EvolutionEvolutionandand

DarwinDarwin

What is evolution?

• A slow change over time

• The development of new types of organisms from preexisting types of organisms over time

• A heritable change in the characteristics within a population from one generation to the next

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Evolution Primers

• Isn't Evolution Just a Theory???

History of Evolution

Charles Darwin – a brief history

• Born in England on February 12, 1809

• In 1831 began a 5-year journey on the HMS Beagle as a naturalist

• Observations and specimen collections led him to develop “the single best idea anyone has ever had”

• “Developed a scientific theory of biological evolution that explains how modern organisms evolved over long periods of time through descent from common ancestors”

• Darwin video clip

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

• These observations led Darwin to write a book.

Darwin’s Observations

1.Species vary globally1.Species vary globally – Darwin noticed that different, yet ecologically similar, animal species inhabited separated, but ecologically similar habitats around the globe– Flightless birds (emu, ostrich, rhea)– Convergent evolution

Darwin’s Observations

2. Species vary locallySpecies vary locally – Darwin noticed that different, yet related, animal species often occupied different habitats within a local area– Tortoise, mockingbirds

Darwin’s Observations

3. Species vary over timeSpecies vary over time – Darwin noticed that some fossils of extinct animals were similar to living species- fossils – preserved remains of ancient, extinct organisms

Who is Charles Darwin?

Friends

• Friends Evolution Montage

Ideas that Shaped Darwin’s Ideas that Shaped Darwin’s ThinkingThinking

• Lyell & Hutton – – Concluded that Earth is extremely old and that the

processes that changed Earth in the past are the same processes that operate in the present (still changing)

– Hutton (in 1785) – geological processes shape Earth– Lyell (in 1830) – uniformitarianism – geological

processes we see in action today must be the same ones that shaped Earth millions of years ago

• Lamarck – 1809– Inheritance of Acquired Characteristics – Organism could change during their lifetimes by

selectively using or not using various parts of their bodies; then pass these acquired traits on to their offspring, enabling species to change over time

– One of the first naturalist to suggest that species are not fixed

– One of the first to try and explain evolution scientifically using natural processes

– Recognized that there is a link between an organism’s environment and it’s body structures

““The Inheritance of Acquired The Inheritance of Acquired Characteristics”Characteristics”Lamarck vs Darwin

• 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.-A muscle builder will pass the muscles on to his offspring…. NOT TRUENOT TRUE

Ideas that Shaped Darwin’s Ideas that Shaped Darwin’s ThinkingThinking

• Malthus – 1798– English economist– Reasoned that if the human

population grew unchecked, there would not be enough living space and food for everyone

• Artificial Selection– Nature provides variations, but

humans select those they find useful

Artificial SelectionArtificial Selection

• The selective breedingselective breeding of domesticated plants and animals by man.

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

• Answer:Answer: WOLFWOLF• This is STELLA!!!!!This is STELLA!!!!!

Darwin’s Contribution to Darwin’s Contribution to ScienceScience

Darwin developed a scientific theory of biological evolution that explains how modern organisms evolved over long periods of time through descent of common ancestors.

Darwin and Wallace

• Same conclusion about evolution as a result of similar experiences– Influenced by Lyell and Malthus– Observed plant and animal life in several

parts of the world– Wallace (1858) sent Darwin a manuscript

describing “natural selection”– Wallace and Darwin arrived at the theory of

Natural Selection independently, and presented their ideas in public together in 1858

Charles DarwinCharles DarwinWallace kind of gets dissedWallace kind of gets dissed

• Wrote in 1859Wrote in 1859: (11/24 – pub)• ““On the Origin of Species by Means of On the Origin of Species by Means of

Natural Selection”Natural Selection”• Main points:Main points:

1. Struggle for Existence (competition)1. Struggle for Existence (competition)

2. Variation and Adaptation2. Variation and Adaptation

3. Survival of the Fittest3. Survival of the Fittest

44. Natural SelectionNatural Selection

Struggle for ExistenceStruggle for Existence

• Organisms produce more offspring than can survive. (OVERPRODUCTION)– Grasshoppers can lay more than 200

eggs at a time. Only a small fraction of these offspring survive to reproduce.

