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Phylogeny & the Tree of LifeChapter 26
Phylogeny & SystematicsPhylogeny:
◦ Evolutionary history of a species or group of species◦ Determined by evidences from fossil record, homologous
structures, molecular homologies Systematics:
◦ Helps us understand phylogeny (data analysis of phylogeny)
26.1Phylogenies show evolutionary relationships
TaxonomyGrouping according to
evolutionary similaritiesBinomial nomenclature
(Linnaeus)Domains SpeciesTaxon (plural: taxa):
named taxonomic hierarchy◦Ex: Panthera is the taxon
at the genus level
Phylogenetic TreeLinks
taxonomy and phylogeny
Branch points◦Divergence of
two lineages from a common ancestor
Most recent common ancestor
How to read a phylogenetic tree
26.2
Phylogenies are inferred from morphological and molecular data
Recall:Homology
◦Similarities due to common ancestryAnalogy
◦Similarities due to convergent evolution
Morphology & DNAPhysical traits and genetics are
homologous in organisms with recent shared common ancestors
Molecular SystematicsUses DNA and other molecules to
hypothesize evolutionary history
26.3
Shared characters are used to construct phylogenetic trees
CladisticsScience of constructing a
cladogram
CladisticsClades
◦Groups of organisms sharing a common ancestor
MonophyleticA valid clade is
monophyletic, it consists of the ancestor species and all its descendants
Paraphyletic
A paraphyletic clade consists of an ancestral species and some, but not all, of the descendants
PolyphyleticA
polyphyletic clade includes many species that lack a common ancestor
Species Change Over Time (Nodes)
Characteristics Shared primitive
character ◦ Homologous structure
that is older than the branching of a particular clade from other members of that clade
◦ It is shared by more than just the taxon we are trying to define.
◦ Example – mammals all have a backbone, but so do other vertebrates.
Characteristics
Shared derived character ◦ New evolutionary
feature, unique to a particular group
◦ Example - all mammals have hair, and no other animals have hair.
Ingroup & OutgroupIn: Group of study (make
comparisons)Out: Group that diverged prior to
ingroup
26.6
New information continues to revise our understanding of the tree of life
A Changing Approach to Classification of LifeNew evidence means continued
revision of classification◦Genome (DNA) sequencing
Tree of LifeCurrent
classification:◦Three domains
6 kingdoms
3 Domains
First life on Earth
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