The blood type personality theory is a pseudoscientific belief prevalent in Japan which states that a person's blood group system is predictive of a person's personality, temperament, and compatibility with others. The theory is generally considered a superstition by the scientific community.
One of the reasons Japan developed the blood type personality indicator theory was in reaction to a claim from German scientist Emil von Dungern, that Blood type B people were inferior. The popular belief originates with publications by Masahiko Nomi in the 1970s.
Although some medical hypotheses have been proposed in support of blood type personality theory, the scientific community generally dismisses blood type personality theories as superstition or pseudoscience because of lack of evidence or testable criteria. Although research into the causal link between blood type and personality is limited, the majority of modern studies do not demonstrate any statistically significant association between the two. Some studies suggest that there is a statistically significant relationship between blood type and personality, although it is unclear if this is simply due to a self-fulfilling prophecy.
Overview
According to popular belief, people with type A blood are friendly and kind, people with type B are spontaneous and creative, and people with type O are confident and aggressive. In a logical extension of this system, those with type AB are a mix of stereotypical A and B traits.
History
The idea that personality traits were inherited through the blood dates as far back as Aristotle. Hippocrates also sought to link personality biologically, linking traits with the four bodily humors – sanguine, phlegmatic, choleric, and melancholic.
In 1926, Rin Hirano and Tomita Yashima published the article "Blood Type Biological Related" in the Army Medical Journal.
Takeji Furukawa
In 1927, Takeji Furukawa, a professor at Tokyo Women's Teacher's School, published his paper "The Study of Temperament Through Blood Type" in the scholarly journal Psychological Research. The idea quickly took off with the Japanese public despite Furukawa's lack of credentials, and the militarist government of the time commissioned a study aimed at breeding ideal soldiers. The study used ten to twenty people for the investigation, thereby failing to meet the statistical requirements for generalizing the results to the wider population.
On the other hand, in 1934, Fisher announced the chi-squared test, which is very popular at present, for the first time. Several scholars said that they found statistically significant differences in analyzing Japanese work conducted at that time.
In another study, Furukawa compared the distribution of blood types among two ethnic groups: the Formosans in Taiwan and the Ainu of Hokkaidō. His motivation for the study appears to have come from a political incident: After the Japanese occupation of Taiwan following Japan's invasion of China in 1895, the inhabitants tenaciously resisted their occupiers. Insurgencies in 1930 and 1931 resulted in the deaths of hundreds of Japanese settlers.
The purpose of Furukawa's studies was to "penetrate the essence of the racial traits of the Taiwanese, who recently revolted and behaved so cruelly." Based on a finding that 41.2% of Taiwanese samples had type O blood, Furukawa assumed that the Taiwanese rebelliousness was genetic. His reasoning was supported by the fact that among the Ainu, whose temperament was characterized as submissive, only 23.8% is type O. In conclusion, Furukawa suggested that the Japanese should increase intermarriage with the Taiwanese to reduce the number of Taiwanese with type O blood.
Masahiko Nomi
Interest in the theory was revived in the 1970s with a book by Masahiko Nomi, a journalist with no medical background (he graduated from the engineering department of the University of Tokyo). Few Japanese psychologists criticized him at that time, so he continued to demonstrate statistically significant data in various fields and published several books with these results. Later after his death in 1981, Masahiko Nomi's work was said to be largely uncontrolled and anecdotal, and the methodology of his conclusions was unclear. Because of this, he was heavily criticized by the Japanese psychological community, although his books remain popular. His son, Toshitaka Nomi, continued to promote the theory with a series of books and by running the Institute of Blood Type Humanics. He later established the Human Science ABO Center for further research and publication in 2004.