History of Evolutionary History of Evolutionary TheoryTheory

Anaximander to Austrian MonksAnaximander to Austrian Monks

The Evolutionary ModelThe Evolutionary Model

Evolution is based on two models of population Evolution is based on two models of population changechange

Mutation—Change In DNA Structure—involves the Mutation—Change In DNA Structure—involves the creation of new life formscreation of new life forms

Natural selection involves environmental pressures Natural selection involves environmental pressures that favor, restrict, or eliminate life formsthat favor, restrict, or eliminate life forms

Other factors may favor population change: gene Other factors may favor population change: gene flow (migration) or genetic drift (changes as the flow (migration) or genetic drift (changes as the product of chanceproduct of chance

Overview of Evolutionary ChangeOverview of Evolutionary Change

First, we look at the history of evolutionary thought First, we look at the history of evolutionary thought from the Greek philosophers to the Darwinist modelfrom the Greek philosophers to the Darwinist model

Then we look at the mechanisms of evolutionary Then we look at the mechanisms of evolutionary changechange

Biological, Molecular, and Population GeneticsBiological, Molecular, and Population Genetics Natural SelectionNatural Selection Other Mechanisms of Population ChangeOther Mechanisms of Population Change Speciation and TaxonomySpeciation and Taxonomy

Overview of Evolution of Overview of Evolution of Evolutionary ThoughtEvolutionary Thought

History of Evolutionary ConceptsHistory of Evolutionary Concepts Greek PrecursorsGreek Precursors 1717thth Century Theologians Century Theologians 1818thth Century Catastrophists Century Catastrophists 1818thth Century Uniformitarians Century Uniformitarians Uniformitarianism of Hutton and LyellUniformitarianism of Hutton and Lyell Darwin and WallaceDarwin and Wallace Gregor MandelGregor Mandel Key concepts in evolutionary historyKey concepts in evolutionary history Essentialism/Chain of BeingEssentialism/Chain of Being Natural Selection/MutationNatural Selection/Mutation

Early Theorists: The Classical Early Theorists: The Classical GreeksGreeks

Anaximander:Anaximander: (6 (6thth Century BC) Century BC) Argued that men arose from fishes, setting the stage Argued that men arose from fishes, setting the stage

of of He relied on reasoning, not supernatural explanationsHe relied on reasoning, not supernatural explanations Plato and Aristotle:Plato and Aristotle: Set the stage for two models of Set the stage for two models of

existenceexistence Essentialism, or the ideal type of biological lifeformsEssentialism, or the ideal type of biological lifeforms Great Chain of Being, which placed all lifeforms in a Great Chain of Being, which placed all lifeforms in a

hierarchical system of existence from lowest to hierarchical system of existence from lowest to highest.highest.

Early Models: EssentialismEarly Models: Essentialism Essentialism: The ideal reality against which Essentialism: The ideal reality against which

the perceived reality is compared and the perceived reality is compared and contrastedcontrasted

Plato (above) was the first to come up with the Plato (above) was the first to come up with the ideal entity (including the human), against which ideal entity (including the human), against which the perceived entity was compared the perceived entity was compared

Aristotle (below) also accepted the idea of a Aristotle (below) also accepted the idea of a perfect universe, but did not accept the dichotomy perfect universe, but did not accept the dichotomy that Plato posited. Rather, he saw the essential as that Plato posited. Rather, he saw the essential as the properties of each lifeform and other entities. the properties of each lifeform and other entities.

Greek gods and goddesses represented the ideal Greek gods and goddesses represented the ideal human male and female forms, as reflected in human male and female forms, as reflected in sculpture and other representational art.sculpture and other representational art.

Any deviation from the essential reflected some Any deviation from the essential reflected some defect in any lifeform, animal or plant. defect in any lifeform, animal or plant.

Early Models: The Great Chain of Early Models: The Great Chain of BeingBeing A hierarchy of entities from the A hierarchy of entities from the

simplest to most complex simplest to most complex anticipated the later rise of anticipated the later rise of taxonomy; Karl von Linntaxonomy; Karl von Linné é (discussed below) drew on this (discussed below) drew on this model.model.

