1. Topic 1 Introduction to the Study of Life
1.4 Classification
Biology 1001
September 16, 2005

2. 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

3. Figure 1.14 Classifying Life

4. 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

5. 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

6. Binomial Nomenclature
Attributable 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 coelebs
Ursus americanus 
EXAMPLES
 Homo sapiens with Felis catus
Homarus americanus 

7. Two Important Points About Classification
Classification is hierarchical
Classification reflects phylogeny

8. Classification of Kingdoms and Domains The 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

9. Classification of Kingdoms and Domains The Five-Kingdom System
Robert Whittaker proposed a system with five kingdoms
Monera, Protista, Plantae, Fungi, and Animalia
Plantae
Fungi
Animalia
Eukaryotes
Protista
Prokaryotes
Monera

10. Classification of Kingdoms and Domains The 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

11. 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

12. The Three Domain System of Classification

13. One Current View of Biological Diversity
Proteobacteria
Chlamydias
Spirochetes
Cyanobacteria
Gram-positive bacteria
Korarchaeotes
Euryarchaeotes, crenarchaeotes, nanoarchaeotes
Diplomonads, parabasalids
Euglenozoans
Alveolates (dinoflagellates, apicomplexans, ciliates)
Stramenopiles (water molds, diatoms, golden algae, brown algae)
Cercozoans, radiolarians
Red algae
Chlorophytes
Charophyceans
Domain Archaea
Domain Eukarya
Universal ancestor
Domain Bacteria
Chapter 27
Chapter 28

14. One Current View of Biological Diversity
Bryophytes (mosses, liverworts, hornworts)
Plants
Fungi
Animals
Seedless vascular plants (ferns)
Gymnosperms
Angiosperms
Amoebozoans (amoebas, slime molds)
Chytrids
Zygote fungi
Arbuscular mycorrhizal fungi
Sac fungi
Club fungi
Choanoflagellates
Sponges
Cnidarians (jellies, coral)
Bilaterally symmetrical animals (annelids,
arthropods, molluscs, echinoderms, vertebrates)
Chapter 29
Chapter 30
Chapter 28
Chapter 31
Chapter 32
Chapters 33, 34

15. Comparing Systems of Higher Level Classification
– A Study Aid
Click for Animation 