Do we need to postulate a physiological mechanism for the Virgin Birth?  Is it not best to regard it as a miracle, pure and simple?  Possibly.  But the question then arises as to how this safeguards the doctrine of our Lord’s humanity.  Moreover, if it is the case that God loves natural processes (he created them!) and uses ‘pure’ miracles sparingly (often preferring ‘miracles of timing’) then we have further reasons to enquire if any account can be given of the genetics of the virgin birth.

Lincoln (Born of a Virgin?) states the problem like this:

‘According to our present knowledge, to be a fully human male Jesus would have needed an X chromosome from Mary and a Y chromosome from a human father. If we still wished to hold to a literal virginal conception, God would have had to supply de novo either the genes that had come from a male or both sets of genes. In the latter case Mary would have been simply the surrogate mother of this embryo, which would have no real continuity with the human race to this point, although it could have been a copy of a human being with its genetic endowments. In the former case, if God provided the Y chromosome, what does this say about the normal encoded genetic information a male as part of the evolving human species would have received from a father? Does one then have to say that God copied the sort of genetic information that Joseph or some other first-century Jewish male might have supplied? It appears to be extremely difficult to hold that a divinely supplied copy of this genetic endowment still allows for Jesus to share fully our evolved human embodiment.’

So, what genetic mechanisms might be considered?

1. Miraculous provision of a Y chromosome

It was noted above that some who hold to a birth without the biological participation of a father believe that the genetic material he would normally contribute (or, at least, the Y chromosome) was supplied miraculously

This supposition goes back at least as far as Thomas Aquinas (cited by Lincoln), who maintained that

‘the divine power, which is boundless, completed what was necessary for the foetus’

As Lincoln states, this places a serious question mark over the full humanity of Jesus (see Heb 2:17).  In the ancient world, the woman was thought to be the provider of the entire substance of the child, with the male contributing only the ‘life force’.  Thus the theologians of the early church were able to use the doctrine of the virgin birth as a defence against the charge of docetism.  But now that we understand that the mother and father contribute roughly equally to the baby’s biological substance, it appears that the doctrine of the virginal conception, actually invites that very charge of docetism:

‘Without complete human DNA Jesus would be a semi-divine or wholly divine special creation that appeared to be human.’

Lincoln also acknowledges the argument which maintains that belief in a literal virginal conception tends to demean sexual bonding and the family life to which it contributes.  But, as Lincoln responds, the scriptural birth narratives are primarily about the uniqueness of Jesus and not about ‘the family’.

2. XX Male

In a recent book (Science and the Bible: Modern Insights for an Ancient Text) David Instone-Brewer offers a fascinating, if tentative, possible explanation from a genetic point of view.

Instone-Brewer begins by noting the parthenogenesis has been observed naturally among some animals, but not mammals.  However, it has been induced in rabbits, mice and monkeys, although rarely producing live births.  So, from a scientific perspective a virgin birth is not impossible, but not something that we would expect without divine intervention.  We would expect such a birth to be female, because the absence of a father means the absence of a Y chromosome.

The theological problems, however, with a virgin birth seem formidable.  If Jesus lacked a human father, does this not call into question his full humanity?  This raises the wider question of how Jesus could represent women, for example, or disabled people.

Enter ‘XX men’.  A person with two X chromosomes is normally female.  But there is a condition in which someone with two X chromosomes is actually a male.  There would be about 8,000 such men in the US today.  Some would have been born with sexual ambiguity, or would have developmental problems diagnosed later on.  But others have normal levels of testosterone, and therefore be indistinguishable from XY males.  The XX-male syndrome usually results fropm genetic crossover, whereby the testosterone gene SRY, which is on the Y chromosome, is swapped with a similar gene on the X chromosome.  (It is of interest that the International Olympics Committee is aware of this issue, and now defines males by amount of testosterone rather than by sex chromosomes).

On the principle that God loves his creation, and he loves to use natural processes, the simplest and most natural way in which he could produce a male by parthenogenesis would be by creating an XX-male.  The miracle would be by doing so in a particular way and at a particular time, when the chances of it happening naturally were extremely improbable (though not impossible).

It should be noted that one factor leading to the extreme improbability of the birth of an XX-male by parthenogenesis is that the genetic translocation required normally (always?) comes from the process of sperm production in the father.  But in parthenogenesis there is, by definition, no father.

