Picky females play a critical role in the survival and diversity of species, according to a new study. To date, biodiversity theories have focused on the role played by adaptations to the environment: the species best equipped to cope with a habitat would win out, while others would gradually go extinct. The new study presents the first theoretical model demonstrating that selective mating alone can promote the long-term coexistence of species — such as frogs, crickets, grasshoppers and fish — that share the same ecological adaptations and readily interbreed.