Mice born without large portions of their “junk DNA” seem to survive normally. The result contradicts the beliefs of many scientists who have sought to uncover the function of these parts of the genome.

David Haussler of the University of California, Santa Cruz, who has investigated why genetic regions are conserved, believes that non-coding regions may have an effect too subtle to be picked up in the tests to far.

“Survival in the laboratory for a generation or two is not the same as successful competition in the wild for millions of years,” he argues. “Darwinian selection is a tougher test.”