Evolution Lectures 2005 Evolution Lectures 2005

Modified 2008Modified 2008

M.ElizabethM.Elizabeth

Evolutionary EvidenceEvolutionary Evidence

• Comparative anatomyComparative anatomy - living things are - living things are constructed along the same linesconstructed along the same lines

• TaxonomyTaxonomy - life is hierarchical (“tree of - life is hierarchical (“tree of life”)life”)

• Geology Geology - Earth is ancient, fossils record - Earth is ancient, fossils record evolution, small changes can have big evolution, small changes can have big effectseffects

• BiogeographyBiogeography - same environment yields - same environment yields different organismsdifferent organisms

Definition: EvolutionDefinition: Evolution• 'Evolution' is a description of AND an

explanation of the history of species - their origins, how they change, survive, become extinct.

•So evolution concerns BOTH a historical account of life on earth AND an attempt to explain how observed changes have happened.

•Defined as the slow change of organisms over time and a change in the frequency of certain alleles in the population.

Overview of LectureOverview of LectureEvidence that evolution has occurred•Comparative anatomy•Taxonomy•Geology and fossils•Biogeography

How does evolution occur?•Malthus and natural selection•How does “perfection” arise?•How does novelty arise?

A changing world view A changing world view (200-300 years ago)(200-300 years ago)

Earth is young

In the 17th century Archbishop James Ussher used the Bible to date the origin of the earth as 4004 B.C. (Vice-chancellor of Cambridge refined this to the morning of Sunday, October 23rd, 4004 B.C.)

Fixity of species

Species are permanent, natural kinds. They do not change.A fixed plan of creation.

Design

Living things seem designed for a purpose, and a design implies a designer

A changing world viewA changing world viewEarth is ancient

Approximately 4,500,000,000 years old (radioactive isotopes)

Species evolve

Living things are constantly changing, new species arise and others go extinctThe history of life is contingent

Adaptation

Fit between organisms and their environment is due to natural selection (“blind watchmaker”)Organisms are often imperfectly created

Darwin’s place in scienceDarwin’s place in science

UnityUnity

How we are the same and yet How we are the same and yet differentdifferent

All living organisms contain All living organisms contain four macromoleculesfour macromolecules

– carbohydratescarbohydrates– lipidslipids– proteinsproteins– nucleic acidsnucleic acids

Life is constructed Life is constructed on a similar planon a similar plan

Human and chimpanzee chromosomes

Human and chimpanzee facial expressions

Life is constructed on a similar Life is constructed on a similar plan – homologous structures.plan – homologous structures.

Vestigial organsVestigial organs

The eye bulbs of blind, cave-dwelling creatures, such as the grotto salamander (Typhlotriton spelaeus).

The anthers and pollen of asexual dandelions.

Vestigial organs in Vestigial organs in humanshumans

Appendix

Nictating membrane in eye

What is Embryology?What is Embryology?

• Embryology is the study Embryology is the study development of the embryo.development of the embryo.

• An embryo is the young animal An embryo is the young animal undergoing development within the undergoing development within the egg or womb. egg or womb.

• Embryology is used to illustrate Embryology is used to illustrate common ancestry because there are common ancestry because there are similarities between organisms' similarities between organisms' embryological development.embryological development.

Hind limbs in whalesHind limbs in whales

Whale embryo

Modern whale Fossil whale

Human embryo at 5 weeksHuman embryo at 5 weeks

Similarities Similarities during during embryonic embryonic developmentdevelopment

7 properties of life7 properties of life

1.Ordered structure2.Reproduction3.Growth and development4.Energy utilization5.Response to environment6.Homeostasis7.Evolutionary adaptation

• How do we recognise evolution?

• What causes evolution?• Does evolution lead to perfection?

What is evolution?

Decent with modification

What is evolution?

We can redefine evolution as a change over time

Trait value

Time t Time t+x

Low High

• How do we recognise evolution?

• What causes evolution?

• Does evolution lead to perfection?

