1 Chapter 15 Darwin's Theory of Evolution. 2 15–1 The Puzzle of Life's Diversity This variety of living things is called biological diversity. This variety.

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Chapter 15 Chapter 15 Darwin's Theory of Evolution Darwin's Theory of Evolution

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15–1 The Puzzle of Life's Diversity 15–1 The Puzzle of Life's Diversity

This variety of living things is called biological This variety of living things is called biological diversity. diversity.

How did all these different organisms arise? How did all these different organisms arise? How are they related? How are they related?

EvolutionEvolution, or change over time, is the process by , or change over time, is the process by which modern organisms have descended from which modern organisms have descended from ancient organisms. ancient organisms.

A scientific A scientific theorytheory is a well-supported testable is a well-supported testable explanation of phenomena that have occurred in explanation of phenomena that have occurred in the natural world. the natural world.

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Voyage of the Voyage of the BeagleBeagle Charles Darwin (born February 12, 1809 in Charles Darwin (born February 12, 1809 in

England)England) 1831 – set sail on the H.M.S. 1831 – set sail on the H.M.S. BeagleBeagle

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During his travels, Darwin made numerous During his travels, Darwin made numerous observations and collected evidence that observations and collected evidence that led him to propose a revolutionary led him to propose a revolutionary hypothesis about the way life changes over hypothesis about the way life changes over time. time.

That hypothesis, now supported by a huge That hypothesis, now supported by a huge body of evidence, has become the theory body of evidence, has become the theory of of evolutionevolution. .

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On The VoyageOn The Voyage

Collected plants & animals on landCollected plants & animals on land At sea – studied specimens, read, At sea – studied specimens, read,

recorded observationsrecorded observations Saw great diversity in the organisms – Saw great diversity in the organisms –

enormous numbers of species!enormous numbers of species!

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Patterns of Diversity Patterns of Diversity Plants and animals seemed so Plants and animals seemed so

well suited to their well suited to their environmentsenvironments

Impressed by the many ways Impressed by the many ways organisms survive and organisms survive and reproducereproduce

Similar areas on different Similar areas on different continents were inhabited by continents were inhabited by very different animals.very different animals. Ex: why are there no rabbits on Ex: why are there no rabbits on

the Australian grasslands? No the Australian grasslands? No kangaroos in England?kangaroos in England?

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Living Organisms and Fossils Living Organisms and Fossils

Darwin also collected fossilsDarwin also collected fossils Some fossils looked like organisms that were Some fossils looked like organisms that were

still alivestill alive Other fossils looked completely different!Other fossils looked completely different! Darwin wondered:Darwin wondered:

Why had so many of these species disappeared?Why had so many of these species disappeared? How were they related to living species? How were they related to living species?

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The Galápagos Islands The Galápagos Islands 1000 km west of South America (Ecuador)1000 km west of South America (Ecuador) Islands are close together but very different Islands are close together but very different

climatesclimates Darwin was fascinated in particular by the land Darwin was fascinated in particular by the land

tortoises and marine iguanas tortoises and marine iguanas

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The shape of a tortoise's shell could be used to The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited. identify which island a particular tortoise inhabited.

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The Journey HomeThe Journey Home

Darwin began to wonder if animals living on Darwin began to wonder if animals living on different islands had once been members of different islands had once been members of the same species. the same species.

these separate species would have evolved these separate species would have evolved from an original South American ancestor from an original South American ancestor species after becoming isolated from one species after becoming isolated from one another another

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Geological InformationGeological Information Massive, rich fossil record – much older than Massive, rich fossil record – much older than

the current age of the earth beliefs.the current age of the earth beliefs. James Hutton (1795) – old earth – great earth James Hutton (1795) – old earth – great earth

changes take timechanges take time Charles Lyell (1831) – the processes shaping Charles Lyell (1831) – the processes shaping

the Earth now are the same ones that shaped the Earth now are the same ones that shaped the earth in the pastthe earth in the past Could life change as earth has changed?Could life change as earth has changed?

