In Japan, blood type is used to determine one’s personality and temperament. Like astrology, the scientific community often dismisses blood type as an indicator of personality, but that doesn’t stop its popularity in Japanese women’s magazines, where blood type horoscopes are published.

In Japanese video games, blood type is commonly a dimension in character creation. In fact, some Japanese might even be shocked if a foreigner didn’t know her blood type.

The history of the theory that blood type determines personality is actually a dark one. In 1900, Austrian scientist Karl Landsteiner discovered the four blood types. Like 19th-century scientists who used brain size (the larger the brain, the more advanced) to propagate theories of racial and gender superiority, many (white) scientists used the blood type theory as a way to push forward their own ideas of racial supremacy. Scientists from the west suggested (falsely, obviously) that Asians were inferior and sub-human since the vast majority of them—like animals—had type B blood. In 1927, Takeji Furukawa, a Japanese professor, introduced the theory to the Japanese public in a paper entitled, “The Study of Temperament Through Blood Type.” Even though he lacked the proper credentials and backed up nothing scientifically, the public embraced the idea of blood type as a determination of personality. The Japanese government even commissioned a study to determine if they could breed better soldiers. In the 1970s, a book by Masahiko Nomi revived the idea, which is still popular with the general Japanese public. In 2008, four books on the topic have hit Japan’s top ten bestseller lists.

Find Out Your Blood Type

One of the easiest ways to find out your blood type is to give blood. Since it has to be matched for donation, they type it anyway, so you can always ask. If you’re pregnant, doctors administer certain blood tests to assess potential genetic problems, so determining the mother’s blood type is standard. You can ask your doctor to perform a test when you get blood drawn, but since it isn’t usually medically relevant, you may have to pay for the test. The easiest way? Ask your parents; they probably know.

What Your Blood Type Says About Your Personality

Type O
You are the social butterflies. Often popular and self-confident, you are very creative and always seem to be the center of attention. You make a good impression on people and you’re often quite attractive. Organized and determined, your stubbornness will help you reach your goals. You make good leaders. Lovewise, O is most compatible with O and AB. Common career choices: banker, politician, gambler, minister, investment broker, and pro athlete.

Type A
Type As may seem calm on the outside, but inside, you’re filled with anxiety and worry. You’re perfectionists and often shy and sensitive. Usually introverted, you’re stable and thoughtful. You make good listeners and are sensitive to color and your surroundings. You like to be fashionable and are up on the latest trends, but never flashy or gaudy. You like romantic settings and often shun reality for fantasy worlds. A is most compatible with A and AB in the love department. Common career choices: accountant, librarian, economist, writer, computer programmer, and gossip columnist.

Type B
You can be very goal-oriented and often complete the ambitious tasks set before you. Outgoing and very charming, you’re good at reading people and providing support. Though critical of appearance (but not your own), you aren’t picky and are unlikely to dwell over the little things. Type Bs are impulsive individualists who often create their own path in life. You are very strong and optimistic. B is most compatible with B and AB lovers. Common career choices: cook, hairdresser, military leader, talk show host, and journalist.

Type AB
Not surprisingly, ABs can be quite dualistic, possessing both A and B traits. You may be shy and outgoing, and hesitant and confident. You often stand out from others, don’t like labels, and are nice and easy going. You are logical and determined to do things correctly. Usually trustworthy, you like to help others. You often speak in a serious manner. Your patience, concentration, and intelligence are admirable. AB can find a soul mate with any other blood type. Common career choices: bartender, lawyer, teacher, sales representative, and social worker.

We all love to know things about ourselves and blood type is just another fun way to learn new traits and understand why we do certain things. You don’t have to believe in it to get something out of it—just have fun with it and take it with a grain of salt.