Over the past three decades rates of divorce, single parenting, and cohabitation have risen precipitously. Nontraditional families (which diverge from "a middle-class family with a bread-winning father and a stay-at-home mother, married to each other and raising their biological children") constitute the majority of families in the United States today. Shared Earning/Shared Parenting Marriage (also known as Peer Marriage) where two heterosexual parents are both providers of resources and nurturers to children has become popular. Modern families may also have single-parent headed families caused by divorce, separation or death, families who have two parents who are not married but have children, or families with same-sex parents. With artificial insemination, surrogate mothers, and adoption, families do not have to be formed by the heteronormative biological union of a male and a female.