In this view, the human race was In this view, the human race was the most complex and perfect of the most complex and perfect of all living formsall living forms

Humans, however, were below the Humans, however, were below the divine beings (including demons divine beings (including demons in the model depicted here. in the model depicted here.

CatastrophismCatastrophism Earth’s history is product of sudden Earth’s history is product of sudden

changechange Example: Creation of Earth in six Example: Creation of Earth in six

days (upper left), including Adamdays (upper left), including Adam Example: Flood (Noah’s Ark), Example: Flood (Noah’s Ark),

which eliminated all life except which eliminated all life except Noah’s family and the male and Noah’s family and the male and female animals he allowed into the female animals he allowed into the ark ark

Catastrophism does have some basis Catastrophism does have some basis of reality: an asteroid that struck the of reality: an asteroid that struck the earth 65 million years ago (lower earth 65 million years ago (lower left) nearly destroyed all lifeleft) nearly destroyed all life

Early Theorists: 17Early Theorists: 17thth Century Century CatastrophistsCatastrophists

James UssherJames Ussher (1581-1656): Argued that (1581-1656): Argued that humankind created noon, Oct. 23, 4004;(Upper left)humankind created noon, Oct. 23, 4004;(Upper left)

He based his calculations on biblical history and He based his calculations on biblical history and astronomyastronomy

Nicholas StenoNicholas Steno (1638-1686): (1638-1686): Stratigraphy—sediments deposited by water in a Stratigraphy—sediments deposited by water in a

sequencesequence Robert HookeRobert Hooke (1635-1703) (1635-1703) Described fossils (mineralized remains of lifeforms)Described fossils (mineralized remains of lifeforms) Recognized them as of extinct or early formative Recognized them as of extinct or early formative

creatures creatures He also described the cell as the basic unit of life He also described the cell as the basic unit of life

and invented the microscopeand invented the microscope AdaptationAdaptation: creatures changed as earth changed: creatures changed as earth changed All three explained history of earth as a catastrophic All three explained history of earth as a catastrophic

creation.creation.

Early Theorists: 18Early Theorists: 18thth Century Century CatastrophistsCatastrophists

Carolus LinnaeusCarolus Linnaeus (Carl Linn (Carl Linné; 1707-1778) é; 1707-1778) Inventor of Inventor of taxonomytaxonomy—classification of lifeforms based on —classification of lifeforms based on

similarities and differences (Sample taxonomy next slide)similarities and differences (Sample taxonomy next slide) Viewed system as divinely ordainedViewed system as divinely ordained He also classified human races as being of separate species He also classified human races as being of separate species

with their own personality traitswith their own personality traits Georges CuvierGeorges Cuvier (1769-1832) (1769-1832) Developed the science of comparative anatomyDeveloped the science of comparative anatomy Compared the Anatomy of present lifeforms with those of the Compared the Anatomy of present lifeforms with those of the

fossils formsfossils forms Catastrophism: He concluded that the lifeforms of the world Catastrophism: He concluded that the lifeforms of the world

changed but they did not evolvechanged but they did not evolve

Carolus Linnaeus (LinnCarolus Linnaeus (Linné)é)

Early Theorists: 18Early Theorists: 18thth Century Century UniformitariansUniformitarians

UniformitarianismUniformitarianism: Processes occur at same rate : Processes occur at same rate through time—present and pastthrough time—present and past

Georges-Louis LeclercGeorges-Louis Leclerc (Comte de Buffon; 1707- (Comte de Buffon; 1707-1788)1788)

He observed that the tides and currents of seas are He observed that the tides and currents of seas are uniform through timeuniform through time

He concluded that the earth had to be older than 6000 He concluded that the earth had to be older than 6000 yearsyears

James HuttonJames Hutton (1726-1797): Discovered uniformity (1726-1797): Discovered uniformity in 3 processes:in 3 processes:

