We’re not going to find new strange deficiencies. However we might well find perfectly straightforward deficiencies that didn’t used to be deficiencies if for example people’s diet changed dramatically and the consumption of some fundamental component of brain development i.e. iodine, dramatically declined with that dietary change e.g. a dramatic decline in iodine rich dairy consumption among people of north European descent if it wasn’t compensated for in some way like with the addition of iodine to salt.If correct then as Germany started the process of adding iodine to salt in 1981 there will be a cohort of Germans in their 20s coming through now so we should find out soon enough if there’s been an effect.A point worth considering for Germans is they changed their education system after their low results when PISA first started. If the iodine idea is correct then they may have made a mistake.
Actually we might find strange new factors in underlying IQ differences if the basic idea was accepted and focus and research shifted to groups who *ought* to have the same average IQ (because genetically very similar, very close geographically etc) but for some reason they don’t.