Variations and Variations and AdaptationsAdaptations

• There is variation in nature, and certain variations – called adaptations – increase an individual’s chance of surviving and reproducing. – Physical, physiological, and/or behavioral

traits that enhance an organisms chances for surviving in its environment

• Green vs. yellow color in grasshoppers is a heritable variation: green can blend into environment and avoid predators

Survival of the FittestSurvival of the Fittest

• Suggests that natural selection selects mainly for survival… IT DOES NOT

• Selects for contribution of genes to future generations– Reproduction resulting in viable offspring– Selects for individuals that are able to

produce the greatest number of offspring, that in turn, can survive and reproduce

• Green grasshoppers have higher fitness and so survive and reproduce more often than yellow

Natural Selection

• How Does Evolution Really Work?

Survival of the Sneakiest

• Survival of the Sneakiest

• Will the grey mouse or white mouse survive more easily?

• Why?

• What characteristic is affecting the fitness of the mice?

• Peppered Moths:In the year 1848, 5% of the population was dark colored moths while 95% was light colored.

• In the year 1895, 98% was dark colored while 2% was light colored.

• In the year 1995, 19% was dark colored while 81% was light colored.

• What was the reason for the changes in the number of dark and light colored moths?

• In the early 1800s, England was not so industrialized yet and pollution was still low. The trees had light colored bark so the light colored moths had a better advantage and a better survival rate than dark colored ones.

• In the late 1800s, England started to become more industrialized and factories increases. These factories caused trees to become soot coated, the bark was darker. The dark colored moths were then camouflaged and survived more than light colored ones.

• Then in the mid 1900s, the air started to become cleaner due to clean air laws. Trees began to have light colored barks and once again light colored moths increased in the population.

Year Dark Light

1848 5% 95%

1895 98% 2%

1995 19% 81%

Another example of natural selection…

• http://www.sciencenetlinks.com/interactives/evolution.html

Darwin’s Finches– A Close Look at Darwin’s Finches

When Charles Darwin traveled to the Galápagos Islands, he found a variety of species of finches. Although each species was slightly different from the others, all the species were related. None of the finch species he found were similar to finches on the mainland.

When Darwin saw such extensive diversity of species in a single group of birds, he hypothesized that they all could have descended from a common ancestor. His observations of these finches helped him formulate his concept of evolution.

The phylogenetic tree below shows the relationships Darwin proposed among the species of finches. The tree is based on a comparison of the anatomy, behavior, and location on the island of each finch species. Look carefully at each species, and notice the dramatic difference among the beaks. Each type of finch has a beak adapted to its diet.

Darwin’s finches are an example of adaptive radiation. Adaptive radiation is the emergence of many species from a common ancestor that was introduced to various new environments. For adaptive radiation to occur, the new environments must offer new opportunities and pose new problems of survival for the species.1. Which of the ground finches illustrated above would be able to eat the

largest, toughest nuts and seeds? Explain your answer.

2. Study the insect-eating finches shown in the diagram. What can you infer about the insects of the Galápagos Islands?

What does Darwin’s mechanism What does Darwin’s mechanism for evolution suggest about living for evolution suggest about living

and extinct species???and extinct species???• All organism descended from a

common ancestor• “Descent with modification”• Homer Evolution

Evidence for Evolution

• Biogeography• Fossil Record• Comparative Anatomy• Developmental Biology• Comparative Biochemistry• How Do We Know Evolution Happens

?

Biogeography – study of where organisms live now and where they and their ancestors lived in the past

• Patterns in the distribution of living and fossil species tell us how modern organisms evolved from their ancestors– Closely related species

differentiate in slightly different climates

– Very distantly related species develop similarities in similar environments

Adaptive RadiationAdaptive Radiation• Evolutionary process that

gives rise to new species adapted to new habitats and ways of life

The Age of the Earth and The Age of the Earth and FossilsFossils

– The Age of the Earth • Earth had to be old enough for these

proposed changes to occur – plenty of time for Natural Selection

• Earth is ~4.5 byo (determined by radioactive dating) – plenty of time for natural selection to take place

– Fossils discovered after Darwin fill in some of the “gaps” in the fossil record

– One fossil shows the evolution of whales from a land-based mammal (book figure 16-3)

Comparing Anatomy and EmbryologyComparing Anatomy and Embryology• Homologous StructuresHomologous Structures

– Parts that are similar in structure but different in function

– Humans, penguins, alligators, bats all have the same bones in their arms but they are used for different things

