The policy under which they might gain the right to mobility - proof of ancestral custom - fixes in place what would have been a continually evolving aspect of historical culture. The Orenda discusses a particular huron tribe picking up their whole village, including their dead, and moving it somewhere else - a practice they would repeat every few years or so. They couldn't recall any one place to say "thats where our ancestors lived" except to point at the whole territory where they made their various villages. The policy of requiring 50% native blood seems also geared towards eventually ending this allowance, given that entropy never decreases.
There is a lot to say here, but one question your comment raises is, why does the Canadian/American legal system have to acknowledge or accommodate a continually evolving aspect of historical culture? How much accommodation is fair to ask?
Many tribal practices of native peoples were and are incompatible with western legal systems. This is in part because the western legal system developed as an affirmative rejection of tribal law and customs. To take the example of England: Angles, Jutes, Saxons & Normans are all known to us; and the people are still here; but the scope of their tribal laws gradually narrowed as the framework of English law developed.
The notion of "equality before the law" gradually expanded individual rights and identity to a point where few of us recognise any tribal affiliation and led to uniquely open societies.
By that same logic, every noble house in Europe would have gone extinct by now. It's not hard, especially when you're dealing with isolated communities, to keep a lot of genetic continuity for a long time.
You don't need a 50% blood line to maintain your nobility title, you inherit the title from someone else, usually your father just like, and usually along with, a house or an estate.
To make it like aristocracy the rule should apply recursively, you are a Mohawk if 50% of your ascendants are Mohawks as defined by the same rule.
I once new a guy who was working really hard to keep a blood % out of his tribe treaty in Washington state. Said it was really hard to get his tribe to realize just how valuable it was to only have to show lineage, and not how much. The US (state?) government wanted to pay a small sum of money as due consideration for the treaty change, and he just couldn’t get the tribe to understand that the money would be gone in less than a few years, but that their grandchildren would likely have a harder time. I don’t think it helped that this guy looked pretty white, and wonder if there were people in the tribe who thought this % clause would help keep people out of the tribe who maybe didn’t look like they belonged.
