Birth order affects dating
That's become common (and accepted) Japanese wisdom. Nonetheless, it is the overarching determinant in all things from finding a compatible mate to finding a job.
With its roots in Nazi ideology, The Japan explained the origins in an article on Japanese culture, "Blood Types - Capillaries hold key to character": "It all started in 1931 in Japan.
Stereotyping by Blood Type and Birth Order The assignment of labels, be it by blood-type or position in the family, is stereotyping.
For more: Why Stereotypes Stick: Brain research explains why we believe stereotypes.
Genetics play a role as well; we know that the propensity toward shyness is genetic. Sulloway reported that only children are the "least predictable subgroup..tend to be more variable than individuals with siblings." In other words, you can't peg an only child this way or that, but most people still do.
In her study of popularity among college students, Alexandra Burt, Assistant Professor of Psychology at Michigan State University found that the most popular students turned out to be the ones with a particular form of a serotonin gene that was also associated with rule-breaking behavior. and birth order, but I'll save that for another time. The Japanese have coined a phrase, "bura-hara." It means blood type harassment.
Your blood type can influence your sex life; Japan has condom dispensing machines (see photo) with slot designations for type A, B, O, or AB buyers.
Beyond the obvious medical implications, your blood type could also be very significant in determining whom you date and how happy you are-that is if you live in Japan.