Chapter 26:Phylogeny and the Tree of Life
Essential Knowledge1.b.2 – Phylogenetic trees and
cladograms are graphical representations (models) of evolutionary history that can be tested (26.1-26.3).
1.d.2 – Scientific evidence from many different disciplines supports models of the origin of life (26.6).
PhylogenyPhylon = tribe, geny = genesis or origin
The evolutionary history of a species or a group of related species
Found in fossils and the fossil record
FossilsAny preserved remnant or
impression of a past organism.
Types:◦ 1. Mineralized◦ 2. Organic matter◦ 3. Trace◦ 4. Amber
Mineralized FossilsFound in sedimentary rock.
Minerals replace cell contents.
Ex: bone, teeth, shellsOrganic Matter Fossils
• Retain the original organic matter
• Ex: plant leaves trapped in shale
• Comment – can sometimes extract DNA from these fossils
Trace FossilsFootprints and other
impressions No organic matter present
Amber• Fossil tree resin• Preserve whole specimen• Usually small insects, etc
Fossils - LimitationsRare eventHard to find FragmentaryDating
Fossil Dating Methods
1. Relative - by a fossil's position in the strata relative to index fossils
2. Absolute - approximate age on a scale of absolute time
2. 2 types: 1. Radioactive
Estimated from half-life products Ex: Carbon 14, Potassium 40
2. Isomer Ratios
What do fossils tell us?
That the geographical distribution of organisms has changed over time
Reason? – The land formations of the earth have changed through continental drift
Continental DriftThe movement of the earth's
crustal plates over timeDrift is correlated with
events of mass extinctions and adaptive radiations of life
Pangaea250 million years agoOne super continentMany life forms brought into
contact with each otherResult:
◦ Geographic isolation◦ New environments formed, others lost◦ As environments changed, so did life!
Mass ExtinctionsThe sudden loss of many
species in geologic timeMay be caused by asteroid hits
or other disastersResult:
◦ Area open for surviving species to exploit
◦ Rapid period of speciation (adaptive radiation)
◦ Many new species are formed in short amount of time
SystematicsThe study of biological
diversity.Uses evidence from the fossil
record and other sources to reconstruct phylogeny.
Goal: ◦ To have Taxonomy reflect the
evolutionary affinities or phylogeny of the organisms.
Areas of Systematics
1. Phylogeny- tracing of evolutionary relationships
2. Taxonomy- the identification and classification of species
TaxonomyNatural to humans.Modern system developed by
Linnaeus in the 18th century.Includes:
1.Binomial nomenclature: naming system Ex: Homo sapiens
2.Hierarchical system: arranges life into groups Ex: Kingdom species
Levels
Kingdom Phylum Class Order Family Genus Species
Question?How do we relate Taxonomy
to evolution?◦ Not all “likeness” is inherited from a
common ancestor.◦ Problem is of homology vs. analogy
Homology and Analogy
Homology – likeness attributed to shared ancestry (divergent and parallel evolution)◦Ex: forelimbs of vertebrates
Analogy – likeness due to convergent evolution (not necessarily a shared ancestral lineage)◦Ex: wings of insects and birds
Convergent EvolutionWhen unrelated species have
similar adaptations to a common environment
Ex: Sharks and dolphins fins; wings of bats, butterflies and birds
Taxonomy and Evolution
We need methods to group organisms by anatomical similarities and phylogenies
One possible method is Molecular Systematics◦ Compares similarities at the molecular
level Ex: DNA, Proteins
DNA ComparisonsA direct measure of common
inheritanceThe more DNA in common,
the more closely relatedMethods:
◦ Restriction Mapping◦ DNA Sequencing
Protein ComparisonsExamines the Amino Acid
sequence of homologous proteins.
Ex: Cytochrome C Study
Molecular ClockCompares molecular
differences to fossil recordsResult is a way to estimate
divergence in species where the fossil record is missing
Chapter 25: The
History of Life on Earth
Essential Knowledge1.a.4 – Biological evolution is supported
by scientific evidence from many disciplines, including mathematics (25.2).
1.b.1 – Organisms share many conserved core processes and features the evolved and are widely distributed among organisms today (25.1, 25.3).
1.c.1 – Speciation and extinction have occurred throughout the Earth’s history (25.4).
Essential Knowledge, Continued1.d.1 – There are several
hypotheses about the natural origin of life on Earth, each with supporting scientific evidence (25.1 & 25.3).
4.b.4 – Distribution of local and global ecosystems changes over time (25.4).
Fossil Record
Earliest - 3.5 billion years oldEarth - 4.5 billion years oldPoint - Life on earth started
relatively soon after the earth was formed
Chemical Evolution
Def – the evolution of life by abiogenesis
Steps:1. Monomer Formation2. Polymer Formation3. Protobiont Formation4. Origin of Heredity
Primitive Earth Conditions
Reducing atmosphere present
Simple molecules◦Ex: H2O, CH4, H2, NH3
Complex molecule formation:◦ Requires an energy source
UV Radioactivity Heat Lightning/Electricity
Oparin and Haldane, 1920s
Hypothesized steps of chemical evolution from primitive earth conditions
Miller and Urey, 1953Tested Oparin and Haldane’s
hypothesisExperiment - to duplicate
primitive earth conditions in the lab
Results: Organic monomers formed (include amino acids)
Other Investigator's Results
All 20 Amino Acids foundOthers
◦Sugars◦Lipids◦Nucleotides◦ATP
HypothesisEarly earth conditions could
have formed monomers for life's origins
These early monomers eventually joined together to form large, complex polymers
Genetic Information
DNA RNA ProteinToo complex for early lifeWere there other forms of
genetic information?
RNA HypothesisRNA as early genetic
informationRationale
◦RNA polymerizes easily◦RNA can replicate itself◦RNA can catalyze reactions including protein synthesis
RibozymesRNA catalysts found in
modern cellsCould be a possible relic from
early evolutionary processes
DNA hypothesis
Developed later as the genetic information
Why? ◦More stable than RNA
ClassificationKingdom: Highest Taxonomic
categoryOld system: 2 Kingdoms
1. Plant2. Animal
5 Kingdom SystemR.H. Whittaker - 1969System most widely used
todayUse three main
characteristics to categorize:◦ 1. Cell type◦ 2. Structure◦ 3. Nutrition mode
MoneransEx: Bacteria, CyanobacteriaProkaryotic
Ex: Amoeba, parameciumEukaryotic cellsUnicellular or colonialHeterotrophs
Protists
FungiEx: Mushrooms, MoldsEukaryoticUnicellular or MulticellularHeterotrophic - external
digestionCell wall of chitin
PlantaeEx: Flowers, TreesEukaryoticMulticellularAutotrophicCell wall of Cellulose/Silicon
AnimaliaEx: Animals, HumansEukaryoticMulticellularHetrotrophic - internal
digestionNo cell wall
Other SystemsMultiple Kingdoms – split life into
as many as 8 kingdomsDomains – a system of
classification that is higher than kingdom◦ Based on molecular structure for
evolutionary relationships◦ Gaining wider acceptance
3 Domains1. Bacteria – prokaryotic2. Archaea – prokaryotic, but
biochemically similar to eukaryotic cells
3. Eucarya – the traditional eukaryotic cells
SummaryIdentify the steps of Chemical
EvolutionRecognize the conditions on early
Earth.Recognize the limitations of the
fossil record.Recognize some of the key
events in the history of Earth.
