Lecture 4: Reading And Building Phylogenies

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Systematics

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the study of evolutionary relationships between organisms

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Taxonomy

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the classification and naming of organisms

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character

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any quality or quantity that can be compared between the taxa under study.

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character state

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characters are usually described in terms of their states, for example: "hair present" vs. "hair absent," where "hair" is the character, and "present" and "absent" are its states

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polarity of characters

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ancestral vs. derived

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taxon (pl. taxa)

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Any named group of organisms, not necessarily a clade

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Ingroup

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In a cladistic analysis, the set of taxa which are hypothesized to be more closely related to each other than any are to the outgroup.

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Outgroup

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In a cladistic analysis, any taxon used to help resolve the polarity of characters, and which is hypothesized to be less closely related to each of the taxa under consideration than any are to each other.

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Monophyletic group

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includes only those taxa derived from a single common ancestor

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Paraphyletic group

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includes only some of the descendants of a common ancestor, but not all of them

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Polyphyletic group

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includes taxa derived from more than one common ancestor

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Three Schools of Thought in Evolutionary Biology

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1) Phenetics or Numerical taxonomy

2) Cladistics or Phylogenetic systematics

3) Evolutionary Systematics

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Phenetics or Numerical taxonomy Classifications are based on ________.

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Measurable, morphological characters, not evolutionary relationships

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Four Tenets of Cladistics

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1. Cladogenesis (speciation) is the only quantifiable feature of evolution

2. All taxa must be monophyletic

3. All evolutionary relationships must be measured in terms of recency of descent from a common ancestor

4. The rank of a taxon is automatically determined by the age of the common ancestor

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Maximum Parsimony

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under this criterion, the shortest possible tree that explains the data is considered best‐ the optimal tree will minimize the amount of homoplasy (i.e., convergent evolution, parallel evolution, and evolutionary reversals)