The term “sexual complementarity” is thrown around a lot in debates on marriage and sexuality, but it seems to be explained rarely. Thus, misunderstandings abound as to what “sexual complementarity” refers. Is it about anatomical complementarity? About just hormones or personalities complementing one another?
Here are a few things to keep in mind when you hear the term “sexual complementarity”:
Sexual complementarity does not mean merely psychological or behavioral complementarity (i.e., what a compatibility test or personality assessment evaluates), nor does it mean merely physical complementarity (i.e. having the right “parts” that fit together).
Sexual complementarity refers to something deeper. It certainly is biological (i.e. psychological and physical), but at its root it has a more personal component.
This personal component refers to that part of you that is the heart of your personal identity—what makes you, you. This “personhood” that each individual human being has is something more than merely the material stuff of your body. This is obvious because if your identity was simply dependent on the material stuff that composes your body, you wouldn’t be the same ‘you’ for very long; the actual atomic material of your body is not the same stuff throughout your whole life (just think of the hair and skin you shed and grow).
No, your personal identity is an immaterial principle of continuity—this is why you can be responsible for something you did in the past or why you can plan to do something in the future and then actually do it.
A person is not merely a body, but a person is not merely a spirit, either.
Our bodies are not machines. Our bodies are physical manifestations and expressions of the immaterial aspects of ourselves. Personhood encompasses both the immaterial (mind) and the material (body). Who you are as a person necessarily includes not only your mind but your very genetic and physical makeup. This means that every man or woman is a man or woman in the very core of his or her identity. It is an essential aspect of who he or she is and what he or she does—such as being in relationship with others.
Manifesting our maleness and femaleness
Sex (maleness or femaleness) is deeper than having certain body parts. If a man loses a certain part of himself because of an accident, he remains a man. Nonetheless, one key way that sex (maleness or femaleness) is manifested is physically—in the body.
We know that there are two kinds of human beings: man and woman. Sure, each individual might differ in their combination of masculine or feminine traits physically or psychologically, but that doesn’t make any man less male or woman less female. Those traits are just particular details about one’s maleness, for a man, and femaleness, for a woman. Biologically, man and woman fit together in a way that can result in the creation of new human beings. This “fit” is not only biological (psycho-physical). With sexual complementarity, the “fit” is even more so at the level of their personhood.
An embodiment of these universal principles
This is not to say that men or women aren’t compatible with members of their own sex. On the contrary, we have relationships with members of our own sex that are often strong, deep, committed, and loving. Nonetheless, by their nature, these relationships are not marriage. They are not necessarily better or worse than marriage; they are just different.
Only man and woman can engage in sexual intercourse (properly speaking), which is the physical expression of inward, unique reality about their personhood. Man and woman together are a microcosm of broader humanity in a way that no relationship exclusively male or female is ever able to be.
Man and woman together exemplify the actual embodiment of the universal principles of masculine and feminine. A single-sex relationship simply cannot have this embodiment. A man’s and a woman’s bodies—who they are as persons—come together each as male or female, and so by its very nature the union between a man and woman is unlike any other relationship.