This essay responds to Professor Courtney Joslin’s treatment of marriage-equality opponents’ “responsible procreation” argument in her article, "Marriage, Biology, and Federal Benefits". Joslin addresses the argument’s central premise, which she labels “biological primacy” — the notion, “that the government’s historic interest in supporting marriage and marital couples is to isolate and specially support families with biologically related children.” Through a historical account of the extension of federal benefits to biologically unrelated children, Joslin exposes that premise as myth, rather than reality. In this response, I use Joslin’s historical analysis as a window into biological primacy’s normative stakes and supplement her compelling historical case with a normative claim. While my analysis applies in significant ways to biological primacy writ large, I specifically target what Joslin terms the “biological preferentialism” claim, which suggests, “that the government can limit benefits to families with biological children because these families are simply superior.” I argue that while this claim is viewed as a natural outgrowth of the responsible procreation argument, it is in fact rooted in an extant argument for dual-gender parenting. Biological preferentialism repackages an otherwise outmoded argument in seemingly neutral and innocuous terms. By using biological parenting as code for male–female parenting, the argument cleverly conceals and yet invariably rests on traditional gender scripts associated with marriage and the family. Biological preferentialism, in other words, functions as a way to neutralize yet preserve positive and normative arguments about sex roles — arguments that have been rejected in both family law and constitutional law.