That mother had a mother.

That grandmother had a mother, and so on back through time.

The seventeen volunteers each have a similar chain of maternal ancestors extending back through time.

Somewhere in those chains, there is a common ancestor — a woman from whom all seventeen volunteers and Kwäday Dän Ts’ìnchi descend through their maternal lines.

That common maternal ancestor might have lived before Kwäday Dän Ts’ìnchi — his ancestral grandmother, or great-grandmother, who was also the ancestral grandmother of the volunteers’ maternal lines.

Or the common ancestor might have been Kwäday Dän Ts’ìnchi’s own mother, if any of his sisters — women who shared his mother and therefore his mitochondrial sequence — had surviving maternal-line descendants among the volunteers.