Javier is only a week old, but already he is at the centre of a growing political storm.

In the first case of its kind in Spain, he was born through stem-cell selection because his parents hope that he will provide a cure for his chronically ill brother, Andrés.

The six-year-old suffers from a congenital form of anaemia, but material from Javier's umbilical cord may help to cure him because screening has ensured that his new brother is free of the condition.

However, the method of Javier's birth has brought criticism from the Roman Catholic Church and “pro-life” groups, who condemn stem-cell screening. They say that many other potential human beings are “killed” in the process because they may have future medical problems.

Spain legalised stem-cell research only in 2006 and Andalusia, in the south, where Javier was born, became the first region to allow embryo screening as a public health right.

Dubbed the “miracle baby” by Spanish media because of the pioneering techniques used for his birth, Javier will be the donor of stem cells from his umbilical cord for a bone marrow transplant on his brother.

Andrés suffers from beta-thalassaemia, a severe form of anaemia that requires constant blood transfusions and which means that he could die from heart problems before reaching 35.

His parents, Soledad Puertas and Andrés Mariscal, from Seville, are now pinning their hopes on their newborn son. Ms Puertas, 35, said: “We knew about a few investigations to do with stem cells but little more. We started to ask some doctors and once we had all the permissions we decided it was the best for our son.”

However, the manner of Javier's birth was attacked by Spanish bishops and “pro-life” groups. A document published by the Spanish Bishops' Conference, the ruling body of the Roman Catholic Church, read: “You cannot kill one human being to save another.”

Manuel Cruz, director of the Life Foundation, said that the start of a new life was always good news, but added: “The method of this birth is degrading for human beings to have been selected like a prize.”

The law that permitted stem-cell research in Spain marked another clash between the Socialist Government and conservative church forces. The Church has opposed a series of liberal social reforms that the Government of José Luis Rodríguez Zapatero, the Prime Minister, has brought in since it came to power in 2004.

Mr Zapatero became a scourge of the right-wing hierarchy in the Church for legalising same-sex marriage, introducing fast-track divorce and making religious instruction an optional, rather than compulsory, subject in schools.

The two sides are set for more confrontations as the Socialists plan to reform Spanish abortion laws and may legalise a form of euthanasia. Cardinal Antonio Rouco Varela, the Archbishop of Madrid and president of the bishops' conference, is a renowned hardliner who will oppose any more reforms that offend Catholic morals.

Divide and cure

— Stem cells are unspecialised cells that are renewed for long periods through cell division

— When one cell divides, the two new cells produced can be developed into cells with specialised functions, like the beating cells of the heart muscle

— Stem-cell therapy will, scientists believe, eventually treat Parkinson's disease and spinal cord damage

Source: stemcell.nih.gov

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