Topic 1Introduction to the Study of Life

1.4 Classification

Biology 1001September 16, 2005

The Basic Concept of Grouping

• A natural human tendency is to group diverse items according to similarities

• Taxonomy is the branch of biology that names and classifies biological organisms

• Formalizes ordering of organisms into a series of increasingly comprehensive groups

Figure 1.14 Classifying Life

THE Biological Species Concept

• The species is the “unit” of organization of biological diversity– “Species” is Latin for “kind” or “appearance”– Species are usually morphologically distinct entities– The primary definition of species is the biological species

concept attributable to Mayr (1942)

• The biological species concept defines a species as “a population or group of populations whose members have the potential to interbreed in nature to produce viable, fertile offspring”

• Species are reproductively isolated from other species

Other Species Concepts

• Morphological species concept– Differentiate species by their form (size, shape etc.)

• Paleontological species concept– Describes morphological species known only from fossil record

• Ecological species concept– Views species in terms of role or niche in community

• Phylogenetic species concept– Defines species as branches on a tree of life

Concepts that emphasize unity; are useful in certain situations

Binomial NomenclatureAttributable to Carolus Linnaeus1 and Systema naturae (1748)

• A two-part, Latinized, scientific1,2 name called the binomial

• The first part is the genus, the second is the specific epithet

• The genus is capitalized, the specific epithet is not

• Both parts are italicized (or underlined)

Fringilla coelebsUrsus americanus

Homo sapiens with Felis catusHomarus americanus

EXAMPLES

Two Important Points About Classification

Classification is hierarchical

Classification reflects phylogeny

Classification of Kingdoms and DomainsThe Two-Kingdom System

Early classification systems had two kingdoms

Dates to Linnaeus who divided the world into plants and animals (and rocks!)

Based on macroscopic features such as motility

Grouped together unrelated organisms – plants, fungi, and bacteria were all placed in the plant kingdom

Classification of Kingdoms and DomainsThe Five-Kingdom System

• Robert Whittaker proposed a system with five kingdoms

– Monera, Protista, Plantae, Fungi, and Animalia

Plantae Fungi Animalia

Protista

Monera

Eukaryo

tes

Prokaryotes

Classification of Kingdoms and DomainsThe Downfall of the 5K System

• The 5K System is not a natural construct

• Problems with the 5K system- Monera contains two distinct evolutionary lineages- Protista is a “dumping ground” containing many unrelated

lineages

• Neither of these kingdoms represents phylogeny (evolutionary history)

• Based on new data, biologists now recognize three major evolutionary lineages of life – the three domains

The Three Domain System

• The three domain system recognizes evolutionary relationships

– Replaces the five kingdom system

– Includes the domains Archaea, Bacteria, and Eukarya

– Superkingdoms, a taxonomic level higher than kingdom

• Each domain is split into one or more kingdoms

– Note that Monera and Protista are now obsolete kingdoms

– The number of kingdoms in the domains is still a matter for scientific inquiry

The Three Domain System of Classification

One Current View of Biological DiversityP

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Domain Archaea Domain Eukarya

Universal ancestor

Domain Bacteria

Chapter 27 Chapter 28

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Chapter 29 Chapter 30 Chapter 28 Chapter 31 Chapter 32 Chapters 33, 34

One Current View of Biological Diversity

Comparing Systems of Higher Level Classification – A Study Aid

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