2. Historical Viewpoints
Humans have always classified things
- Some more formally or rigidly
than others
- Aristotle classified animals based
on blood
- Those with
- Those without
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3. Historical Viewpoints
Humans have always classified things
- Carolus Linnaeus
- Wrote Systema Naturae
- Produced classification system
based on morphology
- Animals groups into species
- Species grouped into genera
- Genera into classes
- Classes into orders
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4. Historical Viewpoints
Humans have always classified things
- Carolus Linnaeus
- Hierarchical classification system
- Ever increasing inclusiveness
- Although Linnaeus got much
wrong, we retain his schema
(with additional classification
units) 4
6. Systematization versus Classification
Classification
- The construction of classes
(groupings of organisms with
common features)
- If a species possesses the feature,
its a member of the group
- If a species lacks the feature, it is
not a member of the group
- Since life is fluid - via evolution -
such a static system is flawed
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8. Binomial Nomenclature
Linnaeus introduced binomial
nomenclature
- Prior, polynomials were used
First name is Genus
Second is species (or specific) epithet
Italicized with genus capitalized
- Homo sapiens
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9. Binomial Nomenclature
Linnaeus introduced binomial
nomenclature
- Prior, polynomials were used
First name is Genus
Second is species (or specific) epithet
Italicized with genus capitalized
- Homo sapiens
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11. Species
What are species?
- A superficially simple question.
- Core concepts
- Common descent
- Smallest distinct grouping
- Reproductive community
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13. Species
Typological Species Concept
- Early concept
- At the time, specie viewed as immutable (unchangeable)
- Type specimen was designated
- Small differences were attributed to variation in individuals
- Large differences were attributed to real differences and new species described
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15. Species
Typological Species Concept
- A few
- What’s a small difference?
- What’s a large difference?
- If species are evolving, aren’t they accruing small differences?
- What about fossil relatives that come before?
- Concept abandoned, but designation of type specimen retained.
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16. Species
Biological Species Concept
- “A species is a reproductive community of populations (reproductively
isolated from others) that occupies a specific niche in nature.”
- Interbreeding is key concept, but often not known if species can
interbreed
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18. Species
Biological Species Concept
- A few.
- When should they be able to interbreed?
- How much reproductive isolation is enough?
- What about asexually reproducing species?
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19. Taxonomic Characters and Phylogenetic
Reconstruction
A goal of systematics is to infer phylogenies (evolutionary trees)
- Accomplished by identifying characters
- Morphological, chromosomal, and molecular
Phylogenetic analyses relies on finding characters that are shared because of
common ancestry
- Such characters are homologies
- When similarity does not reflect common ancestry, such characters are
homoplasies
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20. Taxonomic Characters and Phylogenetic
Reconstruction
Ancestral versus derived character states
- Must determine what was original condition for most recent common
ancestor = ancestral
- All other character states are derived
- Consider teeth in amniotes (birds, reptiles, mammals)
- Contrasting states are presence and absence
- Are the presence of teeth ancestral or derived?
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21. Taxonomic Characters and Phylogenetic
Reconstruction
Ancestral versus derived character
states
- Outgroup comparison
- Use closely related species or
group to make comparison
- If shared by outgroup and
ingroup, character is ancestral
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22. Taxonomic Characters and Phylogenetic
Reconstruction
Ancestral versus derived character states
- Clade - ancestral lineage and all species descended from that lineage
- Derived characters shared within a clade are synapomorphies
- Think feathers for birds
- Ancestral characters shared among species are symplesiomorphies
- Think teeth for amniotes
- Synapomorphies are useful for reconstructing phylogenies, symplesiomorphies
are not.
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23. Taxonomic Characters and Phylogenetic
Reconstruction
Cladogram Versus Phylogenetic Tree
- Although they look similar, phylogenetic trees have additional
information on time since evolution, similarity between taxa, and
interpretations of ancestors
- Cladograms are much simpler
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25. Taxonomic Characters and Phylogenetic
Reconstruction
Monophyly, paraphyly, and polyphyly…
- Monophyly (monophyletic) - contains most recent common ancestor
and all descendants
- Paraphyly (paraphyletic) - contain most recent common ancestor and
some of descendants
- Polyphyly (polyphyletic) - does not contain most recent common
ancestor of all members; often includes two separate evolutionary
origins
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