15-2 Ideas that shaped 15-2 Ideas that shaped Darwin’s thinkingDarwin’s thinking

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Jean Baptiste LamarckJean Baptiste Lamarck 18091809 ““living things have changed over time”living things have changed over time” Species descended from other speciesSpecies descended from other species Lamarck’s theory of evolution:Lamarck’s theory of evolution:

Tendency toward perfectionTendency toward perfection Use and DisuseUse and Disuse Inheritance of Acquired TraitsInheritance of Acquired Traits

Why was he wrong?Why was he wrong? Behavior doesn’t affect the DNABehavior doesn’t affect the DNA

He was WRONG.He was WRONG.

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Thomas MalthusThomas Malthus

17981798 Population growth (if gone unchecked) would Population growth (if gone unchecked) would

quickly over run the earthquickly over run the earth Why don’t maple trees cover the earth since Why don’t maple trees cover the earth since

they each release 1000s of seeds?they each release 1000s of seeds? Darwin’s questions:Darwin’s questions:

What causes the deaths of so many?What causes the deaths of so many? What factors determine which survive and What factors determine which survive and

reproduce?reproduce?

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All species tend to produce more All species tend to produce more offspring than they can supportoffspring than they can support

Frog eggs

Turtle eggs

Insect eggs

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15-3 Darwin presents his case15-3 Darwin presents his case

Worked for years but scared to publish Worked for years but scared to publish because of religious backlashbecause of religious backlash

1858 – sent an essay by Alfred Russell 1858 – sent an essay by Alfred Russell Wallace summarizing Darwin’s theory of Wallace summarizing Darwin’s theory of evolutionevolution

1859 – Darwin publishes “On the origin of 1859 – Darwin publishes “On the origin of species by means of natural selection”species by means of natural selection”

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What did Darwin say?What did Darwin say?

Inherited Variation & Artificial SelectionInherited Variation & Artificial Selection Members of a species varyMembers of a species vary

Artificial Selection = nature provides the Artificial Selection = nature provides the variation and humans select the variations they variation and humans select the variations they find usefulfind useful Examples: fat hog, fast horse, high milk producing Examples: fat hog, fast horse, high milk producing

cowcow Does something in nature select the same way?Does something in nature select the same way?

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Variation within a speciesVariation within a species

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Artificial SelectionArtificial Selection

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Evolution by Natural SelectionEvolution by Natural Selection

Compared nature to artificial selectionCompared nature to artificial selection

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Struggle for ExistenceStruggle for Existence

Members of each species compete for food, Members of each species compete for food, space, mates, and other necessities of lifespace, mates, and other necessities of life

Predators (that are better/faster) catch more Predators (that are better/faster) catch more preyprey

Prey (faster, better camouflage) avoid being Prey (faster, better camouflage) avoid being caughtcaught Examples: fast cheetah, small rabbit, stronger lion, Examples: fast cheetah, small rabbit, stronger lion,

more colorful butterflymore colorful butterfly

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Preying Mantis sunflower

Producing more offspring than can possibly Producing more offspring than can possibly survive thus creating a struggle for existing survive thus creating a struggle for existing

resourcesresources

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Survival of the FittestSurvival of the Fittest

Fitness = being able to survive and reproduce Fitness = being able to survive and reproduce in its specific environmentin its specific environment

Fitness results from adaptationsFitness results from adaptations Adaptations = inherited characteristics that Adaptations = inherited characteristics that

improve an organisms chance of survivalimprove an organisms chance of survival Successful adaptation Successful adaptation better suited to the better suited to the

environment environment more fitness more fitness

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Adaptations –Adaptations – Anatomical/structural (quills on a porcupine)Anatomical/structural (quills on a porcupine) Physiological (photosynthesis)Physiological (photosynthesis) Behavioral (live/hunt in groups)Behavioral (live/hunt in groups)

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Low Fitness Low Fitness organisms die off organisms die off High Fitness High Fitness survive + reproduce survive + reproduce

Survival of the Fittest! Survival of the Fittest!

