In an echo of the great 19th- century clashes between Science and Religion, the scientific journal Nature today publishes a stinging catalogue of errors in the church's understanding of basic biology. But its author, Dr John Godfrey, a geneticist from the University of Edinburgh, denied that it was an attack on the church.
Although he is not himself a Catholic, Dr Godfrey suggests that the church has even got its theology wrong, by abandoning the views of St Thomas Aquinas, whose theological writing earned him the epithet of the "Angelic Doctor".
Dr Godfrey believes that the church's opposition to birth control "have implications for everyone, because the world is a finite place"; he is concerned about the growth in population and the depletion of natural resources.
The Pope commits many errors in his book, Crossing the Threshold of Hope, according to Dr Godfrey. He "accepts the misconception that there is an instant when fertilisation happens". In fact, the process of fertilisation is complex and takes about two days. It can involve more than one sperm, at least for a while, thus making it impossible to establish any "instant" when the fertilised egg acquires a unique genetic identity.
Even "activation" - the process which finally inhibits fertilisation of the egg by many sperms - occurs rapidly but not instantaneously. Activation is not the "moment" of conception either, since it precedes the mingling of the sperm's DNA with that of the egg, and so happens before the genetic identity of the embryo has been established.
For about the first four days, according to Dr Godfrey, all the genetically determined properties of the fertilised egg are maternal; only after this do the paternal genes begin to act, with gene expression characterising the new individual.
Dr Godfrey writes: "The picture of the nascent human that emerges from modern embryology is one of seamless change.''If this picture is accepted, then it means that the moral and religious status of the embryo would change and develop in parallel.
Dr Godfrey concludes that the Pope should "consider afresh" the teachings of Aquinas and the lessons of modern biology.