Deposit of strata under oceansDeposit of strata under oceans Uplifting seabeds to above sea level by volcanic Uplifting seabeds to above sea level by volcanic

actionaction Land erosion by water, wind, and decayLand erosion by water, wind, and decay He too concluded that the earth had to be older than He too concluded that the earth had to be older than

6000 years6000 years

Uniformitarianism According to Charles Uniformitarianism According to Charles LyellLyell

Charles LyellCharles Lyell (1797-1875) (1797-1875) Espoused extreme form of uniformitarianism Espoused extreme form of uniformitarianism

by denying catastrophism (by denying catastrophism (Principles of Principles of GeologyGeology))

Three aspects hold up todayThree aspects hold up today Geological processes of past are the same as Geological processes of past are the same as

todaytoday Stratigraphy serves to reconstruct history of Stratigraphy serves to reconstruct history of

the earththe earth Immense amount of time necessary for Immense amount of time necessary for

geological processes to effect change in the geological processes to effect change in the landscape landscape

Age of earth: The current estimate is 4.5 Age of earth: The current estimate is 4.5 billion yearsbillion years

Counterevidence to Lyell’s ModelCounterevidence to Lyell’s Model

Five global catastrophes are Five global catastrophes are known to have occurred.known to have occurred.

Example: collision of asteroid Example: collision of asteroid with earth 65 m.y.a. wiped out with earth 65 m.y.a. wiped out 75% of world’s marine species)75% of world’s marine species)

Mississippi Delta is less than Mississippi Delta is less than 100,000 years old—and has been 100,000 years old—and has been shrinking since 3400 BCEshrinking since 3400 BCE

Evolutionary Theories: Acquired Evolutionary Theories: Acquired CharacteristicsCharacteristics Jean-Baptiste de LamarckJean-Baptiste de Lamarck (1744-1829) (1744-1829) Traits acquired in organism’s lifetimeTraits acquired in organism’s lifetime Acquired CharacteristicsAcquired Characteristics:: Are passed down to offspringAre passed down to offspring Product of Product of adaptationadaptation to changing environment to changing environment Progress from simple to complex organismsProgress from simple to complex organisms Example: elongation of giraffes’ necks to get at Example: elongation of giraffes’ necks to get at

leaves of taller treesleaves of taller trees Shortcoming:Shortcoming: No example to support theory; natural selection No example to support theory; natural selection

coupled with mutation better explain the coupled with mutation better explain the lengthening of giraffes’ neckslengthening of giraffes’ necks

Counterexamples abound; for example, Counterexamples abound; for example, generations of docking sheep's’ tails in rural generations of docking sheep's’ tails in rural Spain did not eliminate them. Spain did not eliminate them.

Evolutionary Theories: Natural Evolutionary Theories: Natural SelectionSelection

Natural selection Defined:Natural selection Defined: Evolutionary change byEvolutionary change by Differential reproductive Differential reproductive

success of individualssuccess of individuals within a within a species species (group of (group of

organism able to reproduce organism able to reproduce fertile offspring)fertile offspring)

Through successful Through successful adaptation to an environmentadaptation to an environment

Charles Darwin Charles Darwin (1809-1882) (1809-1882) Origin of Origin of SpeciesSpecies

Charles Darwin (above) observed that pigeons, Charles Darwin (above) observed that pigeons, dogs, and horses were subjected to artificial dogs, and horses were subjected to artificial selection in order to improve their breedingselection in order to improve their breeding

On Galapagos Islands in 1832, Darwin observed On Galapagos Islands in 1832, Darwin observed that 14 species of finches adapted in different that 14 species of finches adapted in different niches descented from a common ancestor (next niches descented from a common ancestor (next slide)slide)

He conceived the idea of natural selection and He conceived the idea of natural selection and after years of dithering finally published his after years of dithering finally published his conclusions in conclusions in The Origin of Species The Origin of Species in 1859in 1859

Alfred Russel WallaceAlfred Russel Wallace (below) drew the same (below) drew the same conclusions—but Darwin published the results conclusions—but Darwin published the results firstfirst

(Wallace made a bad career move: he sent his (Wallace made a bad career move: he sent his results to Darwin asking for comments. Oops!)results to Darwin asking for comments. Oops!)

