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Download Descent with Modification: A Darwinian View of Life
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Relatedness of Organisms Cladistics and Phylogeny Ways of Relating Organisms • Traditional schemes for classifying organisms were based on morphological comparisons. • Molecular phylogenetics has enhanced and/or superceded traditional approaches in the last 30 years. Molecular Phylogenetics • DNA, RNA and proteins are compared to establish evolutionary relationships • A new prokaryote domain (kingdom) called Archaea has been established to account for profound molecular differences • The origins of eukaryotes have been clarified using commonality of genetic code Cladograms • Cladograms group species according to their most recent common ancestor on the basis of shared characteristics. Cladograms We’re cousins! A Cladogram is a graphed phylogeny-a depiction of evolutionary relationships Tree Types Evolutionary trees measure time. Phylograms measure change. sharks sharks seahorses Root frogs owls 50 million years crocodiles armadillos bats seahorses frogs owls Root crocodiles armadillos 5% change bats Relatedness of All Cellular Organisms Relatedness of All Eukaryotes Relatedness of All Plants Relatedness of All Fungi Relatedness of All Animals Homologies: Vertebrate Forelimbs “Surely, the best way to construct the infrastructure of a bat’s wing is not also the best way to build a whale’s flipper.” p. 439, Campbell & Reece, 2002 Homologies: Vertebrate Embryos Homologous structures are not necessarily useful to a recipient organism A homologous structure is simply an anatomical (i.e., structural) characteristic that serves as a homology Molecular Homologies Vestigial Structures Vestigial Structures Vestigial structures are a kind of homology, the persistence of a feature, though one which is no longer (terribly) useful to its owner Paleo Homology (whale legs) A homology, one shared with other tetrapods, and one that is not vestigial More on Whale Evolution A structure that is expensive to make or to sustain, but which makes little positive impact on survival or reproductive success will not be selected for (indeed, may be selected against) and therefore ultimately may be lost via evolution (i.e., via natural selection or via genetic drift) Developmental Error The genes for tail formation presumably are still with us, just not normally expressed (that is, they are vestigial). Convergent Evolution Analogies are products of convergent evolution The Fossil Record
