Chapter 20
Classification of
Living Things
Classification of
Living Things
2
Outline
Taxonomy
Binomial System
Species Identification
Classification Categories
Phylogenetic Trees
Systematics
- Taxonomy (naming of organisms)
- Classification (placing species in the proper categories)
Systematics Today
Cladistic Systematics
Phenetic Systematics
Classification Systems
The Five Kingdom System
The Three Domain Ssytem
Classification of
Living Things
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Taxonomy
Branch of biology concerned with identifying,
naming, and classifying organisms
Began with the ancient Greeks and Romans
Aristotle classified organisms into groups
such as horses, birds, and oaks
John Ray (1627–1705)
Believed that each organism should have a
set name
Otherwise, “men…cannot see and record
accurately.”
Classifying Organisms
4
Taxonomy:
Binomial System
Classification of
Living Things
Mid-eighteenth century, Linnaeus developed
the binomial system of nomenclature
First word is genus name
Second word is specific epithet
- Refers to one species (of potentially many)
within its genus
A species is referred to by the full binomial
name (Genus species)
Genus name can be used alone to refer to a
group of related species
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Carolus Linnaeus
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Taxonomy:
Distinguishing Species
Classification of
Living Things
Distinguishing species on the basis of
structure can be difficult
Members of the same species can vary in
structure
Attempts to demonstrate reproductive
isolation is problematic because:
- Some species hybridize, and
- Reproductive isolation is difficult to observe
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Members of a Species
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Hybridization between species
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Classification of
Living Things
Classification Categories
Modern taxonomists use the following
classification:
Species
Genus – one or more species
Family – one or more genera
Order – one or more families
Class – one or more orders
Phylum – one or more classes
Kingdom – one or more phyla
Domain – one or more kingdoms
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Hierarchy of Taxa for
Parthenocissus quinquefolia
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Classification of
Living Things
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Classification Categories
The higher the category, the more inclusive
Organisms in the same domain have general
characteristics in common
In most cases, classification categories can
be subdivided into additional categories
Superorder
Order
Suborder
Infraorder
Classification of
Living Things
13
Phylogenetic Trees
Systematics - the diversity of organisms at all
levels
One goal of systematics is to determine
phylogeny (evolutionary history) of a group
Phylogeny often represented as a
phylogenetic tree
A diagram indicating lines of descent
Each branching point:
- Is a divergence from a common ancestor
- Represents an organism that gives rise to two
new groups
Classification and Phylogeny
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Classification of
Living Things
Phylogenetic Trees
Classification lists the unique characters of
each taxon and is intended to reflect
phylogeny
Primitive characters:
- Present in all members of a group, and
- Present in the common ancestor
Derived characters:
- Present in some members of a group, but
- Absent in the common ancestor
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Classification of
Living Things
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Tracing Phylogeny
Fossil Record
Fossil record is incomplete
It is often difficult to determine the phylogeny
of a fossil
Homology
Refers to features that stem from a common
ancestor
Homologous structures are related to each
other through common descent
Analogy
Similarity due to convergence
Ancestral Angiosperm
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Classification of
Living Things
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Tracing Phylogeny
Convergent Evolution
The acquisition of a feature in distantly related
lines of descent
The feature is not present in a common
ancestor
Parallel Evolution
The acquisition of a feature in two or more
related lineages
The feature is not present in a common
ancestor
Convergent Evolution
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Classification of
Living Things
Molecular Data
Protein Comparisons
Immunological techniques
- Degree of cross reaction used to judge relationship
Amino acid sequencing
- Similar sequence in same protein indicates close
relationship
RNA and DNA Comparisons
Systematics assumes:
- Two species with similar base-pair sequences are
assumed to be closely related
- Two species with differing base-pair sequences are
assumed to be only distantly related
Molecular Clocks
Use non adaptive nucleotide sequences
Assumed constant rate of mutation over time
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Ancestry of Giant Pandas
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Molecular Data
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Classification of
Living Things
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Cladistic Systematics
Traces evolutionary history of the group
under study
Uses shared derived characters to:
Classify organisms, and
Arrange taxa into a cladogram
- A cladogram is a special type of phylogenetic
tree
- A clade is an evolutionary branch that includes:
A
common ancestor, together with
 All
its descendent species
Constructing a Cladogram
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Classification of
Living Things
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Parsimony
Cladists are always guided by the principle of
parsimony
The arrangement requiring the fewest
assumptions is preferred
This would:
- Leave the fewest number of shared derived
characters unexplained
- Minimize the number of assumed evolutionary
changes
The reliability of a cladogram is dependent on
the knowledge and skill of the investigator
Alternate, Simplified Cladograms
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Cladistic Versus Traditional View of
Reptilian Phylogeny
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Classification of
Living Things
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Phenetic Systematics
Assumes it will never be possible to construct
a truly phylogenetic classification system
Species are classified according to the total
number of shared similarities
Disregards assumed phylogenetic
considerations
Ignores issues of convergent or parallel
evolution
Classification of
Living Things
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Traditional Systematics
Mainly uses anatomical data
Classify organisms using assumed phylogeny
with emphasis on phenotype
Stress both common ancestry and degree of
structural difference among divergent groups
Construct phylogenetic trees by applying
evolutionary principles to categories
Not strict in making sure all taxa are
monophyletic
Classification of
Living Things
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Classification Systems
Until the middle of the twentieth century,
biologists recognized only two kingdoms
Plantae (plants)
Animalia (animals)
Protista (protists) were added as third
kingdom in the 1880s
Whittaker expanded to five kingdoms in 1969
by adding Fungi and Monera
Classification of
Living Things
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Three-Domain System
The Bacteria and Archaea are so different
they have been assigned to separate
domains
Similar in that both are asexually reproducing
unicellular prokaryotes
Distinguishable by:
Difference in rRNA base sequences
Plasma membrane chemistry
Cell wall chemistry
Classification of
Living Things
Three-Domain System
Domain Eukarya
Unicellular and multicellular organisms
Cells with a membrane-bounded nucleus
Sexual reproduction common
Contains four kingdoms
- Kingdom Protista
- Kingdom Fungi
- Kingdom Plantae
- Kingdom Animalia
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The Three-Domain
System of Classification
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The Three Domains of Life
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Classification of
Living Things
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Review
Taxonomy
Binomial System
Species Identification
Classification Categories
Phylogenetic Trees
Systematics
- Taxonomy (naming of organisms)
- Classification (placing species in the proper categories)
Systematics Today
Cladistic Systematics
Phenetic Systematics
Classification Systems
The Five Kingdom System
The Three Domain System
Ending Slide Chapter 20
Classification of
Living Things