“Two-in-One-Flesh” Is More Than a Metaphor

The phrase “two-in-one-flesh” should not be understood as giving marital intimacy a poetic touch. It is far more literal than that.

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Genesis 2:21-24 speaks of the married couple as becoming “two-in-one-flesh.” This phrase specifies the uniqueness of the union between husband and wife. But its meaning goes far beyond that and has implications for a theology of the body in which science plays an important role in shedding light on its deeper meaning. The phrase should not be understood as giving marital intimacy a poetic touch. It is far more literal than that.

The Catechism of the Catholic Church (2357) teaches that “homosexual acts are intrinsically disordered” and makes it very clear that the Church can never approve homosexual activity. However, Cardinal Victor Manuel Fernández, prefect of the Dicastery for the Doctrine of the Faith, has issued a call for the Catholic description of homosexual acts as “intrinsically disordered” to be changed.

The science of immunology affirms the appropriateness of the expression “intrinsically disordered.” The immune system, containing approximately 100 billion immunological receptors, is designed to protect the body against invading substances that could be harmful. Therefore, it has the capacity to distinguish between the self and the nonself. Truly one of the wonders of the human organism, the immune system is able to keep a record of every germ (microbe) it has ever defeated so it can recognize and destroy the microbe quickly if it attempts to enter the body again.

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The science of immunology affirms the appropriateness of the expression “intrinsically disordered.”Tweet This

From the standpoint of the immune system, one would expect male sperm to be rejected as an alien substance. But this does not happen because of a rarely discussed factor that makes a critical exception: recognizing sperm as a friend, so to speak, and not as a potentially harmful substance. A mild immunosuppression contained in the seminal fluid sends a chemical signal to the woman’s body to accept the sperm that it carries. Because of this mild immunosuppressant, conception is possible and the new human being that is formed continues to be accepted. The single exception that the immune system makes allows life to continue.

The action of the immune system in making conception, gestation, and birth possible indicates that the two-in-one-flesh intimacy between husband and wife is more profound and more biological than it was earlier believed to be. In no other instance is this special intimacy possible than in the conjugal embrace. Here is a natural order and progression that is undeniable. It is natural and not man-made. It is intrinsic because it is rooted in the biology of husband and wife, and it is ordered inasmuch as one thing leads to another to make procreation a possibility.

The mild immunosuppressant changes the oncoming nonself into a self so that the intimacy between husband and wife becomes a relationship of self to self. Science, therefore, not only affirms Genesis but allows us to deepen our appreciation of its timeless message.

Now, if the semen is deposited in the “wrong place” (and we must be delicate here), the immunosuppressant still does its work, as nature intended. But this time, it suppresses what should not be suppressed. In other words, it creates an immunosuppressant environment which permits infections. Spermatozoa can penetrate somatic cells resulting in oncogenesis, the development of cancerous malignancies. In addition, the immunopermissive environment is favorable for the formation of tumors. All this, and much more, is well-documented in scientific journals.   

The science of immunology makes it clear that there is an intrinsic order of nature that leads from conjugal intimacy and the function of a mild immunosuppressant to new life. On the other hand, when this order is recklessly abandoned and a hostile environment is put in its place, serious pathologies can emerge. Disorder leads to havoc. There is a “wisdom” to God-created nature that is ignored at our peril.

Respecting the right order can produce new life. Choosing disorder can lead to death. The expression “intrinsically disordered” with reference to certain homosexual acts is highly appropriate and should not be changed. In fact, it is exactly as appropriate as pointing out that the expression “two-in-one-flesh is “intrinsically ordered.”

Disorder is a deviation from order. A particular disorder may not be recognized in itself if the order is unknown. Order is the standard while disorder is a departure from that standard. The purpose of the immune system is to protect the organism. When it fulfills this purpose, it is said to be working in good order. But when it breaks down and no longer protects the organism, it is clearly in a state of disorder. Blindness is not intelligible in itself. It is known as a disorder only when it is compared with sight. The best way to appreciate the fact that certain homosexual acts are disordered is to appreciate the order that is required to achieve procreation. 

Cardinal Fernández may have good intentions, but he is woefully ignorant of the science of immunology. Faith and science are compatible, as Pope John Paul II explains at length in his encyclical letter Fides et Ratio. “The Church remains profoundly convinced,” he writes, “that faith and reason ‘mutually support each other’; each influences the other, as they offer each other a purifying critique and a stimulus to pursue the search for deeper understanding.”

The function of the immune system, as explicated by science, both supports and deepens our understanding of the phrase “two-in-one-flesh.” We should welcome what science has to offer faith. To reject the words “intrinsically disordered,” which science has affirmed, is to weaken our faith.


  • Donald DeMarco

    Donald DeMarco is professor emeritus of Saint Jerome’s University and an adjunct professor at Holy Apostles College and Seminary. He is a regular columnist for the Saint Austin Review and the author, most recently, of Reflections on the Covid-19 Pandemic: A Search for Understanding.

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