There’s an Ancestry ad where a man trades his lederhosen for a kilt. And another where a woman traces her ancestry to the matriarchal Akan people of Ghana to conclude, “When I found you in my DNA, I learned where my strength comes from.” And yet another where a man bonds with his Irish neighbor after finding out his own DNA is 15 percent Irish. But marketing campaigns for genetic-ancestry tests also tap into the idea that DNA is deterministic, that genetic differences are meaningful. They trade in the prestige of genomic science, making DNA out to be far more important in our cultural identities than it is, in order to sell more stuff.