evolution and darwin

EvolutionEvolutionandand

DarwinDarwin

EvolutionEvolution

• The processesprocesses that have transformed life on earth from it’s earliest formsearliest forms to the vast diversitydiversity that characterizes it today.

• A changechange in the genes!!!!!!!!genes!!!!!!!!

Old Theories of EvolutionOld Theories of Evolution

• Jean Baptiste LamarckJean Baptiste Lamarck (early 1800’s) proposed:

““The inheritance of acquired characteristics”The inheritance of acquired characteristics”

• He proposed that by using or not using its body parts, an individual tends to developdevelop certain characteristicscharacteristics, which it passespasses on to its offspringoffspring.

““The Inheritance of Acquired The Inheritance of Acquired Characteristics”Characteristics”

• Example:Example:

A giraffe acquired its long neck because its ancestor stretched higher and higher into the trees to reach leaves, and that the animal’s increasingly lengthened neck was passed on to its offspring.

Charles DarwinCharles Darwin

• Influenced by Charles LyellInfluenced by Charles Lyell who published “Principles of Geology”.“Principles of Geology”.

• This publication led DarwinDarwin to realize that natural forces gradually change Earth’s surface and that the forces of the past are still operating in modern times.


• Darwin set sail on the H.M.S. BeagleH.M.S. Beagle (1831-1836) to survey the south seas (mainly South America and the Galapagos Islands)(mainly South America and the Galapagos Islands) to collect plants and animals.

• On the Galapagos Islands, Galapagos Islands, Darwin observed species that lived no where else in the world.– Patterns of diversity, e.g., Pinta, Isabela and Hood island tortoises that ate

vegetation, birds (finches) on Galapagos islands• Far more species than previously known • Similar ecosystems did not have same species • Species adapted to their habitat• Fossils – preserved remains of ancient organism

• These observations led Darwin to write a book.


• Wrote in 1859Wrote in 1859: “On the Origin of Species by “On the Origin of Species by Means of Natural Selection”Means of Natural Selection”

• Two main points:Two main points:

1.1. Species were not created in their present Species were not created in their present form, but evolved from ancestral species.form, but evolved from ancestral species.

2.2. Proposed a mechanism for evolution:Proposed a mechanism for evolution: NATURAL SELECTIONNATURAL SELECTION

Natural SelectionNatural Selection• IndividualsIndividuals with favorablefavorable traitstraits are more

likely to leave more offspring better suited for their environmentenvironment.

• Also known as “Differential Reproduction”“Differential Reproduction”


English peppered moth (English peppered moth (Biston betularia))

- light and dark phases- light and dark phases

http://tidepool.st.usm.edu/crswr/peppermoths.html

Peppered moths rest on trees and depend Peppered moths rest on trees and depend on camouflage for protection.on camouflage for protection.

Evolution by Natural Selection•

Evolution by Natural Selection – Struggle for existence – competition for resources – Survival of the fittest (natural selection)– Fitness is a

result of adaptations

• Adaptation – any inherited characteristic that increases an organism’s chance of survival

• Types of adaptation-

– Camouflage – Mimicry – one species resembles another – Antimicrobial resistance

Darwin’s Beliefs About Descent• Descent with modification – over long periods

of time, natural selection produces organisms that have different structures, niches or occupy different habitats. Each species has descended with changes from other species over time.

• Common descent – all living and extinct species were derived from common ancestors

Artificial SelectionArtificial Selection• Artificial selection – nature provides the

variation, but humans select the variations they find useful, e.g. breeding the largest hogs, fastest horses – The selective breedingselective breeding of domesticated plants and animals

by man.

• Question:Question:What’s the ancestor of the domesticated dog?

• Answer:Answer: WOLFWOLF

Evidence of EvolutionEvidence of Evolution1.1. Biogeography: Biogeography:

Geographical distribution of species.Geographical distribution of species.

Convergent Evolution - Convergent Evolution - similar similar environments leads to unrelated species with environments leads to unrelated species with similar traitssimilar traits

2. Fossil Record:2. Fossil Record:

Fossils and the order in which they appear Fossils and the order in which they appear in layers of sedimentary rock in layers of sedimentary rock (strongest (strongest evidence).evidence).

Evidence of EvolutionEvidence of Evolution

3. Comparative anatomy3. Comparative anatomyHomologous structures: Structures Homologous structures: Structures that are similar because ofthat are similar because of

common ancestry common ancestry Vestigal structures: Vestigal structures: traces of traces of

homologous organs in other specieshomologous organs in other species

Evidence of EvolutionEvidence of Evolution

4. Comparative embryology:4. Comparative embryology:

Study of structures that appear Study of structures that appear during during embryonic development.embryonic development.

5. Molecular biology:5. Molecular biology:

DNA and proteins (amino acids)DNA and proteins (amino acids)

6. Experimental evidence6. Experimental evidence

Population GeneticsPopulation Genetics

• The sciencescience of genetic changegenetic change in population.

