Tree of Life
Chapter 26
Where Are We Going?
 Taxonomy
 Scientific discipline of classifying and naming organisms
 Phylogeny
 Interpreting diagrams of evolutionary history
 Application
 What evolutionary history says about biological diversity
Binomial Nomenclature
 Common names for casual usage, but not accurate
 What animals come to mind you when hear the word ‘fish’?
 Different words depending on language
 Biologist use Latin scientific names
 Carolus Linnaeus
 2 part system: genus and specific epithet
 Homo sapiens or Panthera pardus
Hierarchical (Linnaean) Classification
 Linnaeus grouped named
animals into categories
 genus Panthera: leopard (P.
pardus), lion (P. leo), tiger
(P.tigris), & jaguar (P. onca)
 Based on morphological
similarities
 Used by taxonomists
 Taxon is any level of the
hierarchy
 Review: How can you
remember the hierarchical order
of taxons?
 Doesn’t always reflect
evolutionary history
Phylogenetic Trees
 Diagrams hypotheses of
evolutionary history of
organisms
 Degree of relatedness to
ancestors
 Used by systematists
 Can reclassify if mistake found
 Only implies pattern of
descent, not time or age
 Branch means common
ancestor, not taxon from taxon
Reading Phylogenetic Trees
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Series of branch points
Root is last common
ancestor of tree
Sister taxa share an
immediate ancestor
Which of the trees
below depicts a
different evolutionary
history from the other
two?
Homology vs Analogy
 Homologies are similarities due to shared ancestry
 Used to construct phylogenies
 Analogies are similarity due to convergent evolution
 What is convergent evolution?
 ‘Moles’: marsupial vs eutherian; similar lives
 Wings: bats vs. insects vs. birds; relation to cats
 More points of resemblance make more likely ancestor was
shared
 Applies to morphological and molecular
similarities
Constructing Phylogenetic Trees
 Must first separate homologous from analogous
 Systematists then infer phylogeny using cladistics
 Using common ancestry to classify organisms
 Create clades or groups containing an ancestral species and all
descendants
Clades vs. Taxons
 Similar to taxons because both are nested groups
 Equivalent only if it is monophyletic, containing ancestor
and ALL descendants
 Paraphyletic contains ancestor and SOME descendants
 Polyphyletic contain taxa with different ancestors
Shared … Characteristics
 Ancestral originates in an ancestor of the taxon
 Backbones are an example for mammals, why?
 Derived is a novelty unique to a clade
 Hair is an example for mammals, why?
 Ancestral can qualify as derived at deeper branches
 What branch point allows backbones to be shared derived
characteristics?
Constructing Phylogenies
Use the 1st appearance of
each shared derived
characteristic
Determine the
outgroup and
ingroup
Determined from
morphology,
paleontology, embryonic
development, or genes
Compare members of
the ingroup to each other
and to the outgroup
The Genome’s Role in Phylogeny
 Nucleic acids and other molecules are also used to determine
and test hypotheses about evolutionary relationships
 Important for organisms that are unlikely to have
morphological similarities or organisms without fossil records
 Fungi, plants, and animals
 Prokaryotes and other microorganisms
 Determine relationships at all levels of the Tree of Life
 Rates of gene evolution varies
 rRNA is slow = good for relationships that diverged 100’s of
millions of years ago
 mtDNA is rapid = good for recent evolution
Evolving Genomes
 Orthologous genes
 Homologous genes in different
species through speciation
 Can diverge only after
speciation
 E.g cytochrome C (ETC
protein)
 Paralogous genes
 From gene duplication =
multiple copies in the same
genome
 Can diverge within a species
 E.g 1000’s of olfactory
receptors
 Humans and mice 99%
orthologous; and yeast 50%
The Changing Tree of Life
 Initially 2 Kingdoms
 Plants: bacteria (cell wall), chloroplast organims, fungi (sessile)
 Animals: protozoans (movement and eat)
 5 Kingdoms
 Monera: prokaryotes
 Protista: unicellular organisms
 Plantae, Fungi, and Animalia: eukaryotes
 Recently 3 Domains
 Molecular evidence that prokaryotes as different from each other as
eukaryotes
 Bacteria: most prokaryotes, close to chloroplasts and mitochondria
 Archaea: diverse prokaryotes living in extreme environments
 Eukarya: cells with true nuclei
Domain Systems
1 example of Life’s
connections
Most of living
organisms are
single-celled
Red lines are
multicellular
Monera gone
because it contains 2
domains
Protista
disappearing due to
diversity and
similarity to other
eukarya
Alternate Form of Life Connection
Horizontal gene
transfer: exchange
of info between
genomes
Mitochondrial
ancestor of bacteria
and eukarya
Chloroplasts of
bacteria and green
plants
Can explain
inconsistency of
trees
Only diagrammable
as a ring