1. The Tree of Life

2. Why Classify? We classify to make organisms easier to study.
To study the diversity of life, biologists use a classification system to name organisms and group them in a logical manner.
The field of taxonomy allows scientists to classify organisms and assign each organism a universally accepted name in order to study the diversity of life.

3. Linnaeus’s System of Classification
During the eighteenth century, Swedish botanist Carolus Linnaeus developed a two-word naming system called binomial nomenclature
Linnaeus often classified organisms based on similarities in structures and details of anatomy

4. Binomial Nomenclature
In binomial nomenclature, each species is assigned a 2-part Latin name
The name is always written in italics with the 1st word is always capitilized
Example: Homo sapiens (humans)
The 1st part of the name is the genus and the second part of the name is unique to each species within that genus

5. Linnaeus’s System of Classification
Linnaeus’s system of classification uses 7 taxonomic categories (from largest to smallest):
Kingdom – largest & most inclusive
Phylum – includes many different organisms that share important characteristics
Class – composed of similar orders
Order – composed of similar families
Family – genera that share many characteristics
Genus – a group of closely related species
Species – a group of individuals so similar that they can breed and produce fit offspring

6. Human Classification Kingdom: Anamalia Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Primates
Family: Hominidae
Genus: Homo
Species: Homo sapiens

7. KINGDOM Animalia
PHYLUM Chordata
CLASS Mammalia
ORDER Carnivora
FAMILY Ursidae
GENUS Ursus
SPECIES Ursus arctos

8. Problems with Traditional Classification
During Linnaeus’s time, scientists classified organisms based on their physical appearance…but today…we know that doesn’t always work.
Ex: Dolphins  Fish or Mammals?
Remember Convergent Evolution  sometimes organisms that are different from each other evolve similar body structures, due to the change in the environment.
This does not mean they need to be classified in the same group…maybe they only evolved similar body structures!
These situations make it very difficult for scientists to classify.

9. Evolutionary Classification
Biologists now group organisms into categories that represent lines of evolutionary descent, not just physical features
Evolutionary classification (phylogeny) is the strategy of grouping organisms together based on their evolutionary history

10. Traditional v/s Evolutionary Classification

11. Classification Using Cladograms
To refine evolutionary classification, biologists now prefer a method called cladistics
Cladistics considers only those characteristics that are new characteristics that arise as lineages evolve over time
Characteristics that appear in recent parts of a lineage but not in its older members are called derived characters
Characteristics that are shared by all members of a lineage are ancestral/primitive characters and should not be used when building cladograms.
Cladogram – a diagram that shows the evolutionary relationships among a group of organisms; includes new characteristics that arise as lineages evolve.

12. Derived Characteristics

13. Anatomy of the Cladogram
Monophyletic group = clade J
Taxon I
F G H
C D E
Paraphyletic group
Lineage (represents a sequence of ancestor-descendent populations)
A B
MONOPHYLETICGROUPS:
include ancestor & all descendents
PARAPHYLETIC GROUPS:
includes ancestor and some, but not all descendent
Node (represents most recent common ancestor of two or more taxa)
Synapomorphy (shared derived character)

14. Monophyletic Clades
A valid clade is monophyletic signifying that it consists of the ancestor species and all its descendants. 14

15. Outgroups Systematists use a method called outgroup comparison
To differentiate between shared derived and shared primitive characteristics
As a basis of comparison we need to designate an outgroup
which is a species or group of species that is closely related to the ingroup, the various species we are studying
Outgroup comparison
Is based on the assumption that homologies present in both the outgroup and ingroup must be primitive characters that predate the divergence of both groups from a common ancestor 15

16. Performing Outgroup Comparison
Who is the outgroup? 16 16

17. Outgroup Comparisons
First, look at the animals we are studying and establish which characteristics that they share & which are unique to each individual species.
Then use these derived characters to build your cladogram.
CELLS
BACKBONE
LEGS
HAIR
OPPOSABLE THUMB
Slug
Catfish
Frog
Tiger
Human

18. Opposable Thumbs
Hair
Legs
Backbone
Cells

19. The Three-Domain System
Molecular analyses have given rise to the most current classification system – the Three Domain System
The 3 Domain System is the most recent classification system and includes:
Bacteria
Archaea
Eukarya

20. Domains are BIGGER/MORE INCLUSIVE than kingdoms
Bacteria
Eubacteria
Archaea
Archaebacteria
Eukarya
Protista
Fungi
Plantae
Animalia
These 2 kingdoms used to be combined into one called “Monera” 20

21. Remember - There are 3 Methods of Classifying Organisms
The 3 Domain System (most current)
Bacteria, Archae, & Eukarya
The 5 Kingdom System (Whittaker)
Monera, Protista, Fungi, Plantae, Animalia
The 6 Kingdom System – still used in conjunction with the 3 domain system
Archaebacteria, Eubacteria, Protista, Fungi, Plantae, Animalia 21

22. Classification of Living Things
Section 18-3
Classification of Living Things
Go to Section:

23. Domain Bacteria Kingdom: Eubacteria Unicellular Prokaryotic
Cell wall of peptidoglycan
Autotrophic or heterotrophic
Examples: Streptococcus, E. Coli

24. Domain Archaea Kingdom: Archaebacteria Unicellular Prokaryotic
Cell walls w/out peptidoglycan
Autotrophic or heterotrophic
Methanogens & halophiles

25. Domain Eukarya

26. Whittaker’s five-kingdom system26

27. Our changing view of biological diversity27

28. The Three Domain System
Describes classification as:
Not all prokaryotes are closely related (not monophyletic)
Prokaryotes split early in the history of living things (not all in one lineage)
Archaea are more closely related to Eukarya than to Bacteria
Eukarya are not directly related to Eubacteria
There was a common ancestor for all extant organisms (monophyletic)
Eukaryotes are more closely related to each other (than prokaryotes are to each other) 28