ORIGIN OF LIFE

Key ConceptsEvidence of Evolution

- comes from biogeography, fossils and comparisons of body form, development and biochemistry among major groups.

Macroevolutionary EventsAsteroid impacts, changing climates and

other global events contributed to the mass extinctions and recoveries, as well as emergence of new species.

Organization of EvidenceNaming and classifying species helps us to

manage data on biodiversity.Cladistics is an evolutionary classification

system that groups species with respect to derived traits that evolved only once, in their last shared ancestor.

Evidence from biogeography• Theory of uniformity prevailed when the

geologists map out vertical stacks of sedimentary rock.

• Recurring geologic events and others had changed the Earth irreversibly.

• `Jigsaw puzzle’ of Africa with the Atlantic coasts of South America?

• Were all continents once part of a bigger one that had splits into fragments and drifted apart?

Evidence from biogeographyFindings as put continential drift into a

broader explanation of Earth’s crustal movements, the plate tectonics theory.

A big connection huge land on collision courses. Masses converged to form supercontinents that split forming new ocean basins Gondwana drifted south from the tropics until crunched into other land masses.

Continental DriftContinents were once joined and have since

“drifted” apartInitially based on shapes Later supported by world distribution of

fossils and existing species, orientation of particles in iron-rich rocks

Plate TectonicsEarth’s crust is fractured into plates

island arc oceanic crust oceanic ridge trench continental crust

subducting plate

athenosphere(plastic layer of mantle)

hot spot

lithosphere(solid layer of mantle)

Fig. 13-6a, p.199

Plate Tectonics• Movement of plates is driven by upwelling of molten rock at mid-oceanic ridges

Evidence from biogeography• The new supercontinent, Pangea extended

from pole to pole. With erosive forces of water and wind resculpted the land.

• Asteroid and meteorites hit the crust which left impacts and long term effect on the global temperature and climate.

• Such changes on land and in the ocean and at atmosphere influenced life’s evolution which took off in a new direction.

Asteroid ImpactsMany past catastrophic

impacts altered the course of evolution

Iridium layer implicates asteroid in extinction of dinosaurs

Asteroids are still a threat

10 mya65 mya260 mya420 mya

where ( seed fern) and Lystrosaurus (a tusked herbivore) evolved

420 mya – early supercontinent Gondwana

260 mya- collisionof land massesForming Pangea

65 mya – Pangea split apart and fragments drifted apart

10 mya – the present position

Life in Pangea 260 myaGlossopteris (Seed fern)Lystrosaurus (a

Therapsidtusked herbivore) evolved

Evidence from FossilsPhysical evidence of organisms that lived in

the distant past.Stratified layers of sedimentary rock are rich

in fossils are historical record of life.The deepest layers generally contain the

oldest fossils.

FossilsRecognizable evidence

of ancient life

What do Fossils Tell Us?Each species is a mosaic of ancestral and

novel traitsAll species that ever evolved are related to

one another by way of descent

StratificationFossils are found in sedimentary rockThis type of rock is formed

in layersIn general, layers closest to the top

were formed most recently

Sedimentary Rock

Record Is IncompleteFossils have been found for about 250,000 speciesMost species weren’t preservedRecord is biased toward the most accessible regionsEven so, the fossil records is substantial enough to

reconstruct patterns and trends in the history of life.

Dating Pieces of the Puzzle• How do we assign fossils to a place of time?• How do we know how old they really are?• By using the radiometric dating, this is

possible.• Understand the nature of radioisotope decay.• A radioisotope is an atom of an element with

an unstable nucleus which decays spontaneously until the atom becomes a more stable element.

Radiometric Dating• The proportions of the radioisotope to its

daughter elements in a sample can be used to calculate the sample’s age.

• This applies when the rate of decay for each isotope is constant.

• A predictable number of a radioisotope’s atoms in any sample will decay in a characteristic time span.

• No change in pressure, temperature or chemical state alters that rate.

Radiometric Dating• Can be used to reveal the age of rocks.• E.g. with uranium 238-to-lead ratio in the

oldest rocks, geologists predicted that the Earth formed more than 4.6 billion years ago.

• Dating the sedimentary rock yield s the date its component materials formed but not the date they actually sedimented.

• The only way to date the old fossils is to find their position relative to the rocks.