R.J. Berry (formerly Professor of Genetics at University College London) writes:

‘Some men are apparently XX (the female complement). Examination shows that in them the male determining factor of the Y (a single gene, Sry) has been translocated onto another chromosome. If the translocation was to an X chromosome and if that chromosome was inactivated in early development (one X chromosome is always inactivated or Lyonised; this inactivation is random, so normally half of the cells will express one X and half the other one), the carrier will have a female appearance, but have the capacity of transmitting the male determining gene. Men with XX chromosomes are sterile, but Jesus never married and we do not know if he was fertile (although he was, of course, ‘perfect man’ in the theological sense).’

The mechanism has some positive theological implications:

• As noted, God works more closely with natural processes, and does not have to produce a Y chromosome from a one-off miracle.
• A person with two X chromosomes arguably represents females as well as males.
• An XX-male has a link with others who are ‘different’ from the general population in some way, including who are marginalised because of other kinds of genetic syndrome.
• A person with ambiguous sexual characteristics would have been excluded from the Temple.  Once again, Jesus would be identified with other despised minority groups.

Instone-Brewer recognises that this explanation is merely ‘possible’.  Moreover, he agrees that it may feel ‘wrong’.  But, if it feels ‘wrong’ then that may be because we are expecting Jesus to be perfect and utterly ‘normal’ in his physical makeup.  But this would be to deny his true humanness and to undermine the truth and significance of his incarnation.

An objection to the idea that Jesus carried any form of congentical abnormality might be raised on the basis of 1 Pet 1:19, and its assertion that Jesus was the perfect ‘lamb without blemish and without spot’ (see also Heb 10:5).  But this doesn’t seem to me to be a decisive objection.

See also this, from Science Direct

3. Parthenogenic Chimera

The above is interesting, but, of course, speculative.  The most obvious question to be answered is: if Y-chromosome material was translocated to an X chromosome, where did it come from?

R.J. Berry writes:

‘Parthenogenesis by itself cannot account for the birth of Jesus: human males carry a Y chromosome, and it is natural to assume that Mary did not carry a Y chromosome since this would have led to her possessing male characteristics as well as being sterile. This is a reasonable assumption, but it is not necessarily correct: there is a mutation which has the effect of preventing target cells ‘recognising’ the male hormone testosterone; such people are chromosomally XY (the male complement) but appear as completely normal females, albeit sterile and lacking a uterus.  However the differentiation of the sex organs in such people is very variable, and it is possible to envisage a situation where a person of this constitution developed an ovum and a uterus. If this happened, and if the ovum developed parthenogenetically, and if a back-mutation to testosterone sensitivity took place, we would have the situation of an apparently normal woman giving birth without intercourse to a son. I am not proposing that this was the mechanism behind Christ’s conception, but merely suggesting a method by which it could have occurred  recognising that the possibility would be extremely unlikely and arcane—but that is what the Virgin Birth was).’

Further comment

(a) It seems to me that an alternative mechanism might be considered, in which Mary had 46,XX/46,/XY chimeric condition.  In this rare condition, some of the cells of the body contain XX sex chromosomes, while others contain XY chromosomes.  This condition is consistent with a normal female (or male) phenotype and fertility (see this article, from the journal Human Reproduction).  It could conceivably account for the contribution of a Y chromosome to our Lord’s genome.

(b) Alternatively, it seems possible that Jesus himself was a parthenogenic chimera.  This article, published in the journal Medical Hypotheses, recalls a report in 1995 of a ‘parthenogenetic event resulting in a viable (male) baby’. It was concluded that this baby was a parthenogenetic chimera.  These authors hypothesise that an unknown number of such events may have occurred, that may have hitherto been undetected precisely because the child had no abnormalities of concern.

(c) But there is a further possibility: that the Jesus’ entire genome was created de novo.  The theological objection to this, oft-stated, is that it would be entirely inconsistent with our Lord’s complete humanity.  How could he be truly human, if in his body he lacked continuity with the human race?  How, indeed, could he be descended from David? Answers to such objections would begin with the assertion that both the first Adam and the last Adam were special creations of God, and yet fully human.  But it is uncertain where the rationale would go after that.  The comment of Donald MacLeod needs to be weighed:

‘Christ’s humanness was created not ex nihilo but ex Maria: of her substance. She contributed to him exactly what any human mother contributes to her child: ovum, genes, ordinary foetal development and ordinary parturition. He was, in an entirely proper sense, ‘the fruit of her womb’ (Lk. 1:42, RSV).’ (The Person of Christ, p42)