How much of your DNA actually does something useful? Of the 3 billion letters that make up your genome, we know that only 1.5 percent consists of genes, which carry the instructions for making proteins. Of the remaining 98.5 percent, some sequences affect how, when and where our genes are used, but the vast majority have no obvious roles. They contain the corpses of dead genes, parasitic strings of selfish DNA that have run amok, and other bits that seem to do nothing. You might call them junk.

So, what would happen if you got rid of it? If you stripped all these “non-coding” sequences from the human genome, would you still get a normal, living person? This experiment will always