Everyone has two parents, four grandparents, eight great-grandparents — the arithmetic runs away from us within a few generations. No society treats every one of those people as equally its own. A descent rule is the filter each society applies: a socially agreed instruction for which of your ancestors count, and therefore which living people are your group. The chart on the left never changes. Flip the rule and watch the same twenty-two people sort themselves into members, outsiders and in-laws — and notice, on the way, that your own children are not always on your side of the line.
One chart, five rules
Whose people are you?choose a descent rule to begin