In Search of Christ's Chromosomes

One of the great controversies of medieval art was whether to depict Adam with a navel. Shorn of its scholastic complexities, the question boiled down to this: since God had created Adam directly, as the the first man, any remnant of a normal birth process was at best useless decoration and at worst a lie. God could not possibly stoop to either. On the other hand, to depict him without a navel would indicate that he was different from all other human beings, a distinction enjoyed only by Christ and the Virgin Mary, both of whom, as it happened, had navels.

That controversy has long since died down. Most Christians, with the exception of an irreconcilable horde of creationists, now accept some form of evolutionary origin for humanity. God,in the modern view, would not leave irrefutable evidence of His (or Her, or Its) existence for us to stumble upon. That, after all, would be an infringement of free will; it would remove the need for faith. Instead, at some point in the evolutionary transition from hominid to human, the Deity acknowledged Adam's fully human status by giving him a soul. Adam's navel was simply an inheritance from his (non-human) mother.

Far from science being antithetical to religion, modern theology takes a much more subtle approach. Science is seen as complementary, as revealing God's universe in all its beauty. A Catholic priest, Georges Le Maitre, for example, was one of the originators of the Big Bang theory. God, in this view, is not some celestial wizard, arbitrarily demonstrating his omnipotence. Rather, he created the laws of the Universe and allowed them to take their course. It would be simply inconsistent of him to break His own laws.

But, while theologians may accept the new ideas of cosmology and evolution, there is another question, central to Christian belief, that seems much more difficult - if not actually impossible - to reconcile with modern science. If Jesus, as well as being God, was truly a man and was born of a virgin, then how exactly did his conception come about and what was his genetic constitution? What, in short, was in the chromosomes of Christ?

The literal virginity of Mary has been a source of some theological dispute through the centuries, but majority opinion (ie, the Roman Catholic Church) holds that she was indeed a virgin at the time of Christ's birth and remained so for the rest of her life. Assuming that was so, then there remain two possible routes for conception - artificial insemination and parthenogenesis.

Historically, both have had their supporters. Prime suspect for the first is the Holy Ghost, the member of the Trinity that reaches the parts others cannot. The idea of some sort of divine insemination - the ear was a favourite orifice of entry for the holy seed - is common in early commentaries. in her pellucid study of the cult of the Virgin, Alone of all Her Sex, Marina Warner traces the development of the idea - "conceived by the Holy Ghost, born of the Virgin Mary", in the words of the Apostle's Creed - back to Greek myth. The "Paraclete" is often depicted as a dove in paintings, and Zeus, for example, took the form of various birds - a swan with Leda, an eagle with Aegina, a cuckoo with Hera - in many of his seductions.

Gradually, the feminine nature of the dove gave way to more virile notions, to the point where, in the 17th century, one of the first systematic theologians of the Virgin, Francisco Suarez, was moved to deny any sexual aspects of the encounter. "The Blessed Virgin in conceiving a son neither lost her virginity nor experienced any venereal pleasure."

No sybarite, our Francisco. Leaving aside ideas of divine hanky-panky, it would, of course, have been open to the Deity to have used some form of artificial insemination, making Christ the world's first test-tube baby. However, modern theology tends to look rather sniffily on such crass intervention in human affairs.

One way out of this dilemma would be to consider a materialist variation on the theme - self-fertilisation. Could the Blessed Virgin have been a hermaphrodite? A little theological ingenuity could surely brush aside objections over loss of virginity and "venereal pleasure", in asserting that God somehow bought both organs of reproduction into play in the conception of his son.

God, of course, is capable of anything, but biologically it must be considered the most outside of bets. True hermaphrodism, where both male and female organs are fully functional, is common in plants and in creatures like worms and barnacles, but even so there are strong mechanisms preventing self-fertilisation. Among mammals it is virtually unknown, although there has been at least one case reported, in the Netherlands in 1990, entitled "Combined Hermaphroditism and Auto-fertilisation in a Domestic Rabbit".

In this study, an apparently true hermaphrodite rabbit served several females and sired more than 250 young. of both sexes. In the next breeding season, the rabbit, which was housed in isolation, became pregnant and delivered seven healthy young of both sexes. It was kept in isolation and when autopsied was again pregnant and demonstrated two functional ovaries and two infertile testes.

There appear to be no similar reported human cases, although there are people who exhibit characteristics of both sexes, such as having breasts and a penis. This may be due to hormonal imbalances or, more rarely, to chromosomal mosaicism, in which the cells in the body, instead of all having an identical set of chromosomes, have differing sets, some male and some female. The probability of self-fertilisation in such cases must be vanishingly small. In any event, invoking the idea that the Blessed Virgin was not a true woman, rather a freak of nature, is unlikely to be appealing to true believers in the virgin birth.

