Every Christmas, our attention turns to the manger scene and the profound mystery of the Incarnation: the eternal Son of God entering the world through the womb of the Virgin Mary. In meditating on this event, it is striking to note how Mary gave Jesus at least half of his human DNA—an undeniable biological reality that medieval thinkers, including Saint Thomas Aquinas, could not have imagined with their limited scientific knowledge. Modern genetics tells us that every mother contributes half the genetic material for her child, which means Mary’s own chromosomes formed part of Jesus’s humanity. This insight corrects a cornerstone of medieval biology, where woman was conceived as mere “fertile soil” receiving the fully formed “seed” from the man.
Aquinas, relying on Aristotle, expressed this view explicitly in the Summa Theologiae (I, q. 92, a. 1, Reply to Objection 1) where he refers to woman “as regards the individual nature” as “defective and misbegotten,” arguing that the male seed aims at producing a male child, while a female results from some defect in that process. Mary’s motherhood of the divine Person, however, radically challenges any notion that woman is a “defect.” In Mary, the world beholds a woman chosen before all ages to enflesh God’s Son—hardly the lot of a “misbegotten” being. Though Aquinas spoke with the assumptions of his age, Mary’s example shows that there can be nothing inferior or “defective” about the sex that enabled the Incarnation to take place.
Why would I be writing this article for Christmas this year? Well, did you know that Aquinas taught that women are defective humans by the very fact of being a woman? When I look around the world today and see how confused everyone is about sex and gender, I trace the confusion back to the failure of the Church to correct it’s own confusion. We are so quick to respond to the feminists hurt by “Patriarchy” that we elevate and hold up Mary! Don’t they know how important and special she is to us Catholics? And yet here we are either ignorant to what is so deeply embedded in our historical theology and anthropology that we don’t realize there is a contradiction between our Mariology and our Feminology, or if we do know, we sheepishly or conveniently ignore these misogynistic undertones.
In the same question, Aquinas also asserts (Reply to Objection 2) that woman is “naturally subject to man, because in man the discretion of reason predominates.” Even this claim withers under the light of Mary’s example at Christmas and throughout Scripture. In the Gospels, it is Mary who receives the angelic announcement, questions with reason—“How can this be, since I have no relations with a man?”—and gives her free and thoughtful yes. She is the one to provide Jesus a home in her womb, and she is the first to know intimately the extraordinary character of His birth. Joseph, for his part, remains the righteous guardian and head of the Holy Family, but it is Mary, Seat of Wisdom, who first understands what God is asking. The “discretion of reason” Aquinas felt belonged more fully to man appears in the Virgin’s discerning mind and heart, as she “kept all these things, pondering them in her heart” (Lk 2:19). In the Christmas drama, Mary’s dialogue with Heaven and her embrace of God’s plan show how erroneous it is to imagine women as merely second-tier in intellect or grace. Mary and Joseph clearly articulate how it is man and woman, the head and heart of the family, that albeit in different ways, lead, provide for, and protect the child.
Aquinas, of course, acknowledges Mary’s supreme possession of the highest order of grace amongst all humans ever created, but it’s important that we don’t disintegrate what is possible through grace from nature itself. Whatever grace Mary had was built on her nature as a woman. Was Mary special because God’s granting her a “fullness of grace” somehow superseded entirely what was in her by nature as a woman? Of course not. We are not piles of dung covered in snow. We believe in integration, in a core goodness being made in the image of God, and Aquinas’s assertion that “gratia non tollit naturam, sed perficit” (grace does not destroy nature, but perfects it.)
Whatever grace was able to do in Mary was a perfection of what was already in her by nature.
Aquinas adopts the Aristotelian notion of the male seed as the active principle conveying form and life, while the woman contributes merely the “material” on which this seed acts. To Aquinas’s medieval mindset, it was scientifically plausible to see the father as the principal source of a child’s being, with the mother’s body serving merely as a nurturing environment.
Yet Mary’s role at Christmas contradicts this entire premise. Far from being mere “soil,” Mary provided the flesh, the blood, and indeed the genetic structure of the incarnate Christ. The Holy Spirit overshadowed her, but her own body truly supplied half of Jesus’s chromosomes, making Him fully and truly human from her contribution as well as His divinity from the Father. (Where Jesus received the “y” chromosome to be a male is a matter of theological speculation). If Aquinas had access to the chromosomal science we now take for granted, he would have realized that the woman supplies as much of the “active principle” in forming a child as the man does. Mary demonstrates the extent to which each mother, far from being passive, participates actively in the mystery of new life.
These passages from Aquinas illustrate how even the greatest theologians can be constrained by the dominant biology of their era. In a world before microscopes or knowledge of chromosomes, it made sense to interpret procreation under the lens of Aristotle’s seed theory. But this Christmas, as we recall how the Son of God took flesh from a woman whose very body and DNA shaped His humanity, we see plainly how Mary stands in opposition to the idea that a mother is but a passive instrument. She is called “full of grace” (Lk 1:28), an active, free collaborator in the work of salvation, and the dignity she reveals shatters any diminished view of women.
While Aquinas’s errors may jar us, his broader legacy still greatly enriches the Church’s intellectual life. The Church recognizes that he could not have known what modern genetics teaches, nor could he have anticipated the dogmatic definition of Mary’s Immaculate Conception centuries later. Yet Mary’s singular privilege does more than show us her personal greatness; it also underscores how God sees woman in general: not as lacking or inferior, but as fully capable of embodying and cooperating with the divine plan. Where medieval science cast her as mere “fertile soil,” God cast her as the living Ark of the New Covenant, overshadowed by the Holy Spirit, bearing in her womb the very Son of God.
Many faithful Catholics (always men) react quite strongly when I write or speak about this issue. Yet the Christ Child came to cause discomfort where necessary and disrupt cultural indignities towards humans wherever they were found. We can let Him disrupt our own cultural indignities today so that we might all be reformed and renewed in the full light of God’s truth. If you, the reader, think this is a non-issue, and our Church has no mark of misogyny to correct, then be well my friend, Merry Christmas and move on.
If you are tracking what I’m saying here, though, let’s be grateful for St. Thomas Aquinas giving us a clear understanding of the role of grace and the powerful reality of God’s collaboration through, with, and in our natural humanity, as well as for Mary, blessed among all women, who teaches us even more about who we are – men and women as equally endowed children of God – in His divine plan. This is the light of Christ, and the truth and Good News about all of us, that needs to be shared with “all nations.”
At Christmas, the manger scene and the entire story of the Incarnation testify to Mary’s active and irreplaceable role. That role corrects the notion of woman as a flawed image of humanity and replaces it with a vision of radiant dignity. In Mary, we see how the Creator from all eternity intended woman to stand—free, holy, intellectually engaged, and crucial to the unfolding of salvation history. By pondering Mary’s yes, we more fully grasp the depths of human cooperation with God’s work, and we are gently reminded that the errors of past ages do not negate the fullness of truth that Christ reveals. This season, gazing upon the Christ Child held in His mother’s arms, we recognize that the miracle of Christmas came through a woman who was neither particularly defective nor subordinate by her feminine nature, but exalted beyond measure—precisely because she was chosen to share, in her female body, the work of our redemption.