Meanings of Christmas: Literal truth or a symbol of faith?: Our series for Christmas week opens with a consideration of belief in the miracle of the Virgin Birth by Professor R. J. Berry, Professor of Genetics at London University.

ABOUT one in every seven of the British population will go to church or a carol service over Christmas. Virtually all of them will sing 'O come all ye faithful . . . God from God, he who abhors not the virgin womb' and only a slightly smaller number 'Hark, the herald angels sing . . . Christ . . . offspring of a virgin's womb'. Presumably the truly faithful will believe these words. What about the rest - including those who will not go to a formal service, but will sing along with the carol service from King's College, Cambridge, or even unsolicited musak?

Will they put the Virgin Birth in the same bracket as Father Christmas? Will there be many who follow (or even understand) the Bishop of Durham's claim that the Virgin Birth is not literally true, but 'an inspired symbol of a living faith about the real activity of God'? Bluntly: is it important or necessary to believe that Jesus was born of a virgin, and what are the consequences of disbelieving it? Put the other way round, why should we believe in the Virgin Birth of Jesus?

The Virgin Birth is part of orthodox Christian belief. Matthew's Gospel tells us,

Mary was betrothed to Joseph; before their marriage she found she was going to have a child through the Holy Spirit . . . this happened in order to fulfil what the Lord declared through the prophet: 'A virgin shall conceive and bear a son, and he shall be called Emmanuel', a name which means 'God is with us'.

In Luke's gospel we read that an angel appeared to Mary with the news that she will conceive and give birth to a son, 'and you are to give him the name Jesus'. Mary's reaction was 'How can this be? I am still a virgin'; the angel's reply was 'The Holy Spirit will come upon you, and the power of the Most High will overshadow you; for that reason the holy child to be born will be called the Son of God'. The Apostle's Creed requires us to affirm 'Jesus Christ conceived by the power of the Holy Spirit and born of the Virgin Mary'.

This is too much for many people to swallow. Virgins simply do not have babies, much less male babies. Even if parthenogenesis ever occurs in humans in the way it does, for example, in bees and green-fly, a human male needs a Y-chromosome, and this can only be contributed by a Y-bearing sperm from a man.

So goes the objection to the virgin birth of Jesus. But if it did not happen, we have to use special pleading to dispose of the Bible teaching that describes it. For example, the word translated 'virgin' in Isaiah's prophecy literally means a 'young woman'. More difficult are the Matthew and Luke passages; they have been rejected by some as mere folklore accounts, based on pagan stories of divinely begotten heroes. Such selective demythologising is intellectually dubious and theologically dangerous.

Is a virgin birth possible? In 1955, the Sunday Pictorial advertised for mothers who genuinely believed that they had given birth to a parthenogenetic child, ie one born without fertilisation. Nineteen women replied. Eleven were eliminated quickly, because they believed that a virginal conception was one in which the hymen remained intact. The other mother-daughter pairs were typed for as many blood groups and similarly inherited traits as were available at the time. Seven of the remaining eight were found to have genes in the child that could not have come from the mother. The final pair was skin-grafted, mother to child, and child to mother. The grafts were rejected but not as quickly as expected. It remained possible but not proven that this last child was a virgin birth. Such an event is not completely beyond rational bounds: unfertilised rabbit and mouse eggs can be stimulated by chemical or physical shocks to develop into apparently normal embryos. Although most of these die as early embryos, at least one parthenogenetic rabbit is said to have been born alive. Human eggs will also respond to shocks in a similar way.

Nowadays a much more critical test of mother-daughter matching could be carried out using DNA fingerprinting. However it can be objected that such evidence is irrelevant, because no woman could give birth to a male child by parthenogenesis, since she has no Y-chromosome to contribute to her child. In fact this is not a complete barrier. We now know that there are women who are chromosomally XY (the male constitution), but who have a mutation so that their cells do not 'recognise' testosterone, and hence they mature as females. There are also men who are XX, and are still male despite having no Y chromosome. In their case the male determining gene has been broken off from a normal Y chromosome and incorporated into one of the Xs. It does not require much imagination to envisage a situation where a normal female has a mutation to a male determining variant on one of her X chromosomes, so that she produces ova which will give rise to males (since the Y chromosome almost certainly arose from an X chromosome in the evolutionary past, this is not too far-fetched). If an ovum in a woman with one of these mutations develops without fertilisation, the result could be a boy born to a virgin. The biological mechanisms exist.

But speculating about the possible causes of extremely rare events (miracles, if you like) does not prove or disprove them. Nor does it help us to make a definitive judgement on the more general question as to whether or not miracles ever occur. It is an act of faith to believe that a particular miracle has happened; it is no less a statement of faith to assert that miracles never happen. The oft-repeated argument by the 18th-century philosopher David Hume that there are no grounds for a rational belief in the miraculous, since the probability of a miracle is less than the probability of a false report about it, is a tautology.

As far as virgin births are concerned, everyday experience is that they must be very rare, if they occur at all. But it would be improper in the light of our knowledge of genetics and embryology to claim that they can never happen. However, even this statistical argument does not help when we come to the particular Virgin Birth which traditionally took place on the first Christmas Day, because it was an explicitly supernatural event; Mary conceived 'through the Holy Spirit', the son born to her 'came down from heaven', 'was sent by (God) the father', and 'came into the world'. The real issue is not whether a virgin birth is outside credibility, but whether there is a God who creates and upholds the world and all that is in it. If there is, there need be no limit about the way he chooses to act, beyond being consistent with his own character. Indeed if the Christ-child was to be truly man and truly God, it would be surprising if he did not mark his continuity with humankind by normal birth after normal gestation, while at the same time emphasising his discontinuity by some event like a virgin birth.

The real Christmas miracle is the Incarnation, not the Virgin Birth. God took human form, that He might redeem us and make it possible for us to come to Him. The Virgin Birth of Jesus Christ was a secondary miracle. The most important fact of Christmas is God's humbling Himself to come among us, Emmanuel.

It is right to examine faith and dogma with all our faculties; baseless credulity is a sin - a disservice to the God of truth. But in such examination, we have to take into account the possibility of a God who acts. Let us not be led astray by cunningly devised fables of clever men and women; let us stand fast in the faith of the one who became flesh and made His dwelling among us, full of grace and truth.