Americans--especially those of European stock--love to talk about their heritage, if they know something about it. They'll talk about where their ancestors came from and still refer to themselves as "English," "German," "Italian," etc. without quantifying their ancestry. But I've noticed an odd thing when it comes to talking about someone's Native American ancestry If you say you're Native American, one of the first questions you're likely to encounter is "how much," as in how much Indian "blood" do you possess?
This is what in Indian country is known as "blood quantum," or degree of Indian blood. Blood quantum essentially determines how far (or close) someone is to a "full-blood" Indian ancestor, and thus a "real" Indian. Whether they realize it or not, what they are really trying to determine is whether or not you are a "real" Indian. The logic is that those with more blood quantum are more authentically Native American.
What the blood quantum question fails to convey is the history behind why Indians are the only Americans required to quantify their ancestry. Blood quantum is the opposite of the "one-drop rule" which the US historically used to legally designate someone as black (meaning one drop of African blood made you black, stigmatizing and segregating people regardless of how they looked or thought of themselves culturally or racially).
Blood quantum was a tool employed by the US to separate Indians from their lands, especially during an era when Indians were thought to be the "vanishing race." To this day, it is used to limit services to Indian people. It has little--if anything--to do with a person's cultural competency or identity as a Native person. That's the reason Indian people rarely ask the question, "how much Indian blood do you have?" For more information about this very complex topic see my article "Who are Native Americans?"