For 150 years scientists have been trying to explain convergent evolution. One of the best-known examples of this is how poisonous butterflies from different species evolve to mimic each other’s color patterns — in effect joining forces to warn predators, “Don’t eat us,” while spreading the cost of this lesson. New research has solved part of the mystery by identifying a single gene called optix responsible for red wing color patterns in a wide variety of passion vine butterfly species.