FOR most people, the idea of isolation is an uncomfortable one. It interests Paul Turner, however, because it goes hand in hand with the formation of new species. Dr Turner is a biologist at Yale University, and he and his team have just become the first people to create a new biological species in a laboratory by encouraging the sort of ecological isolation that happens in the wild. Admittedly the species in question is a virus, but the proof of principle is important. Moreover, Dr Turner's method might be adapted to examine how animal viruses jump the species barrier to become agents of human disease.

One definition of a species is a group of organisms whose members can breed with each other but not with outsiders. Such groups can form in several ways. One is that a species splits into groups that adapt to different foodstuffs. If those foodstuffs live in different places, the groups will never meet. Since they no longer meet, they no longer interbreed. They have thus become ecologically isolated and natural selection can then drive their genetic make-ups apart.

It has been a source of disappointment to researchers into evolution that although they can replicate the effects of natural selection on individual traits (for example, resistance to pesticides or changes in behaviour), no one has managed to evolve a new species this way. Laboratory species have been created only by the isolating effects of hybridisation. Speciation by hybridisation does happen in the wild, but is exceptional.

As they report in Evolution, Dr Turner and his team performed their trick with a type of virus called a bacteriophage. As their name suggests, these infect bacteria. Those the team study can live in more than one bacterial species.

The normal versions of Dr Turner's phages are able to parasitise four types of bacteria. He and his team, however, found a mutant that could infect two additional species. They cultivated a population of this mutant in one of the newly available species and found that after 15 days it had adapted to its new host so well that it had lost the ability to infect other bacteria. It had thus become effectively isolated, because it could never hook up with individuals from other strains. It could therefore be considered a new species.

Bacteria are not people, of course. Neither are phages retroviruses. But what Dr Turner has done is logically equivalent to the step taken by, for example, one particular chimpanzee retrovirus when it leapt to humans and evolved into what is now known as HIV. By showing that viruses can evolve into new species this way in the laboratory, Dr Turner may thus have invented a tool with medical applications. And he has certainly given a psychological boost to evolutionary biologists.