Hemoglobin A2 (α2δ2) in New World primates represents about 1/160 to 1/16 of total hemoglobin and, by virtue of this low proportion, is presumed to be functionally unimportant. Nonetheless, A2 exhibits genetic polymorphism by electrophoresis in three out of five genera, whereas the major component, hemoglobin A (α2β2), is electrophoretically invariant. Moreover, in four genera, including man, the evolutionary accumulation of mutations has been greater in δ than in β. Such findings suggest that both polymorphism and evolutionary changes can accrue to an effectively functionless and thus selectively nearly neutral gene.