Radiometric datingFossils that retain some

carbon can be dated directly by measuring their ratio of 12C to 14C.

Trace amounts of 14C were incorporated in the tissues of a living mollusk.

As long the mollusk was living, the proportion of 14C to 12C remained the same in the tissue.

Radiometric datingWhen mollusk died, it

stopped gaining carbon.

Over time, the proportion of 14C to 12C in its remain fell due to the radioactive decay of the 14C.

Half of the 14C had decayed in 5,370 years.

Radiometric datingWhen such fossil is found

and measured of its 14C to 12C ratio to determine the half-life reductions since death.

The ratio turns out to be one eighth of the 14C to 12C ratio in living organisms.

Thus, the mollusk lived about 16,000 years ago.

Radiometric DatingOrganism becomes buried in ash or

sedimentsOrganic remains become infused

with metal and mineral ionsCarbon 14 dating

Radiometric Dating

after two half-lives

after one half-life

parent isotope innewly formed rock

The decay if radioisotopes at a fixed rate to more stable forms.

The half –life of each kind of radioisotope is the time it takes for 50% of a sample to decay.

After two half-lives, 75% of the sample has decayed , and so on.

Geologic Time Scale

Boundaries based on transitions in fossil record

Cambrian period

Proterozoic eon2,500

myaArchean eon and earlier

Ordovician period

Silurian periodDevonian period

544

505

440

410

Carboniferous period

Permian period

Cretaceous period

Tertiary periodQuaternary period

360

286

248

213

145

65

Cambrian period

Jurassic periodTriassic period

Paleozoic era

Mesozoic era

Cenozoic eraPhanerozoic eon

MacroevolutionMajor patterns and trends among lineagesRates of change in geologic time

5:28:41 A.M.,origin of eukaryotes

2:05:13 A.M.origin of prokaryotes

11:59:59 A.M., first humans

11:44:30 A.M., dinosaurs, flowering plants

Earth’s crust solidifies

Fig. 13-5, p.198

11:21:10 A.M., origin of mammals

10:51:7 A.M., early fishes

Macroevolution

Evidence from Comparative MorphologyEvolution mans heritable changes in lines of

descent.Comparisons of body form and structures of

major groups of organisms yield clues for the evolutionary relationships.

Comparative morphology is study of body forms and structures of major groups of organisms.

Comparative MorphologyEvidence of a common ancestor maybe due

to the similarities in the internal structure of one or more body parts.

Similar body parts which reflect shared ancestry are homologous structures.

used differently in different groups, but same genes direct their development.

Morphological DivergencePopulation of a species diverge genetically

after gene flow ends between them.Over time, some of the traits that define the

species also diverge.Change from body form of a common

ancestor is a macroevolutionary pattern.

Morphological Divergence

Change from body form of a common ancestor

Produces homologous structures

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1

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1

1

1

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early reptile

pterosaur

chicken

bat

porpoise

penguin

human

Morphological ConvergenceSimilar body parts are not always homologous

and may have evolved independently in separate lineages as adaptations to the same environmental pressures.

Such parts are named as analogous structures which look alike in different lineages but did not evolve in a shared ancestor.

Evolved independently after lineages diverged.

Evolution of similar body parts in different lineages is called morphological convergence.

Morphological Convergence

body wall (exoskeleton)

strong membrane (extension of wall)

wing veins

Fig. 13-9c2, p.202

Morphological Convergence

Limbs with 5 digits

wings

birdscrocodilesHumansbatsInsects

wings

wings

The evolutionary tree diagram shows that wings evolvedindependently in three separate lineages that bled to bats,birds and insects.

Key conceptsWith morphological divergence, a body

inherited from a common ancestor becomes modified differently in different lines of ancestor. Such parts are homologous structures.

With mophological convergence, body parts appear alike evolved independently in different lineages, not in a common ancestor. Such parts are analogous structures.

Changes in patterns in developmentComparing the patterns of embryonic

development often yields evidence of evolutionary relationships

Similarities in patterns of development are often clues to shared ancestry.

Mutation in master genes are capable of launching body plans in new evolutionary directions. Changes in these and other genes that affect development may result in structural differences among related lineages.

