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PHYLOGENY and the TREE of LIFE. Chapter 26. Phylogeny and Systematics. Phylogeny -- Evolutionary history of a species or group of related species; attempts to trace macroevolution.

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PHYLOGENY and the TREE of LIFE

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Phylogeny and the tree of life l.jpg

PHYLOGENY and the TREE of LIFE

Chapter 26


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Phylogeny and Systematics

  • Phylogeny -- Evolutionary history of a species or group of related species; attempts to trace macroevolution.

  • Macroevolution – Origins of broader groups of organisms; studied in relation to major events of environmental change.

  • Systematics -- Study of biological diversity in an evolutionary context.

  • Current biological diversity reflects past episodes of speciation and macroevolution.

  • Taxonomy – Component of systematics which includes identification and classification of species.


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Taxonomy and Classification

  • System used today was developed by Carl Linnaeus in the 18th century.

  • Two main features: 1) sort and name separate species, and 2) organize them into categories based on relationships.

  • Binomial nomenclature:Two-part Latin name unique to each species.

  • Ex: Genus Felis includes many species of related organisms (cats).

  • Species Felis silvestris; Felis lynx; Felis leo.


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Broader categories of classification

  • Kingdom

  • Phylum (phyla, plural)

  • Class

  • Order

  • Family

  • Genus (genera, pl)

  • Species

  • Animalia

  • Chordata

  • Mammalia

  • Carnivora

  • Canidae

  • Canis

  • Canis familiaris


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Kingdoms

  • 5 kingdom system

  • Monera (bacteria)

  • Protista (algae and protozoans)

  • Fungi

  • Plantae

  • Animalia

  • 6 kingdom system

  • Archaebacteria

  • Eubacteria

  • Protista

  • Fungi

  • Plantae

  • Animalia


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Tools of Taxonomy

  • Outward similarities; embryonic development; life cycle stages.

  • Homology – similarities due to common ancestry.

  • But superficial features don’t always reflect evolutionary relationships.

  • Analogy -- Similarities due to convergent evolution, not common ancestry.

  • Convergent evolution -- Similar characteristics due to sharing similar ecological roles; natural selection shapes adaptations.


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Homologous Structures


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Convergent Evolution


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Other Methods

  • Phenetics: makes no evolutionary assumptions.

  • Comparison is made of as many phenotypes as possible.

  • If enough characteristics are compared, homology will overshadow analogy.(?)

  • Overall phenotypic similarity is not a reliable indicator of phylogeny.(?)

  • This may be more useful for analyzing DNA sequence data.


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Phenetics


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DNA Sequencing


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Other Methods continued

  • Cladistics: classifies organisms according to phylogeny.

  • Cladogram -- a branching “family tree”.

  • Each species in the cladogram has a mixture of primitive characters that existed in the common ancestor and characters that evolved more recently.

  • A major difficulty in cladistics is finding appropriate categories for each branch point.


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Cladogram


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