Many scientists, Reed included, have addressed that second question. By carrying out painstaking cross-breeding experiments, and by working out where in the wings various genes are active, they identified a handful of pattern-defining genes, with colorful names like optix, doublesex, and cortex. “It was convincing but we didn’t know exactly what these genes were doing,” says Reed. Without the ability to delete the genes, and see if their absence changed the butterfly wings, “we didn’t have the final proof. There’s been this frustrating wall that I’ve banged my head against.”

CRISPR changed everything. This technique, used by bacteria for billions of years and harnessed by scientists in the last five, allows researchers to cut and edit DNA far more easily and precisely than ever before. As I’ve argued before, the oft-cited concerns that CRISPR will usher in a dystopic era of designer babies are overblown. But scientists are already exploiting it, to do experiments that would have been impossible a decade ago. They’ve used CRISPR to probe the weaknesses of cancer cells, study how bodies are built, and to learn how our feet evolved from fishy fins. And Reed has used it to finally do the gene-deleting experiments that had long eluded him.

By deleting the optix gene in a wide variety of butterflies, team member Linlin Zhang showed that red parts of the wing consistently turn black. The Gulf fritillary transforms from a vivid orange insect into a dark inky one. The small postman loses the vivid red streaks on its hind wings. And the painted lady loses its complex psychedelic patterns and becomes almost monochrome. “They just turn grayscale,” says Reed. “It makes these butterflies look like moths, which is pathetically embarrassing for them.”

These results reveal another side to CRISPR’s power: It’s so versatile that scientists can quickly manipulate the same genes in many species, including those that aren’t standard parts of laboratory life. For years, scientists have relied on a few handfuls of “model systems”—species that they can easily breed, study, and manipulate in laboratories. But CRISPR “fully unlocks butterflies as a model system,” says Wei Zhang from the University of Chicago, who published the first study that used the technique on butterflies.

These butterfly experiments reveal evolution’s penchant for both conformity and innovation. For example, optix does the same thing in species that have been separated by at least 80 million years of evolution. “It acts like a color/grayscale switch across the whole wing—quite incredible,” says Chris Jiggins from the University of Cambridge. But different species deploy it in different ways to produce their own distinctive patterns. If optix is a paintbrush, then other genes act as the painter’s hands, determining where the brush will go, and yet other genes act as the paints, determining which colors the brush eventually lays down. All of this can be easily rewired, producing a wide kaleidoscope of patterns from the same basic toolkit.