Is membership to a Native American tribe contingent on ancestry or past membership?

You can be indigenous to Canada or mexico and still have the same dna results as a native american. DNA is a non-native look on what makes a person "native" (although it is becoming a useful tool in distinguishing who is part of a tribe and who is not, but not for the reasons the U.S. government wants it to be) anyways...if you dont have any connection to a particular tribe, why would you want to join any of them? If you arent raised in the culture, it isn't yours to claim...