Phylogeny and Systematics How do we classify organisms

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Phylogeny and SystematicsHow do we classify
organisms?
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Review

• So far we have looked at
• 1. The history of ideas surrounding how
  organisms change.
• 2. Darwins ideas of change and how natural
  selection works
• 3. Genetic basis of natural selection
• 4. How new species can arise

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Now ask the question

• How do we organize our knowledge about species
  and put that into some meaningful classification?
• Determine the phylogeny - the evolutionary
  history of a species or group of species.

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First step Naming organisms
Binomial nomenclature Invented by Carl Linnaeus
Every species has two names Genus
species e.g. Homo sapiens
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• An aside
• A couple of rules about using species names
• 1. They are always underlined or in italics
• 2. The name of the genus is always capitalized
  but the species name never is.
• 3. Its a name like yours - you dont refer to a
  species as the Homo sapiens - just Homo
  sapiens.
• 4. The plural of species is species and the
  plural of genus is genera (NOT genuses)

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Hierarchical Classification
Species name for a leopard
Genus for all leopards and their relatives
Family for all cats
Order for all carnivorous mammals
Class for all fur-bearing animals
Phylum for animals with spinal columns
Kingdom for all organisms without photosynthesis
Domain for all organisms with eukaryotic cells
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This information can also be presented as a
phylogenetic tree
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How are trees constructed?

• Based on different kinds of homologous structures
  called characters
• Shared primitive characters those structures
  that are shared with larger related groups -
  e.g. all vertebrates share a backbone
• Shared derived characters those structures that
  are shared by a smaller group (or clade) - e.g
  all mammals share milk production

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A simple classification of vehicles

• Imagine that you have sampled a number of objects
  and found
• the following characteristics
• 2 wheels, no engine
• 4 wheels, gas engine, glassed box on back
• 4 wheels, gas engine, no box on back
• 4 wheels, diesel engine, enclosed box on back
• 1 wheel, no engine

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A simple classification of vehicles

• 2 wheels, no engine
• 4 wheels, gas engine, glassed box on back
• 4 wheels, gas engine, no box on back
• 4 wheels, diesel engine, enclosed box on back
• 1 wheel, no engine

What are the shared primitive and derived
characters?
Wheels - primitive (all have them)
wheels
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A simple classification of vehicles

• 2 wheels, no engine
• 4 wheels, gas engine, glassed box on back
• 4 wheels, gas engine, no box on back
• 4 wheels, diesel engine, enclosed box on back
• 1 wheel, no engine

What are the shared primitive and derived
characters?
Wheels - primitive (all have them)
Engine - possessed by 3 of 5
No engine
Engine
wheels
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A simple classification of vehicles

• 2 wheels, no engine
• 4 wheels, gas engine, glassed box on back
• 4 wheels, gas engine, no box on back
• 4 wheels, diesel engine, enclosed box on back
• 1 wheel, no engine

What are the shared primitive and derived
characters?
2 wheels
1 wheel
Wheels - primitive (all have them)
Engine - possessed by 3 of 5
Wheels - objects with no engine have either 1 or
two wheels
No engine
Engine
wheels
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A simple classification of vehicles

• 2 wheels, no engine
• 4 wheels, gas engine, glassed box on back
• 4 wheels, gas engine, no box on back
• 4 wheels, diesel engine, enclosed box on back
• 1 wheel, no engine

No box
Box
What are the shared primitive and derived
characters?
2 wheels
1 wheel
Wheels - primitive (all have them)
Engine - possessed by 3 of 5
Wheels - objects with no engine have either 1 or
two wheels
No engine
Engine
Box - objects have a box on the back or not
wheels
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A simple classification of vehicles
Glass
Enclosed

• 2 wheels, no engine
• 4 wheels, gas engine, glassed box on back
• 4 wheels, gas engine, no box on back
• 4 wheels, diesel engine, enclosed box on back
• 1 wheel, no engine

No box
Box
What are the shared primitive and derived
characters?
2 wheels
1 wheel
Wheels - primitive (all have them)
Engine - possessed by 3 of 5
Wheels - objects with no engine have either 1 or
two wheels
No engine
Engine
Box - objects have a box on the back or not
wheels
Box - glassed in or enclosed
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SUV
Van
A simple classification of vehicles
Glass
Enclosed

• 2 wheels, no engine
• 4 wheels, gas engine, glassed box on back
• 4 wheels, gas engine, no box on back
• 4 wheels, diesel engine, enclosed box on back
• 1 wheel, no engine

Car
No box
Box
Unicycle
Bicycle
What are the shared primitive and derived
characters?
2 wheels
1 wheel
Wheels - primitive (all have them)
Engine - possessed by 3 of 5
Wheels - objects with no engine have either 1 or
two wheels
No engine
Engine
Box - objects have a box on the back or not
wheels
Box - glassed in or enclosed
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SUV
Van
Shared primitive and derived characters?
Glass
Enclosed
These change depending on the level of
classification you are talking about e.g.
Wheels are a shared primitive character of all
vehicles but the engine is a shared primitive
character for the truck, car and SUV.
Car
No box
Box
Unicycle
Bicycle
2 wheels
1 wheel
No engine
Engine
wheels
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How are trees constructed?
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History of Life on Earth
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Hypothesized stages in the appearance of life

• Abiotic synthesis of organic molecules
• Polymerization of small molecules into larger
  ones
• Formation of polymers into protobionts
• Origin of a self-replicating molecule (protobiont)

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Kinds of evidence used Fossil Record
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Dating Fossils
If fossils are used to establish the history of
life, there must be a way of telling how old they
are.
Radiometric dating -use radioisotopes - not
stable and will change (or decay) into other
kinds of isotopes
e.g. carbon-14 (C14)
Nitrogen-14 (N14)
Parent isotope
Daughter isotope
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Dating Fossils
Sequence of events
Stops accumulating carbon (C14)
Original level (C14)
Ancient creature dies
C14 begins to decay and is replaced by N14
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Dating Fossils
Sequence of events
Stops accumulating carbon (C14)
Original level (C14)
Ancient creature dies
C14 begins to decay and is replaced by N14
Ratio of C14 N14 ( ) time
since the animal died (and radioisotope decay
began)
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Molecular Clocks

• timing evolutionary events by looking at rates of
  change of sequences in genes
• these sequences change at constant rates

Number of sequence changes
Time since groups diverged
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History of Life
What does the fossil record and dating fossils
tell us about the history of life on Earth?
Oldest rocks
Oldest eukaryotes
All other plants and animals
Origin of earth
Oldest cell fossils
Algae and first invertebrates
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History of Life
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History of Life
Key events

• Origin of prokaryotes
• Orgin of eukaryotes
• Origin of multicellular
• eukaryotes

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1. Origin of Prokaryotes
Prokaryote - a type of organism lacking a
membrane-enclosed nucleus and membrane-enclosed
organelles.
bacteria
Oldest known fossils - stromatolites - bacterial
mats
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2. Origin of Eukaryotes
Eukaryote - a type of organism with a
membrane-enclosed nucleus and membrane-enclosed
organelles.
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2. Origin of Eukaryotes
Endosymbiosis
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2. Origin of Eukaryotes
Endosymbiosis
Animals and Fungi
Plants
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3. Origin of Multicellular Eukaryotes
First multicellular organisms Colonial
-show cellular differentiation
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Tree of Life (very simplified!)
Bacteria
Universal ancestor
Archaea
Protista
Plants
Eukarya
Amoebas
Fungi
Animals