You could say that five hundred years ago was the basis of blood quantum in Ibero @-@ America . But in Anglo @-@ America , while it was some preoccupation with it , it was not formalized until the passage of the General Allotment Act , mid @-@ 1880s . At that point they began to define Indian as being someone who was demonstrably and documentably of at least one @-@ quarter by quantum blood indigenous in a given group . You couldn 't be an eighth Cheyenne and an eighth Arapaho and be an Indian . You had to be a quarter Cheyenne or a quarter Arapaho or hopefully a quarter and a quarter . The reason for this was quite clear . They were identifying Indians for purposes of allotting them individual parcels of land in the existing reservation base at that point . If they ran out of Indians identifiable as such , then the rest of the land would be declared surplus . So it was clearly in the interests of the government to create a definition of Indianness that would minimize the number of Indians that were available . It was an economic motivation for the application of this genetic criteria to Indianness in the first place . It 's become increasingly so ever since . " ( David Barsamian ( December 1995 ) . " Interview with Ward Churchill : Historical and Current Perspectives " . Z Magazine . )