This Note argues that the Supreme Court’s decision in Adoptive Couple v. Baby Girl creates an apparent tension in federal Indian law. The Court’s characterization of the broader aims of the Indian Child Welfare Act of 1978 and of biology’s role within it appears irreconcilable with previous interpretations of the Act—including the Court’s own reading in Mississippi Band of Choctaw Indians v. Holyfield and that of lower courts that have adopted the existing-Indian-family exception. This Note looks to an area outside of federal Indian law—immigration law—to resolve this tension. Specifically, this Note suggests that the Court adopted the “biology plus” standard from its unwed-father cases as further developed in the context of the Immigration and Nationality Act of 1952. Reading Adoptive Couple as a continuation of the Court’s “biology plus” jurisprudence not only resolves the apparent tension, but also reveals new insights about the role of the Indian family in transmitting tribal membership in its cultural, social, and political sense.