Causes of Evolution

There are 5 causes ‘The accidental toolkit’:

• Natural selection• Genetic drift• Mutation• Gene flow• Nonrandom mating

Causes of Evolution

1. Natural Selection

There are 3 important points:

• Variation

• Differential success

Causes of Evolution

1. Natural Selection

There are 3 important points:

• Variation

• Differential success

• Inheritance

Over time there will be mainly white individuals

Causes of Evolution

1. Natural Selection

Fitness

Differences in reproductive success

- relative contribution to the next generation • survival • access to mates • breeding success

Causes of Evolution

1. Natural SelectionExample: the peppered moth

Coloration is a camouflage:

Causes of Evolution

1. Natural SelectionExample of the industrial melanism of the peppered moth

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Causes of Evolution

2. Genetic DriftRandom changes in the frequency of traits to chance factors

Occurs under 2 conditions: founder effect bottleneck effect

Causes of Evolution

2. Genetic Drift

Founder effect - when a new population is a small sample of a large population

King George III

Example: Porphyria

1 / 80,000

1 / 8,000

Causes of Evolution

2. Genetic Drift

Bottleneck effect - when only a small fraction of the population survives that is no longer representative

Example: Lions living in the Ngorogoro

1960 1975 1990

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Causes of Evolution

2. Genetic Drift

Bottleneck effect - when only a small fraction of the population survives that is no longer representative

Example: Lions living in the Ngorogoro

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Causes of Evolution

3. Mutation

Changes in an organism’s DNA

Hopeful monsters

Probably of little importance

Causes of Evolution

4. Gene Flow

Changes due to movement from one place to another

20% RED

+ 2 REDS 27% RED

Causes of Evolution

5. Nonrandom Mating

Individuals with particular traits are more likely to mateSexual Selection

Boys fight Boys look fetching

Causes of Evolution

5. Nonrandom Mating

Boys fight - inter-sexual competition

The winner will mate

Causes of Evolution

5. Nonrandom Mating

Boys look fetching - intra-sexual competition

The male with the best ornament will be chosen

• How do we recognise evolution?

• What causes evolution?

• Does evolution lead to perfection?

Does Evolution lead to Perfection

Does the ability to perform improve? - ADAPTATION

Just-so-stories

The elephant’s child

Does Evolution lead to Perfection

How do we know there is an ADAPTATION?

Adaptation happens only by selection, all other changes are like a lottery

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Does Evolution lead to Perfection

The course of evolution depends on:

• Historical constraints

• Existing variation

• Compromise

• ‘Accidental toolkit’

The Tale of the Monkey

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The Tale of the Monkey

Natural Selection Edits Variation

Variation is the fuel of evolution- next

Evolution is not the work of a designer, but the work of a tinkerer.

Natural Selection:

If variation of a trait within a population has a genetic

basis,and some variants have

greater survival and reproduction,

then, over time, the favored trait will predominate in the population.

Requirements:

More individuals areborn each generationthan can survive: the "Struggle for Existence"

Variation in a trait within a population. (Giraffe's necks)

Giraffes with longer necks get better food, have more babies(have an advantage in the struggle for existence)

Longer necks beget longer necks(variation is heritable)

Results:

Over time, average neck length increases

Under other conditions, over longer periods of time, new species form(e.g. the Okapi)

Evolution as a result of chance events

(e.g. Dinosaurs!)

Role of chance in evolution: Extinctions

Catastrophic EventCatastrophic Event• Cretaceous-TertiaryCretaceous-Tertiary (K (KT) transition:T) transition:

– Dinosaurs disappear “instantaneously” 65 Dinosaurs disappear “instantaneously” 65 myr agomyr ago

• Meteorite eventMeteorite event– Luis and Walter Alvarez: transition rich in Luis and Walter Alvarez: transition rich in

iridiumiridium (Ir), like in meteorites (Ir), like in meteorites– High KHigh KT Ir the same around the worldT Ir the same around the world– High abundances of osmium, gold and High abundances of osmium, gold and

platinumplatinum– Shocked quartz: formed at high temperature Shocked quartz: formed at high temperature

and pressureand pressure– Spherical rock droplets: molten rock Spherical rock droplets: molten rock

solidifies in airsolidifies in air– Soot (some sites): widespread firesSoot (some sites): widespread fires– 200 km crater in Yucat200 km crater in Yucatáán peninsula: 10 km n peninsula: 10 km

meteoritemeteorite

Mass Extinctions Mass Extinctions MethodsMethods

– ~10~1088 hydrogen bombs hydrogen bombs– Tidal wave up most of low-lying Tidal wave up most of low-lying