Genes and variationHomoetic genes guide formation of specific

body parts during embryonic development.A mutation in one homoetic hgene can

disrupt the body’s form.Consequences, may be severe or maybe

advantageous.e.g. formation of flowers.

Genes and VariationHow many legs?Impact of mutations on animal evolution.Embryos of many vertebrate species develop

in similar ways.Heritable changes in the onset, rate or

completion of early steps in development occur.

How many legs? Mutations in master

genes may explain why animals differ in the number of appendages.

Dlx, a homoetic gene makes limbs from wherever is expressed.

Fossil animal unrestricted expression of Dlx gene in Cambrian times.

Variations in control over Dlx expression, showed by green fluorescence in embryonic appendages of

velvet walking worm

Blue dye in mouse embryo’s foot

Chimps and HumansGene duplications may account for some

major functional differences among species that have nearly identical genes.

Last shared ancestor of chimpanzees and humans lived between 6-4 mya.

Not more than 98% of human DNA is identical with chimp DNA.

What accounts for the morphological and behavioral differences between the two ?

Skull bones : bones of face and brain chamber in humans increase in size at same rate from infant to adult while facial bones in chimps grow faster than the brain chamber humans and chimps have different faces.

Proportional Changes in Skull

chimpanzee

human

Molecular EvidenceBiochemical traits shared by species

show how closely they are relatedCan compare DNA, RNA, or proteins

Clues in DNA, RNA and ProteinsAll species have a mixture of ancestral and

novel traits, including biochemical ones.The kind and number of traits that species

share are clues to evolutionary relationships.Biochemical similarity is greatest among the

most closely related species and smallest among the most remote.

Comparing ProteinsCompare amino acid sequence of proteins

produced by the same gene Human cytochrome c (a protein)

Identical amino acids in chimpanzee proteinChicken protein differs by 18 amino acidsYeast protein differs by 56

raccoon

red panda

giant panda

spectacled bear

sloth bear

sun bear

Asiaticblack bear

American black bear

brown bear

polar bear

An example of how biochemical comparisons can assist in constructing and refining the evolutionary trees.Red pandas, giant pandas and brown bears was constructed using sequence Comparisons of mitochondrial and nuclear DNA. Findings indicated that red pandamaybe more closely related to skunks, weasels and otter rather than to raccoons.

Sequence ConservationCytochrome c functions in electron

transport in cells.Deficits in this vital protein would be lethalLong sequences are identical in wheat,

yeast, and a primate indicating the a.a. sequences has been highly conserved even in these three evolutionary distant lineages.

yeastwheatprimate

Yeast (top row)Wheat (middle)Primate (bottom)

Amino acids are identical

Nucleic Acid ComparisonUse single-stranded DNA or RNAHybrid molecules are created,

then heatedThe more heat required to break hybrid,

the more closely related the species

Molecular ClockAssumption: “Ticks” (neutral

mutations) accumulation in the DNA at a constant rate .

Count the number of differences in the DNA base sequences or a.a. sequences to estimate time of divergence among species or groups of them.

grown in watergrown on land

Differences in form between two plants of the same speciesSaggitaria sagittifolia. The leaf shapes are responses to different conditions in the environment, not the differences in the genes

Reproductive Isolation

Cornerstone of the biological species conceptSpeciation is the attainment of reproductive

isolationReproductive isolation arises as a by-product

of genetic change

Biological Species Concept “Species are groups of interbreeding natural

populations that are reproductively isolated from other such groups.”Ernst Mayr , evolutionary biologist

In other words,Species as one or more groups of individuals that potentially can interbreed, produce fertile offspring and do not interbreed with other groups.

Reproductive IsolationIn nature, sexually reproducing species

attain and maintain separate identities by reproductive isolation ---the end of gene exchanges between populations.

New species arise by the evolutionary process of speciation.

This begins as gene flow ends between populations which diverge genetically as mutation, genetic drift and natural selection operate in each one independently.

Genetic DivergenceGradual accumulation of differences in the

gene pools of populationsNatural selection, genetic drift, and mutation

can contribute to divergenceGene flow counters divergence

Genetic Divergence

time A time B time C time D

daughter species

parent species

Reproductive isolating mechanismsSpeciation occur after a very long period of

divergence, or after one generation.As two populations diverge, reproductive

isolation mechanisms arise.Such mechanisms are heritable aspects of

body form, function or behavior that prevent interbreeding between different species and they reinforce differences between diverging populations.

