Theory of Jews and Japanese
Jews: only people adapted to McVeigh posture. Jewish population flatlined and declined immediately after writing became common (700 BC). Before then, it had been growing fast. And it was, unlike Greek writing, a very shoulder dominant form of writing. In 600 BC, Judah had by far the highest literacy rate in the world, higher than Greece would have during the golden age (the content of that writing, though, leans heavily toward the McVeighan). The Documentary Hypothesis, which seems true, would also only make sense if Jewish compositional methods were precisely the opposite of Greek ones, which does make sense due to the vastly greater shoulder dominance in writing. Jewish fertility since has been largely a product of writing direction. They make the most fearsome keyboard warriors. Ask Yud.
Japanese: Basically ancient Greeks/Spanish/Florentines in every way before 1870. Then we see something interesting. A sort of inverse bicam becomes dominant. The fertility rate skyrockets, militarism and cruelty (Dirlewanger was clearly bicam) rises. But the core commandments of classical bicam: obey your superiors and pick your battles- are completely flipped on their head. And after 1945 we rapidly transition to flatback. So we go from honorary Greeks to honorary Aryans to honorary secular Jews in the span of a century. Crazy.
As to why this didn't happen in Southern Europe? Writing direction. Without a doubt.