The discovery of the myriad little deaths which lead to life brought the most coveted prize in world medicine to two Britons and an American yesterday.

Sir John Sulston, Sydney Brenner and Robert Horvitz were awarded the Nobel prize for medicine for decades of collective work studying the genesis and growth of microscopic beasts called nematode worms.

Their research showed that the growth and, equally important, the programmed death of the hundreds of cells in the developing worm was a key to understanding the same processes in the multi-trillion celled human body.

The award to Sir John, now 60, is bound to be seen as at least a nod towards his leading role in decoding the "book of life", the human genome, the work for which he is better known to the public.

There is no mention of this in the citation, however, and he was only one of a number of scientists who led the publicly funded human genome project. The award of science Nobel prizes tends to lag decades behind the discoveries for which they are awarded.

Nonetheless, Sir John yesterday linked the "sharing" spirit of the worm work to that of the public genome project, both freely accessible to all scientists, unlike the rival, commercial genome project.

"It's tremendously exciting for me," he said. "The worm worked so well because the community held an ethos of sharing - just as the public genome projects have - from the beginning. We gave all our results to others as soon as we had them. From sharing, discovery is accelerated in the community. Research is hastened when people share results freely."

Apart from immense prestige, the three scientists share a prize of 10m Swedish krona, about £700,000.

Sydney Brenner, 75, was born in South Africa and is now based at the Molecular Sciences Institute in Berkeley, California, but is a British citizen who spent most of his working life at the Medical Research Council in Cambridge. Sir John and Mr Horvitz both worked under him for part of their careers.

In 1974 he showed how the growth of life from a single cell to a whole creature could be tracked by watching the effects of genetic mutations in the transparent, millimetre-long nematode.

Sir John, who is based at the Wellcome Trust Sanger Institute in Cambridge, built on Mr Brenner's work to reveal how every worm grows in the same way, its cells unfolding and dying in a predetermined genetic sequence, like clockwork.

Ten years later Robert Horvitz, 55, whose lab is at the Massachusetts Institute of Technology, identified the first so-called "death genes", necessary to prompt unneeded cells to commit suicide.

As a result, we now know that the cell death mechanism is astonishingly similar in the primitive worms and human beings, making the creatures an ideal tool to understand human development and disease. There are hopes that one day it will be routine to send a targeted chemical command to cancer cells, ordering them to kill themselves.

The prizewinners, who will receive their awards in December, are picked by the Nobel Assembly at the Karolinska Institute in Sweden, on the basis of mainly secret nominations by previous laureates and leading scientists around the world.

This is the second year running that the medicine prize has gone to two Britons and an American. Timothy Hunt and Paul Nurse won with Leland Hartwell of the US last year.

Lord May of Oxford, the president of the Royal Society, said yesterday that Mr Brenner was being recognised for a "lifetime of outstanding contributions to science... It has long been recognised within the scientific community that Sydney Brenner's work has had an extraordinarily profound impact."

He added: "John Sulston, one of Sydney Brenner's many proteges, has demonstrated world-class leadership, not just in his science but also as head of the UK's contribution to the human genome project. He is a great role model for future generations of researchers, and has demonstrated great foresight in tackling the ethical, as well as scientific, consequences of one of the greatest scientific endeavours of all time."

Other Nobel prizes will be announced this week - physics today, chemistry and economics on Wednesday, literature probably on Thursday, and peace on Friday.