Scientists created a hypothesis that stated that the group of organisms currently in the order Struthioniformes should be classified differently from the other birds. Evidence for this hypothesis came from a study conducted by Haddrath and Baker (2001) who sequenced the mitochondrial DNA of a few different ratite species. After comparing the sequences of the various species within the ratites order, they concluded that the nucleotide sequence similarities in the data showed the relatedness of the DNA of the species, and that it differed from the DNA of other birds. Morphological data such as a lack of keel on the sternum of ratite species lends further support to this hypothesis. The similarities in DNA structure that are found between ratites support Darwin's theories of evolution as well, and are evidence that these species were once linked to another single species.