ABO blood group system and likely predates human migration from Africa. The O01 allele is considered to predate the O02 allele. Some evolutionary biologists theorize that there are four main lineages of the ABO gene and that mutations creating type O have occurred at least three times in humans. From oldest to youngest, these lineages comprise the following alleles: "A101/A201/O09", "B101", "O02" and "O01". The continued presence of the O alleles is hypothesized to be the result of balancing selection. Both theories contradict the previously held theory that type O blood evolved first. It is possible that food and environmental antigens (bacterial, viral, or
Blood type personality theory 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. Some researchers believe blood types are associated with personality traits. Many medical surveys have been conducted, such as those for hormone secretion traits (DBH, COMT, MAO etc.), or the blood-type antigens in neurons, or the antigens expressed on surfaces