North AmericaNorth America– Forest fires worldwide Forest fires worldwide harsh harsh

winter winter plants die plants die lack of food lack of food– Acid rain Acid rain kill life in the oceans too kill life in the oceans too– 99% of all living died, 75% of all 99% of all living died, 75% of all

species became extinctspecies became extinct

Colonization of LandColonization of Land

• MicrobesMicrobes– Hard to know when colonization occurredHard to know when colonization occurred– Easy to find water and UV protection on Easy to find water and UV protection on

landland• Larger organismsLarger organisms

– Remained in the oceans longer, particularly Remained in the oceans longer, particularly animalsanimals

– Need to draw water from the soil but Need to draw water from the soil but energy from sunlightenergy from sunlight

– Plant colonization of land began ~ 475 myr Plant colonization of land began ~ 475 myr agoago

• OzoneOzone– Main UV protection, but history Main UV protection, but history

even more uncertain than that of even more uncertain than that of oxygenoxygen

• AlgaeAlgae– DNA: plants evolved from algaeDNA: plants evolved from algae– Algae Algae plants in small pools during plants in small pools during

periods of dryness?periods of dryness?• Carboniferous periodCarboniferous period

– Animals followed plants to land Animals followed plants to land within 75 myrwithin 75 myr

– Large forests ~ 360 myr ago Large forests ~ 360 myr ago coal coal

Other Mass ExtinctionsOther Mass Extinctions

• Multiple mass extinctionsMultiple mass extinctions– At least 5 big onesAt least 5 big ones– Many smaller onesMany smaller ones– Event like KEvent like KT every ~100 myrT every ~100 myr– Old seafloor craters would be gone by nowOld seafloor craters would be gone by now– Nearby supernova explosions also every ~ 100 myrNearby supernova explosions also every ~ 100 myr– Magnetic reversals every few myr remove cosmic-Magnetic reversals every few myr remove cosmic-

ray protection of the magnetosphereray protection of the magnetosphere

• EvolutionEvolution– Catastrophes create opportunities, not just disasterCatastrophes create opportunities, not just disaster– May have more effect than gradual evolutionMay have more effect than gradual evolution

Continuing Impact ThreatContinuing Impact Threat

• Impact objectsImpact objects– MeteorMeteor: small (<1 cm), ~ 25 million per day, burn : small (<1 cm), ~ 25 million per day, burn

in atmospherein atmosphere– FireballFireball (not UFO): medium (10 cm (not UFO): medium (10 cm 1 m), explode 1 m), explode

in the atmospherein the atmosphere– MeteoriteMeteorite: large (> few m), vaporizes solid rock, : large (> few m), vaporizes solid rock,

leaving a craterleaving a crater– Tunguska meteorite (1908): <30 m, energy of Tunguska meteorite (1908): <30 m, energy of

several atomic bombs, sound heard round the several atomic bombs, sound heard round the globe, no crater (comet?)globe, no crater (comet?)

• FutureFuture– Probability declines rapidly with sizeProbability declines rapidly with size– Currently able to detect threat, but not divert itCurrently able to detect threat, but not divert it

Colonization of LandColonization of Land

• MicrobesMicrobes– Hard to know when colonization occurredHard to know when colonization occurred– Easy to find water and UV protection on landEasy to find water and UV protection on land

• Larger organismsLarger organisms– Remained in the oceans longer, particularly animalsRemained in the oceans longer, particularly animals– Need to draw water from the soil but energy from sunlightNeed to draw water from the soil but energy from sunlight– Plant colonization of land began ~ 475 myr agoPlant colonization of land began ~ 475 myr ago

• OzoneOzone– Main UV protection, but history even more uncertain than that of Main UV protection, but history even more uncertain than that of

oxygenoxygen• AlgaeAlgae

– DNA: plants evolved from algaeDNA: plants evolved from algae– Algae Algae plants in small pools during periods of dryness? plants in small pools during periods of dryness?