Reproductive Isolating Mechanisms

Prevent pollination or mating

Block fertilization or embryonic

development

Cause offspring to be weak or sterile

Reproductive IsolationMechanisms

Prezygotic Isolation MechanismMechanical isolation

Temporal isolation

Behavioral isolation

Ecological isolation

Gamete incompatibility /mortality

Mechanical IsolationWasp and zebra orchid.The plant release some

chemicals that attract the insect which mistook the flower as the female.

Temporal isolation among cicadas

Reproductive Isolation

Temporal Isolation

CicadaTiming of

reproduction differs between 3 species.

If interbreeding occurs, it will take them to get together once every 221 years.

Behavioral IsolationBehavioral differences stop gene flow

between related species.Males and females engage in courtship

displays before sex.Female albatross recognizes the singing,

wing spreading or head bobbing of a male of her species as an overture to sex.

Female of different species ignore this behavior.

Behavioral IsolationAlbatrosses

Ecological SpeciationOccurs to two populations in different

microenvironments .Manzanita species at foothills of Sierra

Nevada: one at 600-1850m and the other at 750-3350m. They hybridize rarely. Both conserve water but one is adapted to less intense water stress while the other species lives in drier hillsides.

Thus, cross pollination is unlikely to happen.

Gamete IncompatibilityIf and whenever different species interbreed

anyway, reproductive isolating mechanism does happen.

Reproductive cells of different species have molecular incompatibilities, so fertilization does not occur.

If whenever zygote form,but…Postzygotic isolating mechanisms take place.Two consequences happen:(1)Hybrid inviability : Hybrid embryos die early

or the new individuals die before they can reproduce

(2)Hybrid sterility : Hybrid individuals cannot make functional gametes

Thus, no offspring, sterile offspring, weak offspring die before reproducing.

Postzygotic Isolating Mechanisms

Early death

Sterility or sterile F2

offspring

Low survival rates

Llama-Camel Hybrid

Models for Speciation

Allopatric speciation

Sympatric speciation

Parapatric speciation

Allopatric SpeciationSpeciation in geographically isolated

populations Some sort of barrier arises and prevents

gene flowEffectiveness of barrier varies with speciesGene flow ends, and genetic divergence

give rise to daughter species.

Allopatric Speciationilamas

camels

vicunas

Connection of land bridge between twocontinents

Extensive Divergence Prevents Inbreeding

Species separated by geographic barriers will diverge genetically

If divergence is great enough it will prevent inbreeding even if the barrier later disappears

ArchipelagosIsland chains some distance from continents

Galapagos IslandsHawaiian Islands

Colonization of islands followed by genetic divergence sets the stage for speciation

1

23

4

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23

4

1

2

A few individuals of a species on the mainland reach isolated island 1. Speciation follows genetic divergence in a new habitat.

Later in time, a few individuals of the new species colonize nearby island 2. In this new habitat, speciation follows genetic divergence.

Speciation may also follow colonization of islands 3 and 4. And it may follow invasion of island 1 by genetically different descendents of the ancestral species.

3

4

Hawaiian IslandsVolcanic origins,

variety of habitats Adaptive radiations:

Honeycreepers: in absence of other bird species, they radiated to fillnumerous niches Housefinch (Carpodacus)

Ancestral type

Akepa (Loxops coccineus)Fig. 13-18d1, p.209

Speciation in Hawaiian Honeycreepers

Hawaiian honeycreepers

An example of a burst of speciations on an isolated archipelago.

These species are adapted to diverse food sources, such as insects, seeds, fruits and floral nectar.