PopulationPopulation

• A localized group of individualsindividuals belonging to the same speciessame species.

SpeciesSpecies

• A group of populationspopulations whose individualsindividuals have the potential to interbreedinterbreed and produce viableviable offspring.

Gene PoolGene Pool

• The total collection of genescollection of genes in a population at any one time.

Genetics and Evolution

• Relative frequency – number of times an allele is present in a gene pool, compared to the number of times other alleles for the same gene are present o EX: Black (B) fur 40% and b fur 60% in mice o In genetic terms, evolution is the change in relative frequency of alleles in a population o May not match Mendelian ratios

• Sources of genetic variation o Mutations – change in sequence of DNA o Gene shuffling – different combinations of genes during gamete production and crossing over

• Single gene and polygenic traits o Natural selection on single gene traits can lead to changes in allele frequencies and thus evolution (Ex: lizard color, red easy to see and black keeps lizard warmer, reduction in normal brown which has no advantage) o Polygenic – Natural selection is more complex and can affect distributions of phenotypes in 3 modes of action

Modes of ActionModes of Action

• Natural selectionNatural selection has three modesthree modes of action:

1.1. Stabilizing selectionStabilizing selection

2.2. Directional selectionDirectional selection

3.3. Diversifying selectionDiversifying selection

Number ofIndividuals

Size of individualsSmall Large

1.1. Stabilizing SelectionStabilizing Selection

• ActsActs upon extremesextremes and favorsfavors the intermediateintermediate.



2.2. Directional SelectionDirectional Selection

• FavorsFavors variants of one extremeone extreme.



3.3. Diversifying SelectionDiversifying Selection

• FavorsFavors variants of opposite extremesopposite extremes.



Hardy-Weinberg PrincipleHardy-Weinberg Principle

• The conceptconcept that the shuffling of genesshuffling of genes that occur during sexual reproduction, by itself, cannot changecannot change the overall genetic makeup of a population.


• This principleprinciple will be maintained in nature only if all fivefive of the following conditions are met:

1.1. Very large populationVery large population

2.2. Isolation from other populationsIsolation from other populations

3.3. No net mutationsNo net mutations

4.4. Random matingRandom mating

5.5. No natural selectionNo natural selection


• Remember:Remember:

If these conditions are met, the population is at equilibriumequilibrium.

• This means “No Change” or “No “No Change” or “No Evolution”.Evolution”.

MacroevolutionMacroevolution

• The origin of taxonomic groups higher higher than the species levelthan the species level.

MicroevolutionMicroevolution

• A change in a population’s gene poolpopulation’s gene pool over a secession of generations.

• Evolutionary changesEvolutionary changes in species over relatively brief periods of geological timegeological time.

Five Mechanisms of MicroevolutionFive Mechanisms of Microevolution

1. Genetic drift:1. Genetic drift:

Change in the gene pool of a Change in the gene pool of a small small population due to chance.population due to chance.

• Two examples:Two examples:

a. Bottleneck effecta. Bottleneck effect

b. Founder effectb. Founder effect

a. Bottleneck Effecta. Bottleneck Effect

• Genetic driftGenetic drift (reduction of alleles in a population) resulting from a disasterdisaster that drastically reduces reduces population sizepopulation size.

• Examples:Examples:

1.1. EarthquakesEarthquakes

2.2. Volcano’sVolcano’s

b. Founder Effectb. Founder Effect

• Genetic driftGenetic drift resulting from the colonizationcolonization of a new location by a small number of individuals.

• Results in random changerandom change of the gene pool.


1.1. Islands (first Darwin finch)Islands (first Darwin finch)


2. Gene Flow:2. Gene Flow:

TThe gain or loss of allelesgain or loss of alleles from a population by the movementmovement of individuals or gametes.

• Immigration or emigrationImmigration or emigration.


3. Mutation:3. Mutation:

Change in an organism’s DNA thatChange in an organism’s DNA thatcreates a new allele.creates a new allele.

4. Non-random mating:4. Non-random mating:

The selection of mates other thanThe selection of mates other thanby chance.by chance.

5. Natural selection:5. Natural selection:

Differential reproduction.Differential reproduction.

SpeciationSpeciation

• The evolutionevolution of new species.

Reproductive BarriersReproductive Barriers

• Any (isolation) mechanismmechanism that impedesimpedes two species from producing fertile and/or viable fertile and/or viable hybrid offspringhybrid offspring.

• Two barriers:Two barriers:

1.1. Pre-zygotic barriersPre-zygotic barriers

2.2. Post-zygotic barriersPost-zygotic barriers

1.1. Pre-zygotic BarriersPre-zygotic Barriers

a. Temporal isolation:a. Temporal isolation:

Breeding occurs at different times for different species.

b. Habitat isolation:b. Habitat isolation:

Species breed in different habitats.

c. Behavioral isolation:c. Behavioral isolation:

Little or no sexual attraction between species.