• Similar EmbryosSimilar Embryos– Embryos of different

organisms are very similar and have similar structures early on

– Must have similar proteins at work

• Vestigial StructuresVestigial Structures– Structures that are so

reduced in size or function that they are merely traces of similar organs in other species (I.e. tailbone and appendix in humans)

• Analogous Analogous StructuresStructures– Parts that are

similar in function but not structure

– i.e. Wing of bee, bird, bat

Genetics and Molecular Genetics and Molecular BiologyBiology

• All organisms have DNA– Therefore similar RNA, similar genes,

and similar proteins

• All organisms have ATP

Evolution of Populations Evolution of Populations Ch 17Ch 17

• Process of change over time

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

Population GeneticsPopulation Genetics

• The sciencescience of genetic changegenetic change in population.

• Population – all the members of a species that occupy a particular area at the same time

• Gene Pool – all the genes in all the members of a population

Genes and Variation• Genetics Joins Evolutionary Theory

– Variation is the raw material for natural selection– Gene pool – consists of all the genes, including all the different

alleles for each gene, that are present in a population– Relative frequency – the number of times that the allele occurs in

a gene pool, compared with the number of times other alleles for the same gene occur

– Therefore – evolution is any change in the relative frequency of alleles in the gene pool of a population over time

• 3 Sources of Genetic Variation – Mutations– Genetic Recombination in Sexual Reproduction (Ind assortment

and crossing over)– Lateral Gene Transfer (conjugation)

• Single-Gene (2 pheno) vs. Polygenic Traits (many pheno/bell curve)

***Natural Selection acts directly on PHENOTYPESNatural Selection acts directly on PHENOTYPES not actual alleles*** some phenotypes are better suited to an environment than others and they will survive, reproduce and pass on their genes.

Evolution as Genetic Change in Populations

Stabilizing SelectionIndividuals with the average form of a trait have the highest fitnessRepresents the optimum for most traitsResults in a similar morphology between most members of the species

Directional SelectionIndividuals that display a more extreme form of a trait have greater fitness than individuals with an average form of the traitA shift in one directionPeppered moth

Disruptive SelectionIndividuals with either extreme variation of a trait have greater fitness than individuals with the average form of the traitA shift in both direction, away from the centerShell color (dark rocks and light sand)

How Natural Selection Works – 3 Types

Genetic DriftGenetic Drift

• Random changes in the frequency Random changes in the frequency of a gene in the absence of natural of a gene in the absence of natural selection selection occurs because of occurs because of CHANCECHANCE

• Occurs efficiently in Occurs efficiently in smallsmall populations because small changes populations because small changes affect more membersaffect more members

• Two examples:Two examples:a. Bottleneck effecta. Bottleneck effectb. Founder effectb. Founder effect

Genetic Drift

a. a. Bottleneck EffectBottleneck Effect

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

• Example:Example:1.1. IslandsIslands

(first Darwin finch)(first Darwin finch)

Hardy-Weinberg Hardy-Weinberg PrinciplePrinciple

• Genetic EquilibriumGenetic Equilibrium – situation in which allele frequencies in the gene pool of a population remain constant

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

• Shows mathematically and theoretically that there are situations where evolution DOES NOT OCCUR– Seldom achieved in nature

Hardy-Weinberg Hardy-Weinberg PrinciplePrinciple• 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 populations Isolation from other populations (no immigration, no emigration)(no immigration, no emigration)

3.3. No net mutationsNo net mutations

4.4. Random matingRandom mating

5.5. No natural selectionNo natural selectionHardy-Weinberg Principle

SpeciesSpecies

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

SpeciationSpeciation

• The evolutionevolution of new species. Species that occupy an otherwise unoccupied niche face no competition, they will therefore have a 100% success rate

Reproductive Isolation Reproductive Isolation

• Any mechanismmechanism that impedesimpedes two species from producing fertile and/or viable hybrid fertile and/or viable hybrid offspring offspring -factor necessary for the -factor necessary for the formation of a formation of a new species new species.

• Barriers:Barriers:11.. GeographicGeographic (rivers, mountains) (rivers, mountains)2.2. BehavorialBehavorial - differences in courtship - differences in courtship

behavior behavior 3. 3. TTemporalemporal - fertile periods ( - fertile periods (ttime)ime)

Interpretations of Interpretations of SpeciationSpeciation

• Two theories:Two theories:

1. Gradualist Model 1. Gradualist Model (Neo-Darwinian):(Neo-Darwinian):

Slow Slow changes in species overtime.

