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Brief Introduction to the Theory of Evolution and Phylogenetic Reconstruction
Anders Gorm Pedersen Molecular Evolution Group Center for Biological Sequence Analysis
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Classification: Linnaeus
Carl Linnaeus
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Classification: Linnaeus
Hierarchical system Kingdom (Rige) Phylum (Række) Class (Klasse) Order (Orden) Family (Familie) Genus (Slægt) Species (Art)
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Classification depicted as a tree
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Classification depicted as a tree
Species Genus Family Order Class
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Theory of evolution Charles Darwin
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Phylogenetic basis of systematics
Linnaeus: Ordering principle is God. Darwin: Ordering principle is shared descent from common ancestors. Today, systematics is explicitly based on phylogeny.
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Darwin’s four postulates
More young are produced each generation than can survive to reproduce. Individuals in a population vary in their characteristics. Some differences among individuals are based on genetic differences. Individuals with favorable characteristics have higher rates of survival and reproduction. Evolution by means of natural selection Presence of ”design-like” features in organisms: quite often features are there “for a reason”
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Theory of evolution as the basis of biological understanding
”Nothing in biology makes sense, except in the light of evolution. Without that light it becomes a pile of sundry facts - some of them interesting or curious but making no meaningful picture as a whole” T. Dobzhansky
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Trees: terminology
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Trees: terminology
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Trees: representations
Three different representations of the same tree
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Trees: rooted vs. unrooted
A rooted tree has a single node (the root) that represents a point in time that is earlier than any other node in the tree. A rooted tree has directionality (nodes can be ordered in terms of “earlier” or “later”). In the rooted tree, distance between two nodes is represented along the time-axis only (the second axis just helps spread out the leafs) Early Late
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Trees: rooted vs. unrooted
A rooted tree has a single node (the root) that represents a point in time that is earlier than any other node in the tree. A rooted tree has directionality (nodes can be ordered in terms of “earlier” or “later”). In the rooted tree, distance between two nodes is represented along the time-axis only (the second axis just helps spread out the leafs) Early Late
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Trees: rooted vs. unrooted
A rooted tree has a single node (the root) that represents a point in time that is earlier than any other node in the tree. A rooted tree has directionality (nodes can be ordered in terms of “earlier” or “later”). In the rooted tree, distance between two nodes is represented along the time-axis only (the second axis just helps spread out the leafs) Early Late
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Trees: rooted vs. unrooted
In unrooted trees there is no directionality: we do not know if a node is earlier or later than another node Distance along branches directly represents node distance
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Trees: rooted vs. unrooted
In unrooted trees there is no directionality: we do not know if a node is earlier or later than another node Distance along branches directly represents node distance
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Reconstructing a tree using non-contemporaneous data
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Reconstructing a tree using present-day data
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Data: molecular phylogeny
DNA sequences genomic DNA mitochondrial DNA chloroplast DNA Protein sequences Restriction site polymorphisms DNA/DNA hybridization Immunological cross-reaction
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Morphology vs. molecular data
African white-backed vulture (old world vulture) Andean condor (new world vulture) New and old world vultures seem to be closely related based on morphology. Molecular data indicates that old world vultures are related to birds of prey (falcons, hawks, etc.) while new world vultures are more closely related to storks Similar features presumably the result of convergent evolution
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Molecular data: single-celled organisms
Molecular data useful for analyzing single-celled organisms (which have only few prominent morphological features).
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