1.1. Pre-zygotic BarriersPre-zygotic Barriers

d. Mechanical isolation:d. Mechanical isolation:

Structural differences prevent gamete exchange.

e. Gametic isolation:e. Gametic isolation:

Gametes die before uniting with gametes of other species, or gametes fail to unite.

2.2. Post-zygotic BarriersPost-zygotic Barriers

a. Hybrid inviability:a. Hybrid inviability:

Hybrid zygotes fail to develop or fail to reach sexual maturity.

b. Hybrid sterility:b. Hybrid sterility:

Hybrid fails to produce functional gametes.

c. Hybrid breakdown:c. Hybrid breakdown:

Offspring of hybrids are weak or infertile.

Allopatric SpeciationAllopatric Speciation

• Induced when the ancestralancestral population becomes separatedseparated by a geographical geographical barrier.barrier.


Grand Canyon and ground squirrels

Adaptive RadiationAdaptive Radiation

• Emergence of numerous speciesEmergence of numerous species from a common ancestorcommon ancestor introduced to new and diverse environments.


Darwin’s FinchesDarwin’s Finches

Sympatric SpeciationSympatric Speciation

• Result of a radical change in the genome that produces a reproductively isolated sub-reproductively isolated sub-populationpopulation within the parent population (rare).

• Example: Plant evolution - polyploidExample: Plant evolution - polyploid

A species doubles it’s chromosome #chromosome # to become tetraploid.

reproductive sub-population

Parent population

Interpretations of SpeciationInterpretations of Speciation

• Two theories:Two theories:

1.1. Gradualist Model (Neo-Darwinian):Gradualist Model (Neo-Darwinian):

Slow changes in species overtime.

2.2. Punctuated Equilibrium:Punctuated Equilibrium:

Evolution occurs in spurts of relatively rapid change.

Convergent EvolutionConvergent Evolution

• SpeciesSpecies from different evolutionary branchesevolutionary branches may come to resemble one another if they live in very similar environments.very similar environments.


1.1. Ostrich (Africa) and Emu (Australia).Ostrich (Africa) and Emu (Australia).

2.2. Sidewinder (Mojave Desert) andSidewinder (Mojave Desert) and

Horned Viper (Middle East Desert)Horned Viper (Middle East Desert)

CoevolutionCoevolution

• Evolutionary changeEvolutionary change, in which one species act as a selective forceselective force on a secondsecond species, inducing adaptations that in turn act as selective force on the firstfirst species.


1.1. Acacia ants and acacia treesAcacia ants and acacia trees

2.2. Humming birds and plants with Humming birds and plants with flowers flowers with long tubeswith long tubes

Fossils

• Fossil - traces and preserved remains of ancient life, formed in sedimentary rock

• Types of fossils– Trace - indirect evidence, e.g., footprints– Mold – impression b of an organism– Cast – mold filled with sediment – Replacement – original organism replaced with mineral crystals– Petrified – empty pore spaces filled with minerals, e,g petrified wood– Amber – preserved tree sap traps organism

– Original material – mummified or frozen

How Are Fossils Dated?• Relative dating – age of a fossil is determined by

comparing placement with that of fossils in other layers of rock– Index species – compared with other fossils because

they are easily recognized, lived for a short time and had wide geographic range

• Radioactive dating – use radioactive decay to assign absolute ages to rocks– Half life – length of time required for half of the

radioactive atoms in a sample to decay

Early history of life• Solar system~ 12 billion years

ago (bya)• Earth~ 4.5 bya• Life~ 3.5 to 4.0 bya• Prokaryotes~ 3.5 to 2.0 bya

stromatolites• Oxygen accumulation~ 2.7 bya

photosynthetic cyanobacteria• Eukaryotic life~ 2.1 bya• Muticelluar eukaryotes~ 1.2

bya• Animal diversity~ 543 mya• Land colonization~ 500 mya

The Origin of Life• Old theory of origin of life

– spontaneous generation (from non-living)• Theory of biogenesis (life from life) – Redi, Pasteur Early Atmosphere - hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide and water

Early Life

• How did first cells (bacteria) form? – Protenoid microspheres – large organic

molecules form tiny bubbles– First life anaerobic, living in the oceans

• Microfossils (microscopic) 3.5 billion years old, when little oxygen in atmosphere

• By 2.2 billion years, fossil evidence of microfossils that were photosynthetic

Organic monomers/polymer synthesis

• Miller/Urey experiment:

• Water, hydrogen, methane, ammonia

• No oxygen

• All 20 amino acids, nitrogen bases, & ATP formed

The Endosymbionic Theory

• Mitochondria and chloroplasts were formerly from small prokaryotes living within larger cells (Margulis)

Evidence of The Endosymbionic Theory

• Mitochondria and chloroplasts – DNA is similar to prokaryotic DNA– Have their own ribosomes– Can undergo binary fission

evolution and darwin

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