Nonoko Kamai
Nagoya, Japan

Why do Japanese people believe in a relationship between blood type and personality? Beginning in the 1970s, the blood type personality hypothesis became fashionable in Japan and it is still popular today.⁵ A women’s magazine focusing on the topic once sold seven billion copies and there are still fortune telling books based on blood types.⁵

Even though the research about blood type and personality is now dated, many Japanese people still believe in it. The idea was first suggested by Hara and Kobayashi in 1916 in a paper postulating that even brothers could exhibit differences in personality, grades, and physical characteristics, and that these were correlated with their ABO blood groups.⁴ Next, Furukawa published a thesis about a relationship between ABO blood groups and patterns of human behavior in 1927.⁴ He hypothesized that people with Type A blood were more gentle, shy, and worried more, while those with Type B blood were kinder and more cheerful.⁴ In 1971, Nomi published the book Ketsuekigata de wakaru: Aisho (Understanding your love compatibility through blood type) that used Furukawa’s 1927 hypothesis to argue that compatibility in relationships depended on blood type.⁴ He further explained that a person’s blood type may be identified by examining body parts such as hair, teeth, and organs.⁴ In 1983, many books about blood type personality theory were published, and this became a social phenomenon.³

There are three main reasons why many Japanese people believe in this hypothesis. It is culturally popular to categorize people by stereotypes. We tend to collect examples that match a stereotype, and those examples confirm our beliefs.³ This may also be explained by the Barnum effect, a psychological effect defined by Lexico as “the tendency to accept as true types of information such as character assessments or horoscopes, even when the information is so vague as to be worthless.”¹ Another reason is that Japan previously did not have anything to classify personalities, such as astrology in western countries, until the advent of blood type hypothesis.⁶ According to Kubo and Miyake, 60% of Japanese people believe in this hypothesis. After 2004, the number of television programs and books about the relationship between blood type and character increased yet again.³

Some researchers in Japan have stated publicly that there is no relationship between blood type and personality. Kubo and Miyake carried out an experiment using the “Big Five” personality traits described by Goldberg and Sancier.³ According to the American Psychological Association, this is a model of the “primary dimensions of individual differences in personality. The dimensions are usually labelled extraversion, neuroticism, agreeableness, conscientiousness, and openness to experience, though the labels vary somewhat among researchers.”² They conducted their experiment on 298 university students (male: 167, female: 130, not sure: 1) who filled out a questionnaire about their personality and blood type.³ The results indicated that the five dimensions of personality did not correlate with blood type.³ These results have been corroborated by other experiments.

While these studies disproved the hypothesis through psychological testing, biology also does not support it. Since ABO blood types are classified by the glycoprotein present on the surface of red blood cells, people who have Type O blood and have no glycoprotein marker would also not have any evidence to define their personality.⁴ The gene that codes for ABO blood type is located on chromosome 9.  If the blood type personality hypothesis were true, there should also be similar DNA evidence for personality and physical constitution.⁴ However, this evidence does not exist.

Although this hypothesis is not supported by modern science, Japanese people continue to believe in it. But what effect might this have on our perception of ourselves and others? We need to continue to educate people that this relationship is just a hypothesis and is not supported by science.

References

1. Barnum effect. In: lexico.com. Accessed December 8, 2019.
2. Big Five personality model. In: American Psychological Association. apa.org. Accessed December 8, 2019.
3. Kubo Y, Miyake Y. Ketsuekigata to seikaku no kanren nituiteno chosatekikenkyu.　(Correlation between blood types and personalities). Takahashi, JP: Kibi International University; 2011:93-100.
4. Saito M. Zinruigaku yorimitaru ketsuekigata to seikaku. (The blood type and character consideration in anthropology). Nisshin, JP: Nagoya University of Arts and Sciences; 2005:65-78.
5. Sato T, Watanabe Y. Gendai no ketsuekigata seikakusindan boom to sono sinriteki kenkyu. (Psychological studies on blood-typing in Japan). Psychological criticism. 1992;35(2):234-268. doi:10.24602/sjpr.35.2 234
6. Sugiyama S. Zikogainen ni oyobosu ketsuekigata stereotype no eikyo oyobi barnum effect no kento (The effects of “blood type stereotype” on self-concept). Hachinohe, JP: Hachinohe Gakuin University; 2005:47-57.