东亚对血型的沉迷源自日本医生古川竹二近一个世纪前的著作，他确信个性是血型造成的。根据他的理论，每种血型都有相关的独特个性。尽管支持这些想法的实证还很缺乏，这种理论还是流行了起来。

Jill Wesson is hiring staff for her company’s new office in Taipei. She’s started going through a pile of applications, taking note of work experience, and skills in computers and foreign languages. But one bit of information keeps turning up, and she can’t make heads or tails of it.

“Why are all of these people telling me what their blood type is?” she asks. “What difference could that make? It’s an office, not a coal mine – nobody’s going to need a blood transfusion.”

East Asia’s obsession with blood types comes from the work of Furukawa Takeji, a Japanese doctor who nearly a century ago was sure that personality was caused by blood type. According to his theory, each blood type had a distinctive, corresponding personality type:

Type A people are conservative and passive, and are concerned with appearances. Although type A people are superficial and have a touch of mental instability, they are very patient and finish what they start.

Type B people get along well with others because they are straightforward, and are noted for their creativity. But type B people are also moody and become bored and annoyed easily.

Type O people are stubborn and impulsive. Their redeeming quality is that they are loyal to their friends.

Type AB people are indecisive and picky. They tend to be demanding and impatient, and they have trouble seeing things through.

Despite any real evidence to support these ideas, Takeji’s theory quickly caught on. By 1930, standard job application forms included a blank for blood type, and today market researchers use it to predict buying habits, and ordinary people use it to choose friends and romantic partners.

“I’m type O,” says Sandra, who Jill eventually hired as a receptionist, “so my boyfriend should ideally be another Type O or a Type B. Type A probably won’t match.”

And what about type AB?

“Type O with Type AB? That’s out of the question.”