• Carboniferous periodCarboniferous period– Animals followed plants to land within 75 myrAnimals followed plants to land within 75 myr– Large forests ~ 360 myr ago Large forests ~ 360 myr ago coal coal

KKT EventT Event

• Cretaceous-TertiaryCretaceous-Tertiary (K (KT) transition:T) transition:– Dinosaurs disappear “instantaneously” 65 myr agoDinosaurs disappear “instantaneously” 65 myr ago

• Meteorite eventMeteorite event– Luis and Walter Alvarez: transition rich in Luis and Walter Alvarez: transition rich in iridiumiridium (Ir), like in meteorites (Ir), like in meteorites– High KHigh KT Ir the same around the worldT Ir the same around the world– High abundances of osmium, gold and platinumHigh abundances of osmium, gold and platinum– Shocked quartz: formed at high temperature and pressureShocked quartz: formed at high temperature and pressure– Spherical rock droplets: molten rock solidifies in airSpherical rock droplets: molten rock solidifies in air– Soot (some sites): widespread firesSoot (some sites): widespread fires– 200 km crater in Yucat200 km crater in Yucatáán peninsula: 10 km meteoriten peninsula: 10 km meteorite

• Mass extinctionMass extinction– ~10~1088 hydrogen bombs hydrogen bombs– Tidal wave up most of low-lying North AmericaTidal wave up most of low-lying North America– Forest fires worldwide Forest fires worldwide harsh winter harsh winter plants die plants die lack of food lack of food– Acid rain Acid rain kill life in the oceans too kill life in the oceans too– 99% of all living died, 75% of all species became extinct99% of all living died, 75% of all species became extinct

Other Mass ExtinctionsOther Mass Extinctions

• Multiple mass extinctionsMultiple mass extinctions– At least 5 big onesAt least 5 big ones– Many smaller onesMany smaller ones– Event like KEvent like KT every ~100 myrT every ~100 myr– Old seafloor craters would be gone by nowOld seafloor craters would be gone by now– Nearby supernova explosions also every ~ 100 myrNearby supernova explosions also every ~ 100 myr– Magnetic reversals every few myr remove cosmic-Magnetic reversals every few myr remove cosmic-

ray protection of the magnetosphereray protection of the magnetosphere

• EvolutionEvolution– Catastrophes create opportunities, not just disasterCatastrophes create opportunities, not just disaster– May have more effect than gradual evolutionMay have more effect than gradual evolution

Continuing Impact ThreatContinuing Impact Threat

• Impact objectsImpact objects– MeteorMeteor: small (<1 cm), ~ 25 million per day, burn : small (<1 cm), ~ 25 million per day, burn

in atmospherein atmosphere– FireballFireball (not UFO): medium (10 cm (not UFO): medium (10 cm 1 m), explode 1 m), explode

in the atmospherein the atmosphere– MeteoriteMeteorite: large (> few m), vaporizes solid rock, : large (> few m), vaporizes solid rock,

leaving a craterleaving a crater– Tunguska meteorite (1908): <30 m, energy of Tunguska meteorite (1908): <30 m, energy of

several atomic bombs, sound heard round the several atomic bombs, sound heard round the globe, no crater (comet?)globe, no crater (comet?)

• FutureFuture– Probability declines rapidly with sizeProbability declines rapidly with size– Currently able to detect threat, but not divert itCurrently able to detect threat, but not divert it

Moth Camouflage - Moth Camouflage - SelectionSelection

Genetic Drift:BottleneckFounder Effect

Bottleneck

Founder Effect

Phylogeny and Molecular Phylogeny and Molecular EvolutionEvolution• The history of the genes can provide us with The history of the genes can provide us with

information about the structure and function, and information about the structure and function, and significance of a gene or family of genessignificance of a gene or family of genes

• We can also use the reconstructed history to test We can also use the reconstructed history to test hypotheses about evolution itself:hypotheses about evolution itself:– Rates of changeRates of change– The degree of changeThe degree of change– Implications of change, etcImplications of change, etc

• We can then pose and test hypotheses about the We can then pose and test hypotheses about the evolution of phenomena unrelated to the genesevolution of phenomena unrelated to the genes– Evolution of flight in insectsEvolution of flight in insects– Evolution of humansEvolution of humans– Evolution of diseaseEvolution of disease

Assumptions made by phylogenetic Assumptions made by phylogenetic methods:methods:

• The sequences are correctThe sequences are correct

• The sequence are homologousThe sequence are homologous

• Each position is homologousEach position is homologous

• The sampling of taxa or genes is sufficient to resolve The sampling of taxa or genes is sufficient to resolve the problem of interestthe problem of interest

• Sequence variation is representative of the broader Sequence variation is representative of the broader group of interestgroup of interest

• Sequence variation contains sufficient phylogenetic Sequence variation contains sufficient phylogenetic signal (as opposed to noise) to resolve the problem signal (as opposed to noise) to resolve the problem of interestof interest

• Each position in the sequence evolved independentlyEach position in the sequence evolved independently