The Bible tells us that Jesus Christ was the product of a virgin birth to his mother Mary 2,000 years ago. Is there a natural mechanism that could explain this event? The answer would seem to be no.
This leaves two options. Either the impregnation of Mary and the subsequent birth was a miraculous event, or else it occurred in the conventional natural manner and the account of the virgin birth is a myth.
A virgin birth means a birth to a mother who was not impregnated through the sexual process, i.e. by the union of a sperm from the father with an egg from the mother. They are not uncommon in the general biological world.
Bacterial cells, for example, reproduce by binary fission, whereby the cell grows, duplicates its genetic material and then divides into two identical daughter cells, each containing copies of the mother's genetic material.
Several varieties of insects can reproduce without the aid of sperm and we know that this is also possible with plants. The virgin births that occur in certain animals are fundamentally different in mechanism from the propagation of plant cuttings.
In the former case, we are dealing with a process called parthenogenesis, in which a female egg cell divides and develops into an embryo, and subsequently into a complete new-born offspring, without any help from a sperm.
With plant cuttings, a small piece cut from a whole plant is itself planted and grows into a new plant, which is a clone of the plant of which it once was just a twig.
Our bodies are made of two types of cells: somatic cells and sex cells. Somatic cells make up the various tissues and organs, i.e., muscle, liver, etc. The sex cells - sperm in male, egg in female - are involved in procreation. The hereditary material (genes) in all cells is contained in bodies called chromosomes.
Somatic cells (in the human) contain 23 pairs of chromosomes, i.e., two sets of 23 chromosomes per set. One set comes from the father, the other from the mother. Sex cells contain 23 single chromosomes, some of which came from the father and some from the mother. When a sperm cell unites with an egg cell, 23 pairs of chromosomes are again restored.
Sex is determined by one of the 23 chromosomes, which comes in two varieties: X for female and Y for male. Female somatic cells contain two X chromosomes (XX). Male somatic cells contain one X and one Y chromosome (XY). Sex cells contain only one sex chromosome.
The egg cell always contains an X chromosome; half the sperm cells contain an X chromosome, the other half have a Y chromosome. If an X sperm fertilises an egg, the offspring will be female (XX). If a Y sperm fertilises an egg, the offspring will be male (XY).
In parthenogenesis, an unfertilised egg cell containing 23 single chromosomes duplicates its genetic material to produce 23 pairs of chromosomes (the somatic number), and the cell then divides by binary fission to produce two daughter cells.
The two daughter cells divide again, and cell division continues, to produce an embryo which develops eventually into a complete new offspring. No sperm cell is involved. Obviously if parthenogenesis occurred in a woman, all the offspring would be female since all the sex chromosomes would be of the X variety.
In the late 1950s scientists discovered populations of all-female lizards that reproduced exclusively by parthenogenesis. Also in the 1950s, parthenogenesis was noted in some breeds of turkeys.
Recently parthenogenesis has been reported to occur in some rattlesnakes. It is postulated that parthenogenesis arose in certain species as a fall-back device that allows the female to reproduce under conditions where males are not available, e.g. when females become isolated geographically from the males.
So far, no case of parthenogenesis has ever been seen in a mammal and, despite intensive efforts, parthenogenesis leading to a viable embryo has never been experimentally induced in a mammal. In fact, research on mice has shown that in order for an egg to develop into a viable embryo, it must contain a set of chromosomes from both the father and the mother.
When mammalian eggs are experimentally manipulated so that they contain two sets of egg chromosomes, or two sets of sperm chromosomes, they fail to develop into viable embryos.
The reason for this is that, in the mammal, chromosomes from the male and chromosomes from the female are marked or imprinted differently. This means that they contain internal instructions that may cause the expression and functioning of a gene inherited from the father to differ from that of the same gene inherited from the mother.
Neither chromosomes from the male, nor chromosomes from the female, even when doubled up, are complete, i.e., sufficient to develop into a viable embryo. Among vertebrates, imprinting seems to be exclusive to mammals, which explains why parthenogenesis is occasionally noted only in other species.
So Christ was not the product of parthenogenesis in Mary. In any event, if parthenogenesis could have occurred in Mary, the offspring would have been female, not male, because the process would have produced two X chromosomes.
If we rule out parthenogenesis, but accept the virgin birth, then half of Christ's chromosomes came from Mary and the other half came from the Holy Ghost (or perhaps, more appropriately, from God the Father).
William Reville is a senior lecturer in biochemistry and director of microscopy at UCC.