Genetic parentage is the predominant theory of parentage. The US Constitution protects genetic parents’ opportunity to parent, and states often treat genetics as sufficient for parentage, at least for child support. No moral principles justify the latter inference. Nor can genetic ties directly justify parental liberties. Consequentialists imagine that family law exploits evolutionary incentives to serve child welfare, but genetics is too crude a proxy for child-rearing quality. Genetic parentage rules poorly realize perfectionist or natural law visions of the procreative family. This purpose is illegitimate. No adult can have a fundamental right to control a child’s life because it serves the adult’s ends. Nevertheless, many reasonable citizens value genetic heritage. They should be free to pursue their vision of a valuable family if consistent with equal respect for the child and other adults. Citizens cannot legitimately object if the law prevents them from using others’ genetic code to create a child to raise themselves. The child has no legitimate objection if the community ensures their genetic parents fulfill the parental role promptly and adequately. Helping families provide adequate care offset the parentage lottery. As constitutional law recognizes, adults have a derived liberty right to raise their genetic children.

Parentage doctrines have proliferated, yet procedures to resolve the inevitable conflicts are lacking. Some states have priority rules, but the rankings are partial and rest on shallow reasoning. Recent trends favor the best interest of the child test, but it empowers judges to assess the pertinent values anew in each case. This chapter reconstructs American parentage law into a system of ordered rules to resolve parentage disputes with minimal ad hoc decision-making. Parentage law begins with the biological parent’s conditional liberty, reflected in the gestational presumption and the genetic petition or acknowledgment. Biological parents can also waive their childrearing liberty or forfeit it by not promptly and adequately raising the child. If there is only one legal or presumed parent, their parenting project can be shared with a partner through a second-parent adoption, acknowledgment of parentage, or preconception agreement. The parent may also seek caregiving help without sharing parenthood, but risks forfeiting their power to revoke this caregiving privilege if they share responsibility long enough for child and caregiver to develop rights and duties. The marital and residential presumptions are evidentiary inferences to the same biological, agreement, forfeiture, and caregiving grounds, so should be rebuttable only on the same basis.

Modern law allows some adults to agree among themselves on allocating parenthood through adoption, preconception agreements, surrogacy, and voluntary acknowledgments. These doctrines cannot be justified by the adults’ intentions, promises, contracts, or similar social conventions. Those powers rest on agents’ authority over their own lives; no one can have a personal right to decide who will control a child’s life. However, liberal justice requires such legal authority. Many reasonable citizens value childrearing irrespective of biological ties and should have a derived liberty to pursue families. Excluding citizens from parenthood denies them fair equality of opportunity. Modern parentage agreements empower nonbiological parents to build families in ways that respect themselves, the child, and other parents. Adoption empowers an adult to create parenthood through an express commitment, subject to state oversight to protect the child and existing parents. Second-parent adoption and acknowledgments of parentage enable a single parent and their partner to agree to share parenthood prospectively, which prevents subordination in familial projects, protects the child’s relationships, and facilitates equality for lesbian and gay adults. Preconception agreements do likewise for a gestational parent and their partners. Well-designed regulations may render gestational surrogacy consistent with equal respect for the surrogate and women generally.

This chapter explores the approach of the CJEU and the ECtHR to the highly contentious topic of surrogacy in order to unravel the understanding of motherhood endorsed by these two European courts. It shows that legal motherhood continues to be tied to gestation and birth, thus placing intended mothers in a precarious legal position, especially compared to intended (genetic) fathers. As part of its effort to explain this gender imbalance, the chapter uses the experience of surrogacy as a window for a broader discussion on the gender of legal fictions governing the attribution of parenthood. Whilst the rule mater semper certa est remains one of the most immutable facts of European family laws, legal systems have generally demonstrated a certain flexibility and attention to context in determining legal fatherhood, at times departing from the marital presumption. The chapter argues that this differential attitude reflects a long-standing socio-legal resistance to breaking the continuum gestation-motherhood-caregiving, and aligns with the gendered and higher expectations that legal systems place on mothers compared to fathers.