Chapter 18Classification

18.1 Finding Order in Diversity SC.912.L.15.4 and SC.912.N.1.1

Assigning Scientific NamesKey Question: What are the goals of binominal nomenclature and systematics? The first step in understanding and

studying diversity is to describe and name each species.

In the eighteenth century, European scientist agreed to assign Latin or Greek names to each species.

Binomial Nomenclature Binomial nomenclature is a two part

scientific name given to a species. For example, the polar bear’s binomial

nomenclature is Ursus maritimus. Ursus is the genus of the organism and maritimus is the species.

Classifying Species Into Larger Groups The goal of systematics is to organize

living things into groups that have biological meaning.

They group species into larger groups with organisms that are similar to them.

The Linnaean Classification SystemKey Question: How did Linnaeus group species into larger taxa? Over time, Linnaeus’ original

classification system expanded to include seven hierarchical taxa: species, genus, family, order, class, phylum, and kingdom.

Organisms are grouped by their characteristics within each taxa.

Problems with Traditional Classification Systematics over time have emphasized

a variety of characteristics, and some of these groups have been defined differently.

Sometimes problems come about when species are classified by observable traits.

18.2 Modern Evolutionary Classification SC.912.L.15.5, SC.912.N.1.1, SC.912.L.15.4

Evolutionary ClassificationKey Question: What is the goal of evolutionary classification? The goal of phylogenetic systematics, or

evolutionary classification, is to group species into larger categories that reflect lines of evolutionary descent, rather than overall similarities and differences.

Phylogeny is the evolutionary history of lineages.

Common Ancestors Phylogenetic systematics places

organisms into higher taxa whose members are closely related to another member of the taxa.

In the past, all members in a large taxon shared a common ancestry and is true to even the largest taxa.

Clades Classifying organisms according to the

rules places them into groups called clades.

A clade has to be a monophyletic group which includes a single common ancestor and all of its descendants.

CladogramsKey Question: What is a cladogram? A cladogram links groups of organisms

by showing how evolutionary lines, or lineages, branch off from common ancestors.

Cladistic analysis compares carefully selected traits to determine the order in which groups of organisms branch off their common ancestors.

Building Cladograms A speciation event, where one ancestral

species splits into two new ones, and creates two branch points.

The node represents the last point at which the two lineages shared a common ancestor.

Derived Characters A derived character is a trait that arose

in the most recent common ancestor of a particular lineage and was passed along to its descendants.

Whether or not a character is derived depends on the level at which the organisms are grouped.

Losing Traits Somewhere in a lineage there is a trait

that can be lost. For example, snakes lost the trait of having four legs.

Interpreting Cladograms The lowest node represents the last

common ancestor of the group being represented.

Then each new node is a derived characteristic of the specie.

Clades and Traditional Taxonomic Groups True clades must be monophyletic,

which means that it contains an ancestral species and all of its descendants.

Some groups do not form valid clades.

DNA in Classification Key Question: How are DNA sequences used in classification? Some organisms are similar but have no

physical similarities. DNA can be used to show the common

ancestor between two species.

Genes as Derived Characters The more derived genetic

characteristics two species share, the more recently they shared a common ancestor and the more closely they are related in evolutionary terms.

Genetic information is stored in DNA, it can be used to trace back to previous generation or lineages.

New Techniques Suggest New Trees The use of DNA characteristics in

cladistic analysis has helped to make evolutionary trees more accurate.

Scientists use DNA evidence when anatomical traits alone can’t be provide clear answers.

18.3 Building the Tree of Life SC.912.L.15.6, SC.912.N.1.1, SC.912.N.1.6, SC.912.L.15.4, SC.912.L.15.5, MA.912.S.3.2

Changing Ideas About KingdomsKey Question: What are the six kingdoms of life as they are now identified? During Linnaeus’ time, the only known

difference among living things were the fundamental characteristics that separated animals from plants.

In time, biologist learned more about the natural world, and they realized that Linnaeus’ two kingdoms did not reflect the full diversity of life.

Five Kingdoms When researchers began to study

microorganisms, they discovered that single celled organisms were completely different from plants and animals, and were placed in a new kingdom called Protista.

Yeasts and molds, along with mushrooms went into their own kingdom known as Fungi.

Bacteria was also put into a new kingdom called Monera.

Six Kingdoms In the 1990s, researchers learned more

about genetics and biochemistry of bacteria, and made it clear that the kingdom Monera was actually made up of two genetically and biochemically different groups.

The six kingdom system of classification includes the kingdoms Eubacteria, Archaebacteria, Protista, Fungi, Plantae, and Animalia.

Three Domains A domain is a larger, more inclusive

category than a kingdom. There are three domains: Domain

Bacteria, corresponding with kingdom Eubacteria, Domain Archaea, corresponding with kingdom Archaebacteria, and Domain Eukarya, corresponding with kingdom Fungi, Plantae, Animalia, and Protista.

The Tree of All LifeKey Question: What does the tree of life show? Cladograms are visual presentations of

hypotheses about relationships. The tree of life shows current

hypotheses regarding evolutionary relationships among the taxa within the three domains of life.

Domain Bacteria The members in this domain have to be

unicellular and prokaryotic. This domain corresponds with the

kingdom Eubacteria.

Domain Archaea Members of this domain are unicellular

and prokaryotic, but live in extreme conditions.

For example, in a volcano or on mount Everest.

Domain Eukarya Members of this domain are

multicellular and eukaryotic. This domain consists of four of the

major kingdoms of the six-kingdom system: Protists, Fungi, Plantae, and Animalia.