Bisher hat man angenommen, alle Laufvögel (Ratiten; z. B. Emus und Kiwis) stammten von einem gemeinsamen Vorfahren ab. Doch neue Untersuchungen haben ergeben, dass die Laufvögel und damit die Flugunfähigkeit mit den dazugehörigen Anpassungen mindestens dreimal unabhängig voneinander entstanden sind.
Mir hat besonders die Conclusion des Artikels gefallen, in dem dieser Befund veröffentlicht wurde:
Exhaustive analyses of DNA sequence data from 20 unlinked nuclear genes provide strong evidence that ratites are polyphyletic. We have discovered a robust genome-wide signal that is not associated with any known phylogenetic artifact. We believe this phylogeny resolves a debate on ratite origins that began in the time of Huxley and Owen. Our phylogeny implies that the numerous striking similarities associated with flightlessness had independent origins in various ratite lineages. Thus, the flightless ratites are living evidence of parallel evolutionary trajectories from flighted ancestors. The possibility that multiple, unique developmental genetic pathways underlie the ratite form should be tested in light of this new phylogenetic hypothesis. Finally, our phylogeny removes the need to postulate vicariance by continental drift to explain ratite distribution. Although that theory seemed to represent a consilience between evolutionary biology and geology, it was never completely consistent either with any published phylogeny or the existence of paleognath fossils in the Northern hemisphere. Perhaps the impact of our phylogeny should be viewed as yet another example of the phenomenon that Huxley called “the great tragedy of science—the slaying of a beautiful theory by an ugly fact.”[Quelle: Harshman et al. (2008). Phylogenomic evidence for multiple losses of flight in ratite birds. PNAS 105(36): 13462-13467]
Science, I like it.