Most people seem to be confused how blood types and personality traits connect. They dismiss it as Japanese pseudoscience not understanding the origins. The truth is that the origin of the theory wasn’t even born in Japan. German internist Baron Emil von Dunger, together with Ludwik Hirszfeld discovered the heritability of ABO blood groups in 1911. He later claimed that blood type A, more common in Europe was superior to blood type B, more common in Asia. That kicked off an obsession on the part of Japanese professor Takej Furukawa claiming the exact opposite. Here is more: