As far as adoption and tartans are concerned, I see it like this. I have a decent amount of Scottish ancestry of my own on my father's side. My wife comes from a predominantly Scottish/Irish family and to honor her, I have a kilt made in the Lamont tartan. I feel that since marrying my wife all those years ago, I became part of her family, so the tartan, in a sense, becomes mine as well. Adoption could be viewed similarly. You are brought into a family that wanted you, so their familial ties become yours, regardless of your blood origins.