Chapter 18 Systematics Seeking Order Amidst Diversity Lecture Outlines by Gregory Ahearn University of North Florida Copyright 2011 Pearson Education Inc Chapter 18 At a Glance 18 1 How Are Organisms Named and Classified 18 2 What Are the Domains of Life 18 3 Why Do Classifications Change 18 4 How Many Species Exist Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 1 How Are Organisms Named and Classified The branch of biology that is concerned with naming and classifying organisms is known as taxonomy Modern taxonomy was est by the swedish naturalist Carl von Linne 1707 1778 Called himself Carolus Linnaeus Linnaeus introduced the two part scientific name to all organisms Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 1 How Are Organisms Named and Classified The two part scientific name of an organism is formed from the genus and species A genus is a group that includes a number of very closely related species A species within a genus includes populations of organisms that can potentially interbreed under natural conditions The genus Sialia bluebirds includes three species Sialia sialis eastern bluebird Sialia Mexicana western bluebird Sialia Currocoides mountain bluebird Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 1 How Are Organisms Named and Classified Each two part scientific name is unique and recognized worldwide Scientific names are always underlined or italicized The first letter of the genus name is always The first letter of the species name is always The species name is always paired with its capitalized lowercase genus name Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 1 How Are Organisms Named and Classified Classification originated as a hierarchy of categories Each species was placed in a series of hierarchically arranged categories on the basis of resemblance to other species Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 1 How Are Organisms Named and Classified The Linnaean classification system came to include eight major categories or taxonomic ranks Domain Kingdom Phylum Class Order Family Genus species Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 1 How Are Organisms Named and Classified Modern classification emphasizes patterns of evolutionary descent In 1859 Charles Darwin 1809 1882 published On the Origin of Species This work demonstrated that all life is related to common ancestry Biologists then realized that taxonomic categories should reflect evolutionary relatedness The more categories two organisms share the closer their evolutionary relationship Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 1 How Are Organisms Named and Classified Modern classification emphasizes patterns of evolutionary descent continued Today the process of classification focuses on reconstructing phylogeny or evolutionary history The science of reconstructing phylogeny is known as systematics Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 1 How Are Organisms Named and Classified Modern classification emphasizes patterns of evolutionary descent continued Systematists have increasingly focused their efforts on building evolutionary trees rather than dividing organisms into specific Linnaen classifications Systematists name groups which they call clades that include species linked by descent from a common ancestor Clades can be arranged in a hierarchy with smaller clades nested within larger ones Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 1 How Are Organisms Named and Classified Systematists identify features that reveal evolutionary relationships All organisms share certain similarities Biologists look at many kinds of characteristics in the search for informative similarities Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 1 How Are Organisms Named and Classified Anatomy plays a key role in systematics Historically the most important and useful distinguishing characteristics have been anatomical Systematics look carefully at similarities in both the external body structures such as skeletons and muscles Homologous structures such as the finger bones of dolphins bats seals and humans provide evidence of a common ancestor Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 1 How Are Organisms Named and Classified Anatomy plays a key role in systematics continued Systematists examine microscopic similarities to discern finer details Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 1 How Are Organisms Named and Classified Molecular similarities are also useful for reconstructing phylogeny Systematists examine genetic similarities between DNA nucleotide sequences It has been estimated that 96 of the chimpanzee genome is identical with that of humans Similarities in chromosome structure also can be used to establish relationships between organisms Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 2 What Are the Domains of Life Before 1970 systematists divided all species into two groups Animalia plantae As knowledge expanded of life s evolutionary relationships it became clear that a two domain approach was an oversimplification Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 2 What Are the Domains of Life A three domain system more accurately reflects life s history Carl Woese laid the groundwork He discovered that prokaryotic organisms included two very distinct groups Bacteria and Archaea on the basis of their respective nucleotide sequences of ribosomal RNA Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 2 What Are the Domains of Life A three domain system more accurately reflects life s history continued Within the domain Eukarya there are four different groups of organisms Animalia animals Plantae plants Fungi fungi Protists eukaryotic organisms that are not animals plants or fungi Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 18 3 Why Do Classifications Change Species designations change when new information is discovered Systematic changes at the top levels of classification occur only rarely but there are regular changes in species level It was previously thought that there were only two species of elephant African and Indian More recently the African elephant species has been divided into two species the savannah elephant and the forest elephant Genetically these two African species have no more in
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