2. Punctuated 2. Punctuated Equilibrium:Equilibrium:Evolution occurs in spurts of relatively rapid change.

MacroevolutionMacroevolution

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

Adaptive RadiationAdaptive Radiationaka Divergent Evolutionaka Divergent Evolution

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

• Example:Example:

Darwin’s FinchesDarwin’s Finches

Darwin’s Finches an example of Darwin’s Finches an example of Adaptive RadiationAdaptive Radiation

Convergent EvolutionConvergent Evolution

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

• Example:Example: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)3. Shark and Dolphin3. Shark and Dolphin

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.

• Example:Example:

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

Radiometric Dating– When unstable nuclei

release particles or radiant energy until the nuclei becomes stable

– Half-life = The length of time it takes for one-half of a sample to decay to stable form

The Age of the Earth and

Fossils– Fossils

• Trace the evolution of modern species from ancient/extinct ancestors

• Relative dating vs.• Absolute dating

The Earth is born…

Date Event Additional Info

4.6 bya

Earth was born

4 bya Cooling of Earth, 1st solid rocks formed on earth’s surface

4-3.8 bya

Volcanic activity & meteorites release gases that produce earth’s atmosphere

Contained H2O vapor, CO, CO2, H2, N2, NH3, CH4

It did NOT contain oxygen

3.8 bya

Cooling continues, water appears, beginning of oceans

Earth cool enough for liquid to stay on the ground

3.5 bya

Age of first prokaryotic microfossils Heterotrophic – obtained nutrients from organic “soup”Anaerobic – able to live in oxygen-free environment

3.4 bya

Appearance of 1st autotrophs Organic soup begins to run outPhotosynthesis begins – using H2S instead of water

2.2 bya

Introduction of oxygen into the atmosphereMore modern form of photosynthesis appeared

Used H2O instead of H2SCaused earth to cool as they converted CO2 O2

Led to aerobic respirationOzone layer protection

1.6-1.1 bya

1st eukaryotic cells evolved

Sexual reproduction evolvedMulticellular organisms arose

Nucleus contains DNA, have membrane bound organelles, etc.Increased the speed of evolutionIncreased genetic variation

1700s Spontaneous Generation (abiogenesis) – idea that life comes from non-life

Disproven through Redi, Spallanzani, & Pastuer

1953 Miller & Urey mix methane, water, ammonia, and hydrogen with energy (sun & lightning) Primordial Soup

Amino acidsAmino acids & other organic compounds are produced as by-productsProvide glimpse at how molecules (proteins) may 1st have formed on the Earth

The Age of the Earth and The Age of the Earth and FossilsFossils

– The Age of the Earth • Earth had to be old enough for these

proposed changes to occur• Earth is ~4.5 byo (determined by

radioactive dating)

History of Earth (24hours)12:00am – Earth is formed

5:00am – Prokaryotes appear4:00pm – Eukaryotes appear10:00pm – Invasion of land

11:59:30pm – Humans appear

Miller/Urey Experiment and Primordial Soup

• Oparin and Haldane: hypothesized that the early atmosphere was composed of: ammonia (NH3), hydrogen gas (H2), water vapor (H20), and compounds made of carbon and hydrogen, like methane (CH4). They thought that at high temperatures, simple organic compounds (like amino acids) could form. When earth cooled, and lakes and oceans formed, theses simple compounds could be found in the water and enter complex chemical reactions fueled by lightning and ultraviolet violet radiation resulting in macromolecules essential to life like proteins.

• Miller and Urey: 1953 set up an apparatus to test Oparin’s hypotheses. Their experiment produced a variety of organic compounds, including amino acids

EndosymbioticTheory• What is the theory of

endosymbiosis? Theory that large prokaryotic, unicellular organisms engulfed (ate) smaller prokaryotic, unicellular organisms. Engulfed prokaryotes eventually gave rise to modern mitochondria and chloroplasts.

• What evidence supports the hypothesis that mitochondria and chloroplasts were once free living prokaryotic cells? Replicate independently and replicate like prokaryotes (binary fission), have their own DNA and their own ribosomes (also similar to DNA and ribosomes of prokaryotes)