There are a number of ways in which we might identify a child’s parents. For mothers, these are currently: (1) giving birth; (2) contributing the egg; and (3) intending to raise the child. For fathers, they are: (1) contributing the sperm; (2) intending to raise the child; (3) being married to the child’s mother; and (4) being registered on the child’s birth certificate.[192] Almost all mothers satisfy all three criteria, and many — although by no means all — fathers will fulfil all four. Where each of the three defining features of motherhood vest in one woman, and all four defining features of fatherhood vest in one man, we have an example of the paradigm case, in which the parenthood of a child is entirely straightforward. Of course, that child might subsequently be adopted, which would result in the separation of, inter alia, the intention to raise the child and genetic relatedness. Given the availability of legal adoption, even within the paradigm case, legal parenthood is necessarily potentially impermanent.
Nevertheless, where a man and a woman conceive a child sexually, within marriage, whom they intend to raise, we can unproblematically accept that they are that child’s parents. Some parents who differ only marginally from this paradigm case will also very obviously be a child’s parents. An unmarried father, for example, who is registered on the birth certificate, genetically related to his child and intends to raise her is unquestionably that child’s father.
But what if we move slightly further away from the paradigm case. What if, for example, a child is conceived using donated sperm? Here, we might have a man who intends to raise the child; is married to the child’s mother; and is registered on the birth certificate, and another man whose sperm was used to fertilise the mother’s egg. Who is the ‘father’ of this child? Following a surrogacy arrangement, we will have a woman who intends to raise the child and who may have contributed the egg, and another woman who gestated the pregnancy and gave birth. Which woman is this child’s mother? Because the principle of parental exclusivity insists that one mother and one father must be singled out, the conventional approach to answering these questions has been to try to work out which of the features that we normally associate with parenthood should be decisive. While this might be relatively straightforward if a universally applicable hierarchy could be devised through which one factor — such as the genetic link — always took priority, as we see in the next sections, the law has instead used different tests in different circumstances, resulting in an extraordinarily incoherent approach to the identification of parents.