Natural Selection of most fit organisms!Natural Selection of most fit organisms!

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Nature (the environment) will Nature (the environment) will determine which organism is the determine which organism is the

fittest to Survivefittest to Survive

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Natural SelectionNatural Selection

Results from NO human intervention, control, Results from NO human intervention, control, or directionor direction

Results in changes in the inherited Results in changes in the inherited characteristics of a characteristics of a populationpopulation

Increases a species’ fitness in the environment Increases a species’ fitness in the environment (over time!)(over time!)

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Descent with ModificationDescent with Modification

Over large amounts of time… natural selection Over large amounts of time… natural selection produces organisms: produces organisms: with different structureswith different structures establishes different nichesestablishes different niches occupies different habitatsoccupies different habitats

organisms look different than their ancestorsorganisms look different than their ancestors Descent with modification = each living thing Descent with modification = each living thing

has descended with changes, from other has descended with changes, from other species over time.species over time.

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Common AncestorsCommon Ancestors Implies that organisms are all related to one Implies that organisms are all related to one

another.another. Tiger, panther, cheetah – relatedTiger, panther, cheetah – related Horses, dogs, cats – related farther backHorses, dogs, cats – related farther back Mammals, birds, reptiles, fish – related even farther Mammals, birds, reptiles, fish – related even farther

backback All living things – related!All living things – related!

Single Tree of Life!Single Tree of Life!

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Evidence of EvolutionEvidence of Evolution

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Living things have been evolving on Living things have been evolving on Earth for millions of years…Earth for millions of years…

Evidence..Evidence.. Fossil RecordFossil Record Geographic distribution of living speciesGeographic distribution of living species Homologous body structuresHomologous body structures

body part with the same basic structure and embryonic body part with the same basic structure and embryonic origin as that of another organism, though not necessarily origin as that of another organism, though not necessarily sharing the same function sharing the same function

Similarities in early development Similarities in early development (embryology)(embryology)

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The Fossil RecordThe Fossil Record

Fossils = remains of ancient lifeFossils = remains of ancient life Different layers of rock were formed at Different layers of rock were formed at

different times during Earth’s history.different times during Earth’s history. Darwin proposed that organisms had Darwin proposed that organisms had

coming into being, lived, and vanished.coming into being, lived, and vanished. Life had changed over time!Life had changed over time!

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Fossil Cephalopods Fossil Cephalopods    

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Fossil record of the modern horseFossil record of the modern horse

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FossilFossilrecord record of the of the camelcamel

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Since Darwin…Since Darwin… The number of known fossils has gone up The number of known fossils has gone up

dramatically!dramatically! Researchers have discovered many hundreds of Researchers have discovered many hundreds of

transitional fossilstransitional fossils that document various that document various intermediate stages in the evolution of modern intermediate stages in the evolution of modern species from organisms that are now extinct. species from organisms that are now extinct.

Gaps remain in the fossil records Gaps remain in the fossil records These gaps do not indicate weakness in the These gaps do not indicate weakness in the

theory of evolution itself. Rather, they point out theory of evolution itself. Rather, they point out uncertainties in our understanding of exactly uncertainties in our understanding of exactly how some species evolved. how some species evolved.

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Geographic Distribution of Living Geographic Distribution of Living Species  Species 

Darwin wondered about the finches he found in Darwin wondered about the finches he found in the Galapagos Islands.the Galapagos Islands.

Where were they similar but still different?Where were they similar but still different? Also.. Slightly different from S. American mainland Also.. Slightly different from S. American mainland

speciesspecies Could the birds have changed as they adapted to Could the birds have changed as they adapted to

local environments?local environments?

=> descended with modification from a common => descended with modification from a common mainland ancestor mainland ancestor

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Convergent EvolutionConvergent Evolution

Darwin found entirely different species of Darwin found entirely different species of animals on the continents of South America and animals on the continents of South America and Australia. Australia.

Similar environments on those continents Similar environments on those continents he he sometimes saw different animals that had sometimes saw different animals that had similar anatomies and behaviors. similar anatomies and behaviors.

