Title: The Tree of Life
1The Tree of Life
2Why 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.
3Linnaeuss 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
4Binomial 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
5Linnaeuss System of Classification
- Linnaeuss 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
6Human Classification
- Kingdom Anamalia
- Phylum Chordata
- Subphylum Vertebrata
- Class Mammalia
- Order Primates
- Family Hominidae
- Genus Homo
- Species Homo sapiens
7KINGDOM Animalia
PHYLUM Chordata
CLASS Mammalia
ORDER Carnivora
FAMILY Ursidae
GENUS Ursus
SPECIES Ursus arctos
8Problems with Traditional Classification
- During Linnaeuss time, scientists classified
organisms based on their physical appearancebut
todaywe know that doesnt 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 groupmaybe they only evolved similar
body structures! - These situations make it very difficult for
scientists to classify.
9Evolutionary 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
10Traditional v/s Evolutionary Classification
11Classification 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.
12Derived Characteristics
13Anatomy 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)
14Monophyletic Clades
- A valid clade is monophyletic signifying that it
consists of the ancestor species and all its
descendants.
15Outgroups
- 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
16Performing Outgroup Comparison
17Outgroup 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
18Opposable Thumbs
Hair
Legs
Backbone
Cells
19The 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
20Domains are BIGGER/MORE INCLUSIVE than kingdoms
Domains Kingdoms
Bacteria Eubacteria
Archaea Archaebacteria
Eukarya Protista Fungi Plantae Animalia
These 2 kingdoms used to be combined into one
called Monera
21Remember - 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
22Section 18-3
Classification of Living Things
Go to Section
23Domain Bacteria
- Kingdom Eubacteria
- Unicellular
- Prokaryotic
- Cell wall of peptidoglycan
- Autotrophic or heterotrophic
- Examples Streptococcus, E. Coli
24Domain Archaea
- Kingdom Archaebacteria
- Unicellular
- Prokaryotic
- Cell walls w/out peptidoglycan
- Autotrophic or heterotrophic
- Methanogens halophiles
25Domain Eukarya
26Whittakers five-kingdom system
27Our changing view of biological diversity
28The 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)