Most theories of parentage fail to explain the genesis of the right to parent—for example, why does a biological relationship generate parental rights? This Article shows that the law of parental rights mirrors theories of acquiring property, and that the law has shifted over time, from favoring a property right based in genetics to a Lockean theory of property rights earned through labor. The growth of Lockean labor-based theories is epitomized in reforms to parentage laws that incorporate functional theories of parenting, meaning that adults who perform caretaking work that creates a significant relationship with children are recognized as legal parents, even if they are not genetically related to the child. A labor-based understanding of...