Is Jesus Christ the "Genetic Twin" of the Blessed Virgin Mary? Let’s ask St Thomas Aquinas…

A reader recently wrote in with a comment relating to the physical likeness of Mary and Jesus.
Dear Dr. Marshall, 
I just bought your book on St. Paul at Amazon because I wanted to read about Paul’s Mariology. I was NOT disappointed. Your many brilliant insights brought tears to my eyes. 
Have you ever considered the fact that Mary and Jesus were IDENTICAL TWINS??? Jesus was made from the DNA of Mary just as Eve was made from the DNA of Adam. 


Joseph Allen Kozuh, Ph.D. Austin, Texas

Dr. Kozuh, thank you for the kind words about the The Catholic Perspective on Paul. Soon I’ll be explaining how I’m going to personally guarantee all my books. That is, if you buy one of my books and don’t like it, just write me and I’ll send you a personal check to refund your money.

Now on to your comment about Jesus and Mary as twins. I’m not a geneticist. I’m a philosopher. That being said, it seems that Our Lord Jesus Christ would not necessarily be a male clone or “genetic twin” of Mary. We can only go on what Doctors of the Church have written on the matter while recognizing that the Catholic Church has not ruled dogmatically on this question. 

Now then, the Catholic Church has condemned the heresy of Valentinus who wrongly taught that Our Lord Jesus Christ did not take genetic material from Mary, but rather passed through her “like water through a straw.” The heresy of Valentinus wrongly taught that Mary was merely an incubator of Christ, but not His true mother. This heresy is clearly incorrect and does not account for many teachings in the Gospels of St Matthew and St Luke.
So we know from Catholic magisterial teaching that Christ acquired his genetic material from Mary. He was derived from her human substance and was truly His mother and thus the Mother of God – Christ Himself being divine.
With the advent of modern genetics, the question arises: Did Christ derive all of his genetic material from Mary? Well, women have XX chromosomes and men have XY. It seem then that the Holy Spirit provided extra genetic material which would be combined with the genetic code of Mary. To speak clearly, Christ could not have been male if the Holy Spirit did not add something. Since this is the case, Christ would not be the genetic twin of Mary. Their genetic code was similar but not identical.
It’s true that the Church Fathers did not know what we know about DNA and chromosomes. Saint Augustine referred the active principle of human conception as the “seminal virtue.” Saint Thomas Aquinas explains how this applies to Christ, Mary but also to the supernatural operation of the Holy Spirit at the Incarnation:

Since, therefore, the Blessed Virgin was not Christ’s Father, but His Mother, it follows that it was not given to her to exercise an active power in His conception: whether to cooperate actively so as to be His Father, or not to cooperate at all, as some say. whence it would follow that this active power was bestowed on her to no purpose. We must therefore say that in Christ’s conception itself she did not cooperate actively, but merely supplied the matter thereof. Nevertheless, before the conception she cooperated actively in the preparation of the matter so that it should be apt for the conception. (Summa theologiae III, q. 32, a. 4)

In modern terminology, the Holy Spirit added something to the genetic material of Mary at the conception of Christ. As St Thomas says, Mary cannot be both the Mother and Father of Christ. The biological code that would have come from a biological father was somehow supernaturally supplied by the Holy Spirit, for example, the Y chromosome. By the way, this doesn’t mean that the Holy Spirit is the Father of Christ, as St Thomas Aquinas explains at Summa theologiae III, q. 32, a. 3.
Still, I really do think that Our Lord and Our Lady looked very much alike even though they were not genetic twins. It seems fitting that as New Adam and New Eve they would have a certain biological resemblance even though they were not genetic twins. There is also an old tradition that St Jude (a cousin on Mary’s side) looked very much like Jesus Christ our Lord. If Jude looked like Christ, then Christ certainly resembles Mary.
Perhaps some of our readers would like to weigh in. Do you think that Mary and Christ looked alike? Also, aren’t you glad that we Catholics have great saints like Saint Augustine and Saint Thomas Aquinas to steer us in the right direction?! Sola scriptura just doesn’t answer these kinds of questions. Please leave a comment.
For those interested in my book The Catholic Perspective on Paul (which has a section on Paul’s often ignored Mariology), here’s the link. I’m so confident that you’ll find this book helpful, I’ll personally guarantee it. If you don’t find the book helpful or informative, just let me know and I’ll send you a personal check for the refund. The book is currently on sale, down from $16.95 to 14.95 on

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HT: Ben Olsson, MD

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