But why expect differential brain drain between Africa and Asia
Here is a throwaway guess: because Asia is rapidly developing and Africa is not. If you’re very smart and in (ex-Japan) Asia, you can stay and be successful (make millions / cure cancer / become a pop star / etc.) locally. It’s a fluid growing environment. But if you’re in Africa, your chances of local success are much smaller and, correspondingly, your incentives to emigrate are much higher.
Here is a throwaway guess: because Asia is rapidly developing and Africa is not. If you’re very smart and in (ex-Japan) Asia, you can stay and be successful (make millions / cure cancer / become a pop star / etc.) locally. It’s a fluid growing environment. But if you’re in Africa, your chances of local success are much smaller and, correspondingly, your incentives to emigrate are much higher.