Diploid vertebrates have two sets of chromosomes, one from each parent. In contrast, polyploidy, meaning to possess three or more sets of chromosomes, is very rare in animals. To find out how new vertebrate species have evolved, and, more generally, how the current biodiversity emerged, evolutionary biologists are studying green toads (Bufo viridis), an excellent model system for studying evolutionary processes, because they can be diploid or polyploid.