Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Click to edit Master subtitle style 1/12/13 Chapter 4 The tree of life: how biologists use phylogeny to reconstruct the deep past1/12/13 Darwin viewed evolution as a branching process“As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications.” – Darwin, 18591/12/13 Phylogeny: A visual representation of the evolutionary history of populations, genes, or species.1/12/13 A phylogeny is similar to a family tree1/12/13 Reading a phylogenetic treeTaxa can be rotated around nodes and still depict the same relationships1/12/13 Phylogenies may be drawn in different styles1/12/13 No currently existing species is ancestral to any other1/12/13 Trees can be drawn with fewer species1/12/13 Life is organized in a nested hierarchy1/12/13 Taxonomic units legitimate only if they represent a cladeClades are monophyletic groups1/12/13 Some Linnean classifications are not monophyletic1/12/13 Key Concepts•New lines of evidence suggest some commonly used taxon names should be revised to reflect evolutionary history1/12/13 Reconstruction of phylogenies is based on analysis of characters1/12/13 Clades are determined by synapomorphies1/12/13 Not all traits are similar due to common descent•Homoplasy: character state similarity not due to common descent–Convergent evolution: independent evolution of similar trait–Evolutionary reversals: reversion back to an ancestral character state1/12/13 Homoplasious traits can be misleading in reconstruction of phylogenies1/12/13 Principle of parsimony used to find tree that is most likely to be correct1/12/13 Key Concepts•Phylogenies are created by identifying synapomorphies•Homoplasy can create the mistaken impression that two species are closely related when they are not1/12/13 Fossils can be used to constrain divergence times1/12/13 Fins to limbs: homology through timeCoelacanths are one of the closest living relatives of tetrapods1/12/13 Coelacanth fins are homologous to tetrapod forelimbFossil record should document transition from fins to forelimbs1/12/13 Phylogenies generate hypotheses1/12/13 Scientists predicted where transitional fossils would be found•Searched mid-Devonian rocks in Northern Canada–Appropriate age and habitat1/12/13 Tiktaalik: transitional fossil between fish and tetrapods1/12/13 Tiktaalik forelimbs share more homologies with tetrapods1/12/13 Phylogeny reveals how tetrapod traits evolved over time1/12/13 Homology can be obvious…or notHomology between human (top) and chimpanzee (bottom) hands is obviousBut, what reptilian bones are homologous to mammalian inner ear bones?1/12/13 Fossils and phylogeny document transition of bones from jaw to ear1/12/13 Birds are dinosaurs: tracking the evolution of feathers and flightArchaeopteryx, discovered in 1860, dates to 145 mya1/12/13 Feathers evolved before flight1/12/13 Feathers originally involved in other functionsExaptation: natural selection co-opts a trait for a new function1/12/13 Feather attachments on Velociraptor bones1/12/13 Dinosaur nesting behavior1/12/13 Darwin proposed that humans most closely related to African apes•Fossil record should document transition to to unique human traits–Bipedality–Larger brain size–Smaller canine teeth1/12/13 Phylogeny reveals transitions1/12/13 Transition to bipedality•Appears to have evolved before larger brain–Position of foramen magnum–Weight bearing stance–Short, stiff toes1/12/13 Ardipithecus adapted to walking and arboreal life1/12/13 Hominins became better adapted to walking upright over timeTracks made by Australopithecus afarensis (1.5 myo)Homo erectus (~2 myo)1/12/13 Key Concepts•Living members of a clade may not reliably indicate origins of synapomorphies•The mammalian inner ear is made up of modified parts of the jaw•Feathers are an exaptation•Our current understanding of human evolution is based on many specimens of 20 different species•Bipedalism evolved before large brain