Charles Darwin and Natural Charles Darwin and Natural SelectionSelection

Natural Selection: Definition and Natural Selection: Definition and ImplicationsImplications

Variations are already present when selection occursVariations are already present when selection occurs Natural selection has no particular direction—Natural selection has no particular direction—

change is randomchange is random Therefore, not all evolution is from the simple to the Therefore, not all evolution is from the simple to the

complexcomplex Species can and do become extinctSpecies can and do become extinct New species can and do arise (Darwin had no way New species can and do arise (Darwin had no way

of explaining how the originated, however.) of explaining how the originated, however.) Reproductive isolation makes for new speciesReproductive isolation makes for new species New species fill new niches, as the finches showedNew species fill new niches, as the finches showed Thus, dark-winged moths filled a new environment Thus, dark-winged moths filled a new environment

in a soot-darkened coal-fired steel city; birds did not in a soot-darkened coal-fired steel city; birds did not pick them offpick them off

The dark colored pepper moth is to the lower part of The dark colored pepper moth is to the lower part of the photothe photo

Evolutionary Theories: GeneticsEvolutionary Theories: Genetics

It was up to the Austrian monk Gregor Mendel It was up to the Austrian monk Gregor Mendel to discover the principle that would lead to the to discover the principle that would lead to the explanation how species originated.explanation how species originated.

He experimented with peas in monastery He experimented with peas in monastery gardengarden

In so doing, he found that smooth and wrinkled In so doing, he found that smooth and wrinkled peas when combined produced offspring peas when combined produced offspring resembling their parentsresembling their parents

Nothing but smooth peas appeared in Nothing but smooth peas appeared in generation 2generation 2

A ratio of 3 smooth peas to one wrinkled pea A ratio of 3 smooth peas to one wrinkled pea appeared in generation 3appeared in generation 3

The experiments provided the hereditary The experiments provided the hereditary foundation for “origin” of species: mutation or foundation for “origin” of species: mutation or genetic changegenetic change

Gregor Mendel and GeneticsGregor Mendel and Genetics Mendel experimented with six Mendel experimented with six

other traits: color of peas, other traits: color of peas, texture of pea pods, color of texture of pea pods, color of flowersflowers

He found the same outcomes He found the same outcomes over three generationsover three generations

The traits were each The traits were each determined by variants determined by variants (alleles) of a pair of genes.(alleles) of a pair of genes.

Mendelian traits were thereby Mendelian traits were thereby discovereddiscovered

Later, it would be discovered Later, it would be discovered that multiple genes could that multiple genes could determine a single trait, such determine a single trait, such as eye and skin coloras eye and skin color

Molecular GeneticsMolecular Genetics

The final step to understanding The final step to understanding origins of species came with the origins of species came with the discovery by James Watson (left) discovery by James Watson (left) and Francis Crick (right) of a and Francis Crick (right) of a double helix molecule that double helix molecule that determine traits of all species determine traits of all species

Called DNA, they found that Called DNA, they found that mutations could change the traits mutations could change the traits of a species—any species of a of a species—any species of a plant or animal.plant or animal.

Details of this process are Details of this process are discussed in the next set of slides. discussed in the next set of slides.

ConclusionConclusion

Trends in history of evolutionary thought have Trends in history of evolutionary thought have been reviewedbeen reviewed

Creationism to evolutionary models of changeCreationism to evolutionary models of change Catastrophism to uniformitarianismCatastrophism to uniformitarianism Essentialism to natural selectionEssentialism to natural selection Chain of being to variation by random mutationChain of being to variation by random mutation Evidence fits evolutionary change better than model Evidence fits evolutionary change better than model

of creationof creation How evolutionary change occurs is covered in the How evolutionary change occurs is covered in the

next sets of slides.next sets of slides.