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 diet Blood type diet The blood type diets are fad diets advocated by several authors, the most prominent of whom is Peter J. D'Adamo. These diets are based on the notion that blood type, according to the ABO blood group system, is the most important factor in determining a healthy diet, and each author recommends a distinct diet for each blood type. The consensus among dietitians, physicians, and scientists is that these diets are unsupported by scientific evidence. In what was apparently the first study testing whether there was any benefit to eating the "right" diet according to one's blood type,