Speciation without a BarrierSympatric speciation

Species forms within the home range of the parent species

Parapatric speciationNeighboring populations become distinct

species while maintaining contact along a common border

Sympatric SpeciationDaughter species arise from a population even

in the absence of a physical barrier.Polyploidy – speciation occur in an instant with

a change in the chromosome number where- duplication of somatic cells do not divide during mitosis or- nondisjunction in meiosis resulting gametes with unreduced chromosome number

Speciation by PolyploidyChange in chromosome number

(3n, 4n, etc.)Offspring with altered chromosome number

cannot breed with parent populationCommon mechanism of speciation in

flowering plants

Figure 18.9Page 299

Possible Evolution of WheatTriticum monococcum (einkorn)

T. aestivum (one of the common bread wheats)

Unknown species of wild wheat

T. turgidum(wild emmer)

T. tauschii (a wild relative)

42AABBDD14AA 14BB 14AB 28AABB 14DDXX

cross-fertilization, followed by a spontaneous chromosome doubling

Sympatric speciation in wheat

Possible Evolution of Wheat

Sympatric Speciation in African Cichlids

Studied fish species in two lakesSpecies in each lake are most likely

descended from single ancestorNo barriers within either lake

Sympatric Speciation in African CichlidsFeeding preferences localize species in

different parts of lake

Parapatric SpeciationOccurs when one population extends across a

broad region encompassing diverse habitats.Different habitats exert distinct selection

pressures on parts of population and maybe divergences leading towards speciation.

Hybrids form in between are less fit than individuals on either side of it.

Population maintaining contact along common border evolve into distinct species.

Parapatric SpeciationPopulations in contact along a common

border

giant velvet worm

blind velvet worm

We’re All RelatedAll species are related by descent

Share genetic connections that extend back in time to the prototypical cell

Gradual ModelSpecies emerge through many small

changes accumulating over time Fits well with evidence from certain

lineages in fossil recordFossilized shells from vertical

sequence of sedimentary rock layers.First shell (bottom) – 64.5 mil yrs oldMost recent (top) – 68 mil yrs oldThis analysis confirms the

evolutionary order matches their geological sequence.

Punctuation ModelSpeciation model in which most changes in

morphology are compressed into brief period near onset of divergence

Supported by fossil evidence in some lineages

Adaptive RadiationBurst of divergence Single lineage gives rise to many

new speciesNew species fill vacant adaptive

zone Adaptive zone is “way of life”Cenozoic radiation of mammals

Adaptive Radiations of Mammals

CoevolutionProcess that close ecological interactions

among species that cause them to evolve jointly.

Each species adapts to changes in the other; over time the two may become interdependent.

Some coevolved species no longer survive without one another.

Predator-prey ; host-parasite; flower-pollinator

ExtinctionIrrevocable loss of a speciesMass extinctions play a major

role in evolutionary historyFossil record shows 20 or more

large-scale extinctionsReduced diversity is followed by

adaptive radiation

Who Survives?Species survival is somewhat randomAsteroids have repeatedly struck Earth,

destroying many lineagesChanges in global temperature favor lineages

that are widely distributed

Evolutionary TheoryInvolves processes of both macroevolution

and microevolution.All come to explain the same thing--- the tree

of life that connects all species by ancestry.

MicroevolutionInvolves processes:- Natural selection preserves or erodes species

cohesion depending on environmental pressures- Mutation original source of alleles- Gene flow preserves species of cohesion- Gene drifterodes species of cohesionStability or change in a species is the outcome of

balances / imbalances among all of the above processes. The effects are influenced by population size and the prevailing environmental conditions.

MacroevolutionDescribe genetic changes within a species or

population.Is our name for large-scale pattern such as one

species giving rise to several others, the origin of major groups, and major extinction events.

Involves:- Genetic persistence basis of unity of life

(biochemical and molecular basis of inheritance)- Genetic divergence basis of life’s diversity (adaptive

radiation, branching with rates and times of change)- Genetic disconnect extinction (end of line of the

species brought by catastrophic events)

Organizing information about speciesConnections among species, from ancient to

recent, are evidence of evolution.Species are put into groups based on what we

know about their evolutionary relationships.Taxonomy is a set of rules of naming organisms

and classifying them into series of ranks based on their traits.

e.g. every organism has a unique two-part scientific name. Genus-species. (Homo sapien)

TaxonomyThe identification, naming, and

classification of speciesSomewhat subjectiveInformation about species can be

interpreted differently

The higher taxaA taxon (plural, taxa) is an organism or group

of them.Categories above species are higher taxa.Each higher taxon consists of a group of the next lower taxon.

Lead to the classification system developed by a Swedish naturalist, Carolus Linnaeus (1707-1778), who separated animals and plants according to certain physical similarities and gave identifying names to each species.

Linnaeus’s system classified plants and animals on seven levels, using Latin and Greek words.