The existence of similar but unrelated species The existence of similar but unrelated species was a puzzle to Darwin. was a puzzle to Darwin.

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Similar Species in Similar Species in Similar EnvironmentsSimilar Environments

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Convergent EvolutionConvergent Evolution

The adaptive The adaptive evolution of evolution of superficially similar superficially similar structures, such as structures, such as the wings of birds the wings of birds and insects, in and insects, in unrelated species unrelated species subjected to similar subjected to similar environments. environments.

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Unrelated organisms come Unrelated organisms come to resemble one another to resemble one another

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Analogous StructuresAnalogous Structures

Structures that serve the same function in different Structures that serve the same function in different species but they evolved independently species but they evolved independently

same function, different structuresame function, different structure Ex: bat wing, butterfly wingEx: bat wing, butterfly wing

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Divergent EvolutionDivergent Evolution

two or more related species becoming more two or more related species becoming more and more dissimilarand more dissimilar

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Homologous Body Structures Homologous Body Structures 

striking anatomical similarities among the body striking anatomical similarities among the body parts of animals with backbones parts of animals with backbones

of reptiles, birds, and mammals—arms, wings, of reptiles, birds, and mammals—arms, wings, legs, and flippers—vary greatly in form and legs, and flippers—vary greatly in form and function. function.

all constructed from the same basic bonesall constructed from the same basic bones limbs has adapted in ways that enable limbs has adapted in ways that enable

organisms to survive in different environments organisms to survive in different environments

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Homologous Body Structures Homologous Body Structures 

structures that structures that have different have different mature forms in mature forms in different different organisms but organisms but develop from the develop from the same embryonic same embryonic tissuestissues

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Vestigial Organs Vestigial Organs organ that serves no useful function in an organ that serves no useful function in an

organismorganism Why would an organism possess organs with Why would an organism possess organs with

little or no function? little or no function? One possibility = presence of a vestigial organ may One possibility = presence of a vestigial organ may

not affect an organism's ability to survive and not affect an organism's ability to survive and reproduce reproduce natural selection would not cause the natural selection would not cause the elimination of that organ. elimination of that organ.

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The human appendix

has no function in

humans but is very

important in cows and

other animals

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Human tailbone is a vestigial Human tailbone is a vestigial vertebrate tailvertebrate tail

Human tail bone consists of fused vertebrae that nolonger functionas a tail

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Similarities in Embryology  Similarities in Embryology 

embryos of many animals with backbones are embryos of many animals with backbones are very similarvery similar

many embryos look especially similar during many embryos look especially similar during early stages of development early stages of development

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chickens, turtles, and rats chickens, turtles, and rats

Pharyngeal slits

Dolphin

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Summary of Darwin's TheorySummary of Darwin's Theory

Individual organisms differ, and some of this Individual organisms differ, and some of this variationvariation is heritable. is heritable.

Organisms Organisms produce more offspringproduce more offspring than can than can survive, and many that do survive do not survive, and many that do survive do not reproduce.reproduce.

Because more organisms are produced than Because more organisms are produced than can survive, they can survive, they compete for limited compete for limited resourcesresources..

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Each unique organism has different advantages and Each unique organism has different advantages and disadvantages in the disadvantages in the struggle for existencestruggle for existence. . Individuals best suited to their environment survive Individuals best suited to their environment survive and reproduce most successfully. These organisms and reproduce most successfully. These organisms pass their heritable traits to their offspring. Other pass their heritable traits to their offspring. Other individuals die or leave fewer offspring. This process individuals die or leave fewer offspring. This process of of natural selectionnatural selection causes species to change over causes species to change over time.time.

Species alive today are Species alive today are descended with modificationdescended with modification from ancestral species that lived in the distant past. from ancestral species that lived in the distant past. This process, by which diverse species evolved from This process, by which diverse species evolved from common ancestors, unites all organisms on Earth into common ancestors, unites all organisms on Earth into a single tree of life.a single tree of life.