetings aimed at fixing these problems, would rather get the same job but in another high paying country instead. So it's a cycle of putting incompetent people in charge, who make systematic mistakes that doom the next generation, who are either forced to go through a failed learning system, or the ones who do pass with flying colors, quickly abandon the country for the next best thing.

I wouldn't dwell to much on those numbers. Polish IQ certainly didn't go down one standard deviation within 10 years. These are mostly measurement errors.

So what do you propose happened to Europe in the last 100 years? Was IQ always on the rise, as it should be. Because industrialization and the flynn effect have been linked to increasing IQ scores? Or did the Soviet/Eastern Bloc countries have deleterious effects on their population, as a result of food shortages and state sponsored fear?

I picked Taiwan and Hong Kong because they are both >90% Han Chinese, not because they are neighboring countries. That's why I called them mini Chinas

If you use ethnicities, doesn't this throw out the entire principle of grabbing IQ scores from neighboring nations? Israel borders many Arab nations but they are regarded as different people. Cuba, Jamaica, Dominican Republic & Haiti are all distinct from one another despite being Caribbean islands. Brazil differs a lot from the rest of South America for being one of the few non-Spanish colonized countries. And Africa has several distinct ethnic groups, it would be unfair to say the San People of South Africa are somehow directly related to the Ethiopians in the far North, or the Bantus in the West part of the continent.

And while I agree with you that yes, China, Hong Kong, Taiwan are indeed related by blood, it's still unfair to copy and paste statistical information from one another. This was used in the North Korea/South Korea comparison. Not only do they have different governments and economic success, but biologically speaking, North Koreans are suffering by growing up shorter than their South Korean cousins (again, most likely a result of the massive famines they had in the 1990s).

https://www.bbc.com/news/world-asia-41228181

In Chinese history, we do know Mao and the Communist government had equally starved off millions of their own people, while Hong Kong and Taiwan were fortunate enough to have not been sewn at the hip to experience that regime.