Temperament theory is the only scientific theory in psychology
>https://www.booktopia.com.au/blood-type-and-personality-3-0-masayuki-kanazawa/book/9781986623810.html
>actual falsifiable "hard" scientific data produced that suggests a link between personality and blood type
That shit was literally known to Ancient Greeks. Blood transfusions were much more important than today due to constant warfare. The knowledge of blood types must have existed even if there was no chemical theory of it. Hence people could notice a correlation between blood types and psychological development.
prove me wrong, /sci/