Principles and importance of taxonomy

Taxonomy as of science of classificationImportant to find, identify, study, describe

and understand the distribution of organisms grouping/classify organisms according to

their shared common features (as of taxon)based on seven levels of taxon:

Taxa (plural) Taxon (singular)KingdomPhylumClass OrderFamilyGenusSpecies

Levels of taxonKingdom largest group sharing common features

Phylum Subdividision of kingdom; contain large number of organism that have one / two fundamental features

Class Group of orders within a phylum

Order Group of related families

Family Group of related genera

Genus Group of similar and closely-related species

Species Group of individuals which share a large number of features and capable of inbreeding to produce fertile offspring

Take note!!Number of organisms

in each taxon decreases as we goes down the levels of taxon.

Number of shared characteristics increases as we go up the levels of taxon.

Kingdom

Phylum

Class

Order

Family

Genus

Species

Classification of a single species of animal

How a brown squirrel is classified: Kingdom (Animalia, or “animal”) Phylum (Chordata, or “has a backbone”) Class (Mammalia, or “has a backbone and nurses its young”)Order (Rodentia, or “has a backbone, nurses its young, and

has long, sharp front teeth)Family (Scuridae, or “has a backbone, nurses its young, has

long, sharp front teeth, and has a bushy tail) Genus (Tamiasciurus, or “has a backbone, nurses its young,

has long, sharp front teeth, has a bushy tail, and climbs trees) Species (hudsonicus, or “has a backbone, nurses its young,

has long, sharp front teeth, has a bushy tail, climbs trees and has brown fur on its back and white fur on its underparts)

It is not necessary to go through the entire seven-level classification system to identify a plant or animal.

Two names are sufficient—the genus and species names. Thus, the scientific name for the brown squirrel is

Tamiasciurus hudsonicus.

Because two names are used, the system used by Linnaeus and based on Latin is known as the binomial (two names) system of nomenclature (naming).

The naming of species and other taxa follows a set of rules:

(1) International Code of Botanical Nomenclature (ICBN) for plants,

(2) International Code of Zoological Nomenclature (ICZN) for animals.

The name game

Naming SpeciesEach species has a two-part nameFirst part is generic nameSecond part is species nameUrsus arctos = brown bear

Ursus americanus = black bearBufo americanus = American toad

Rules of the gameConsistency in using the system of classification.The generic (genus) name is the first and always

given with capital letterThe specific (species) name comes second and

always starts with small letter.Both names should either be written in Italics or

underlinedScientific name should be written in full the first

time it is used. But after that, it can be abbreviated.

If the species is unknown, then the abbreviation `sp.’ can be used.

Some general rules for nomenclature: All taxa must belong to a higher taxonomic group.

Often a newly discovered organism is the sole species in a single genus, within a single family...etc.

The first name to be validly and effectively published has priority. This rule has caused numerous name changes, especially with fossil organisms: Brontosaurus is invalid, and the correct name for the big sauropod dinosaur is Apatosaurus, Eohippus (the tiny "dawn horse") is invalid and should be referred to as Hyracotherium. Sometime, however, names can be conserved if a group of systematists agrees.

All taxa must have an author. When you see a scientific name such as Homo sapiens L, the L stands for Linnaeus, who first described and named that organism. Most scientists must have their names spelled out.

Taxonomy of a selected plant species.

Note that the Kingdoms have a great deal more types of creatures in them than do species.

The system is successful because :each particular organism has its own unique scientific name

can see that two species are closely related based on similar/same genus.

Examples of Classification

Kingdom

GenusSpecies

FamilyOrderClassPhylum

Plantae

JuniperusJ. occidentalis

CupressaceaeCuoniferalesConiferopsida Coniferophyta

Plantae

VanillaV. planifolia

OrchidaceaeAsparagalesMonocotyledonaeAnthophyta

Animalia

MuscaM. domestica

MuscidaeDipteraInsectaAnthropoda

Animalia

HomoH. sapiens

HominidaePrimatesMammaliaChordata

western juniper vanilla orchid housefly human

Taxonomic Classification

Taxonomic Classification

PhylogenyThe scientific study of evolutionary

relationships among speciesPractical applications

Allows predictions about the needs or weaknesses of one species on the basis of its known relationship to another

Six-Kingdom ClassificationBacteria Archaea Protists Plants Fungi Animals

Three-Domain SystemBacteria Archaea Eukarya

Tree of Life

Classification systems

Evolutionary tree for plants

CladisticsCladistics is a set of methods by which we

can determine the evolutionary relationships and used in phylogenetics classification schemes.

