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.