The genus *Heliconius* contains more than 40 species of brightly patterned butterflies. Researchers have investigated in the laboratory how one species, *Heliconius heurippa*, could have developed as a separate species. The phenotype of *H. heurippa* is intermediate between that of two other species, *H. cydno* and *H. melpomene*. Laboratory breeding experiments showed that: • matings between *H. cydno* and *H. melpomene* (parent species) produce fertile hybrid offspring • controlled matings of the hybrids produces individuals identical in appearance to *H. heurippa* within three generations • hybrid butterflies prefer to mate with each other, rather than with individuals of either of the parent species. The researchers concluded that the *H. heurippa* species could contain DNA from the two parent species as a result of hybridisation.