Organisms are grouped by shared derived traits.

Monophyletic group - A group of species all descended from an ancestral species in which a particular derived trait first evolved.

Patterns of Change in a LineageCladogenesis

Branching patternLineage splits, isolated populations diverge

AnagenesisNo branchingChanges occur within single lineageGene flow throughout process among its

populationIn time, species becomes so different from

its ancestor becomes a new species and the ancestral species extinct.

Evolutionary Trees

ancestral stock

species 1

species 2 species 3

Summarize information about relationships among groups

branch point (time of genetic divergence,speciation under way)

suspected branching

Evolutionary tree diagram

Evolutionary Trees

Cladistic approachA clade is a group of species that share a

set of derived traits (those that do not appear in the most recent ancestor).

A clade may correspond to the Linnaean group but not every Linnaean group correspond to a clade.

With biochemistry approach and DNA sequencing methods, data used to define a clade can be updated frequently .

A Cladogram

Evolutionary Tree

Summarize our best understanding of the pattern of evolution for a group of organisms.

Evolutionary Tree

Current Evolutionary Tree

How to construct a CladogramUsing a selection of traits among groups to

construct a simple cladogram, step by step approach.

Is an estimate of ‘who came from whom’Has no time bar with absolute dates.Reflect morphological and biochemical comparisonsHelp to visualize monophyletic groups as sets within

sets.Reference:

http://www.eeescience.utoledo.edu/Faculty/Dwyer/Biodiversity/ConstructingCladograms.htm

Step 1Start with a list of taxa that are to be fit into

the cladogram (the ingroup) and their derived characters. 

Choose an outgroup; a taxa that shares a primitive character with the ingroup, but exhibits none of the derived characters. 

Step 2Fill in a character table that will be used to

make the cladogram.  The taxon with the least number of derived characters should be the first row.  The taxon with the greatest number of derived characters should be the last row. 

The character that is seen in the greatest number of taxa should be the first column.  The character that is exhibited in the least number of taxa should be the last column. 

Use ones and zeroes to represent presence (1) or absence (0) of specific characters in specific species.

Make a Venn diagram to place the 8 animals in groups to illustrate those characteristics which different animals have in common.

chimphumanchimpanzee

Amphioxus : no back bone

Lamprey : has backboneSunfish : has jaws

Lizard : has amniotic egg

Bear: has mammary glands Newt : has four limbs

Step 3Build the cladogram step-by-step.  Start with

the first character (first column).  The outgroup is the only taxon that doesn't

exhibit the first character.  Separate it from the other taxa on the

cladogram.  Remember that the outgroup shares a

common ancestor with the ingroup.  Each split in the cladogram marks a separate

evolutionary event.   

Step 4By looking at the completed cladogram, we

can see which species are most closely or distantly related. 

In this example, humans are more closely related to chimpanzees, than to any other taxon on the cladogram. 

Do the Bring Home Quiz provided in the next slide. You are to complete the assignment as during the next lecture, answers shall be given and marking shall be carried out at the same time.

Marked assignment must be hand over back to the instructor as marks shall be counted as part of the assessment.

Those did not bring in their assignment for the next lecture are considered FAIL (zero % is given).

BRING HOME QUIZ (20 marks)Follow the instruction provided in the text

below.For the following animals, construct your own

cladogram (+ means that the animal has the given derived character trait) showing :

character table (3 marks) ;Venn diagram (7 marks) and completed cladogram (8 marks).  *Make sure that you apply the steps as

outlined from the lecture.

BRING HOME QUIZDerived Characters

segmented jaws hair placenta multicellular limbs

kangaroo + + + - + +earthworm + - - - + -amoeba - - - - - -lizard + + - - + +cat + + + + + +sponge - - - - + -salmon + + - - + -

Based on the completed cladogram that you have constructed, answer the following questions:

Which ingroup is most closely related to sponges?(1 mark)________________________________

Which ingroup is most distantly related to sponges?(1 mark) ________________________________

TOTAL : 20 marks