Claims that hundreds of bacterial genes have been transferred directly into humans are unfounded, according to a study published in June 21 Nature. The initial report by the International Human Genome Sequencing Consortium had revealed some surprising features. One of the most controversial findings was that at least 113 human genes appeared to have been inserted into the genome by horizontal transfer from bacteria.

Evolutionary geneticists were sceptical about the findings. They suspected this was technically unfeasible because horizontal gene transfer (HGT) is a principal force in genetic evolution and therefore rarely occurs between vastly distant species like bacteria and vertebrates. The only explanation for this degree of bacteria-vertebrate HGT was that it occurred in the germ line, which suggested the worrying possibility that bacterial infection or exposure to genetically modified organisms could result in gene transfer.

But, Michael Stanhope, James Brown and colleagues at GlaxoSmithKline in Pennsylvania have...