So parthenogenesis seems the better bet. The idea that life can somehow generate itself goes back at least as far as Aristotle and was taken up by a number of Christian theologians, including Aquinas. The notion of spontaneous generation remained current until the late 19th century, when Pasteur finally disproved it. Scientifically, parthenogenesis, the ability to reproduce asexually, is an established fact in creatures ranging from bacteria to birds. What could be more natural than extending the idea to humanity? Religion and science in perfect harmony.

Up to a point. It is true that a number of animals and plants are either partly or exclusively parthenogenetic and, indeed, it is not really clear why sex exists at all. After all, if the name of the game is to get as many of your genes into the next generation as possible, what is the point of sharing them with a partner and so halving your genetic contribution to your offspring? In plants and insects, parthenogenesis is common. Blackberries and dandelions have several species, that reproduce asexually, as do many aphids and fleas. Examine a common greenfly and you will often see its body contains young waiting to be born, which in turn, when looked at under a microscope, can be seen to have their young already developing inside them. That way, when conditions are right, their numbers can increase prodigiously, as any gardener knows.

However, as you move up the scale of bodily complexity, asexual reproduction becomes much rarer. It is found in some fishes, frogs and salamanders and, among reptiles, in at least two species of lizards. In one of these, the genus Lacerta, found in Russia, all individuals (they are all female) are members of a single clone. Grafts from one will be accepted by another. This indicates that the species originated from a single individual very recently, no more than a few thousand years ago.

The general conclusion is that among the more primitive classes of vertebrates, parthenogenesis has probably arisen many times, but died out almost as quickly as it arose. While there is no general agreement on the exact function of sex - whole libraries have been written on the subject and many distinguished biologists have pondered its mysteries - it does seem to be necessary for the longterm survival of species.

There are no known examples among birds and mammals in the wild, and certainly no unequivocally accepted cases among humans, although there remains the interesting case of domestic turkeys. It has been found that the infection of unfertilised eggs with certain viruses can cause embryos to develop in some strains of turkey. This raises the intriguing possibility that just as God may be a computer virus (as Richard Dawkins has pointed out, famously, in these pages), so his Son and Incarnation on Earth might have been the result of a real virus.

Alas, it can be raised, only to be dismissed. in mammals, unlike in birds, the birth of any parthenogenetic offspring, especially a fully functioning male, as Christ was claimed to be, seems to be impossible. To see why, we need to look a little closer at the make-up of human chromosomes.

Every cell in the human body except the gametes (ova and sperm) has 46 chromosomes, arranged in 23 pairs, one of each pair coming from each parent. In 22 of these pairs, both chromosomes are, to all intents and purposes, identical. The remaining pair is the one that determines sex. If they are identical (known as XX because of their appearance under the microscope), then the cell (and hence the person) is female; if they are non-identical XY), then it is male. Gamete cells, however, only have 23 chromosomes. On fertilisation, sperm and ovum fuse to produce the full complement. Ova contain only X chromosomes, while sperm may have X or Y. Consequently it is the sperm, exclusively, that determines the sex of the offspring.

Now, in parthenogenesis, the 23 chromosomes in the ovum have somehow to double themselves and then cell division must proceed normally until birth. The first step undoubtedly occurs quite frequently in nature. But the single X in the ovum can only double to XX in the full set - the sex of any parthenogenetic offspring must inevitably be female.

The second, and seemingly insuperable problem, is that every chromosome in mammals seems to be imprinted with the information that it came either from the mother or father. Cells that do not have chromosomes from both do not develop normally.

One of the commonest benign tumours of the ovary, called teratomas, are actually caused by ova with a doubled set Of 46 chromosomes starting to develop. In a bizarre approximation to normal development, they grow many sorts of tissue - connective, nervous, bone - but no placenta. implantation is impossible. Curiously, when a cell with the converse error, 46 chromosomes exclusively from the father, starts to develop, then only placental tissue is produced, no embryo, let alone Infant Jesus meek and mild.

Recently, there has been a very interesting twist to this tale, described in New Scientist as "the closest thing to a virgin birth that modern science has ever recorded". A young boy, examined in Edinburgh, turned out to have blood cells with XX chromosomes that came exclusively from his mother, while the rest of the cells in his body were the normal, masculine XY. The scientists examining him speculate that it was a case of partial parthenogenesis. The original, unfertilised ovum divided once and then one of the cells was fertilised by a sperm, which allowed the part-fertilised embryo to develop normally. This must be an exceedingly rare event - the Edinburgh team do not expect to see another - and in any case it would hardly be what the Pope has in mind when he contemplates the finer points of Mariology. Whichever way you look at it, and however hard you try, it seems impossible to escape the conclusion that the virgin birth and modern science are simply incompatible.