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.