BIO120H1 Lecture Notes - Lecture 10: Carl Linnaeus, Willi Hennig, Binomial Nomenclature

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12 Jul 2017
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BIO120: Phylogenetics and Macroevolution (Lecture 10)
Macroevolution
-big picture, genealogy of life
-experiments less common
Darwin’s First Evolutionary Tree
-in July 1837, Darwin began his notebook on “The Transmutation of Species”
-aside from discovering mechanism of natural selection, also very interested in genealogy
-thinking about descent with modification
-Darwin did the first phylogenetic tree
-the one he put in The Origin: the only figure in The Origin
Carolus Linnaeus (1707-1778)
-the “father” of taxonomy
-binomial nomenclature
genus and species: struggled to explain complexity of life, came up with classification
-hierarchical system of classification:
kingdoms
phyla
classes
orders
families
genera
species
What is the Purpose of Biological Classification?
-name is a key to the literature on an organism
without a name, hard to find stuff out about an organism
-has predictive power
-enables interpretation of origins and evolutionary history
Taxon
-a taxonomic unity at any level (plural = taxa), neutral term
-e.g. kingdoms
phyla
classes
orders
families
genera
species
Taxonomy vs. Systematics
-taxonomy: the theory and practice of classification
-systematics: the study of biodiversity and the evolutionary relationships among
organisms
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Schools of Taxonomy
-philosophical wars of the 70s and 80s
-phenetics (original): classifying species based solely on overall resemblance
now largely dead
in the 70s, all taxonomists were pheneticists, looked at morphology
-cladistics (new): classifying species on the basis of their phylogenetic relationships
started in Germany, slowly replaced phenetics
many sources of data (morphology, chromosome number, sequence data)
Willi Hennig (1913-1976)
-the birth of cladistics and the building of phylogenetic trees
-phylogenetic trees provide a depiction of the evolutionary relationships among groups of
organisms important to appreciate, they are a hypothesis about evolutionary history
A Phylogenetic Tree
-branching descent
-ingroup: extant, group of individuals interested in studying
-outgroup: close relatives we can put into relationships
-nodes: speciation events
-internodes: ancestors of species
Monophyletic vs. Non-Monophyletic Groups
-monophyletic group: a single ancestor gave rise to all species in that taxon and no
species in any other taxon
Hennig brought in this idea
taxa have to be monophyletic in order for us to classify them in trees
-non-monophyletic group: a taxon whose members are derived from two or more
ancestral forms not common to all members
Grouping Species into Higher Taxa
-taxon 1 is monophyletic and constitutes a clade (all taxa derived from an immediate
common ancestor); all taxa descended from species A
-taxon 2 is non-monophyletic (not what we want to achieve in taxonomy)
-monophyletic classifications are preferred
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