For decades, biology textbooks have enshrined a simple rule: DNA is made by copying a template. After one enzyme unzips a DNA double helix into separate strands, another called a polymerase builds a complementary sequence, base by base, for each strand. Presto: two copies of the original DNA. But new research into how bacteria defend themselves from viruses now shows this synthesis rule isn’t absolute. Now, a team describes a bacterial enzyme that synthesizes DNA without a nucleic acid template, using its own structure as a guide. Learn more: scim.ag/4tN5TBR