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Useful Reading
Campbell, Biology 6th Ed - Chapter 25, pgs 484-507
Campbell, Biology 7th Ed - Chapter 25, pgs 491-509
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There is a single phylogeny for all of life.Based on homologies seen in all life forms (e.g. nucleic acids, metabolic pathways), it is most parsimonious to conclude that all of life as we know it (currently and historically) shares a common ancestor. | |
Humans are a third chimpDNA homology suggests that humans are more closely related to living chimps than either are to other living primates.
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Birds are dinosaurs.Based on traits common with mammals (e.g. endothermy), it was long thought that birds were more closely related to mammals than to other vertebrates. When looking at various skull and hip characteristics, however, birds share more traits with certain lineages of dinosaurs. When evidence arose that some dinosaurs had beak-like traits and feathers, it became clear that these bird traits were all homologous with dinosaurs and that the clade of living birds was, in fact, within the clade of dinosaurs. | |
Origin of traitsPhylogenetics is used to identify where in a phylogeny traits first evolved. Once we have established an accurate phylogeny, we can make “tick marks” on a cladogram to indicate where a trait first appeared. These marks are usually placed on the branch before the MRCA of all taxa which share the trait. For example, we know that whales and their relatives (cetaceans) all have long, torpedo-shaped bodies. The closest relatives of cetaceans, the artiodactyls (e.g. cows, deer) do not have this body shape. Therefore, we know that this body shape must have arisen on the branch between the common ancestor of cetaceans and artiodactyls and the MRCA of all known cetaceans.
Review Questions |