2. 12.1 The Invention of the Linnaean System
To name organisms, biologists use a multilevel grouping of individuals called classification
Organisms were first classified more than 2,000 years ago by Aristotle
Living things were either plants or animals
Later groups started to be formed and referred to as genera (singular genus)

3. The classification system of the Middle Ages was known as the polynomial system
Polynomials were a string of Latin words or phrases consisting of up to 12 or more words
This system was cumbersome and confusing
In the 1750s, the Swedish biologist Carolus Linnaeus developed the binomial system
Binomials are two-part names
They have become our standard way of designating species

4. Fig. 12.1 How Linnaeus named two species of oaks

5. 12.2 Species Names
A group of organisms at a particular level in a classification system is called a taxon (plural, taxa)
Taxonomy is the branch of biology that identifies and names organisms
Organisms are named using Latin and in such a way that no two have the same name
Using common names can be misleading

6. Fig. 12.2 Common names make poor labels
Bears
Robins
Corn

7. 12.2 Species Names By convention, the binomial name consists Genus
The first word and is always capitalized
Epithet
The second word which refers to the species and is not capitalized
The two words are written in italics
Together, they form the scientific name
Example: Apis mellifera
The honeybee

8. Information gets more and more general
12.3 Higher Categories
Taxonomists use a hierarchical system to classify organisms
spaghetti
green
for
over
came
Philip
King
Species
Genus
Family
Order
Class
Phylum
Kingdom
Information gets more and more general

9. Fig. 12.3

10. 12.4 What Is a Species? John Ray (about 1700)
A species is a group of individuals that can breed with one another and produce fertile offspring
Fig. 12.4
Sterile

11. 12.4 What Is a Species? Ernst Mayr (1940s)
Proposed the biological species concept
Species are groups that are reproductively-isolated
This concept works well for animals, but poorly for other organisms
Problems
Assumes regular outcrossing
Assumes strong reproductive barriers

12. 12.4 What Is a Species?
Since the time of Linnaeus, about 1.5 million species have been named
However, scientists estimate that at least 10 million species exist
At least two-thirds of these occur in the tropics

13. 12.5 How to Build a Family Tree
Taxonomy also enables us to glimpse the evolutionary history of life on earth
The evolutionary history of an organism and its relationship to other species is called phylogeny
The reconstruction and study of phylogenetic trees is called systematics

14. 12.5 How to Build a Family Tree
A clade is a group of organisms related by descent
Cladistics is the construction of phylogeny based on similarities derived from a common ancestor
Examination of these derived characters allows the construction of a branching cladogram
Cladograms are not true family trees
They convey comparative relationship information
Each cladogram must contain an outgroup to which the ingroup is compared

15. Fig. 12.5 A cladogram of vertebrate animals
Ingroup
Outgroup

16. 12.5 How to Build a Family Tree
Modern cladistics attempts to assign extra weight to the evolutionary significance of key characters
Weighting characters lies at the heart of traditional taxonomy
Phylogenies are constructed based on a large amount of information about the organism gathered over the years
To construct their trees traditional taxonomists use both ancestral and derived characters
Cladists use only derived characters

17. Fig. 12.6 Two ways to classify terrestrial vertebrates
Birds have their own Class
Birds are lumped with reptiles

18. 12.5 How to Build a Family Tree
So which approach is better?
Traditional taxonomy, when a lot of information is available to guide character weighting
Cladistics, when little information is available about how the character affects the life of the organism

19. Fig The cat family tree

20. Fig The cat family tree

21. 12.6 The Kingdoms of Life
The designation of kingdoms has changed over the years
Originally there were only two kingdoms
As more information about organisms was obtained, the number of kingdoms increased!
Indeed, a taxonomic level higher than kingdom has been recognized
Domain

22. 12.6 The Kingdoms of Life
Fig Different approaches to classifying living organisms

23. More closely related to each other than either is to bacteria
Fig A tree of life
More closely related to each other than either is to bacteria

24. 12.7 Domain Archaea Consists of only one kingdom, the Archaebacteria
Archaebacteria inhabit some of the most extreme environments on earth
They share certain key characteristics
Cell walls lacking peptidoglycan
Unusual lipids and unique rRNA sequences
Some archaebacterial genes possess introns

25. Archaebacteria are grouped into three general categories Methanogens
Obtain energy by using hydrogen gas to reduce carbon dioxide to methane gas
Extremophiles
Grow under extreme conditions
Thermophiles (heat)
Halophiles (salt)
pH-tolerant
Pressure-tolerant
Nonextreme archaebacteria
Grow in the same environments as bacteria do

26. 12.8 Domain Bacteria Consists of only one kingdom, Bacteria
Bacteria are the most abundant organisms on earth
They play critical roles throughout the biosphere
Most taxonomists recognize major groups
Bacteria are as different from archaebacteria as they are from eukaryotes

27. 12.9 Domain Eukarya Appeared about 1.5 billion years ago
Consists of four kingdoms
Animalia
Plantae
Fungi
Protista
Well defined evolutionary groups
Largely muticellular
Very diverse
Unicellular

28. TABLE 12.2

29. TABLE 12.2

30. 12.9 Domain Eukarya
The hallmark of eukaryotes is complex cellular organization
This is highlighted by the presence of organelles
Mitochondria and chloroplasts most likely entered early eukaryotic cells by endosymbiosis
Mitochondria are descendants of purple bacteria
Chloroplasts are descendants of cyanobacteria

31. Fig. 12.10 Diagram of the evolutionary relationship among the six kingdoms
Symbiotic events

32. Interestingly, other types of photosynthetic protists are endosymbionts of some eukaryotic organisms
Zooxanthellae algae
Fig
Coral animal