The Theory of EVOLUTION

Charles Darwin

Darwin’s Theory of Evolution

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

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

Voyage of the Beagle

Patterns of Diversity

Darwin visited Argentina and Australia which had Darwin visited Argentina and Australia which had similar grassland ecosystems. similar grassland ecosystems.

those grasslands were inhabited by very different those grasslands were inhabited by very different animals. animals.

neither Argentina nor Australia was home to the neither Argentina nor Australia was home to the sorts of animals that lived in European grasslands.sorts of animals that lived in European grasslands.

Patterns of Diversity

Darwin posed challenging questions. Darwin posed challenging questions. Why were there no rabbits in Australia, despite the Why were there no rabbits in Australia, despite the

presence of habitats that seemed perfect for them?presence of habitats that seemed perfect for them?

Why were there no kangaroos in England?Why were there no kangaroos in England?

Living Organisms and Fossils

Darwin collected the preserved remains of Darwin collected the preserved remains of ancient organisms, called ancient organisms, called fossils. .

Some of those fossils resembled organisms that Some of those fossils resembled organisms that were still alive today.were still alive today.

Living Organisms and Fossils   Others looked completely unlike any creature he had Others looked completely unlike any creature he had

ever seen. ever seen.

As Darwin studied fossils, new questions arose. As Darwin studied fossils, new questions arose. 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?

Fossils

The Galapagos Island The smallest, lowest islands were hot, The smallest, lowest islands were hot,

dry, and nearly barren-Hood Island-sparse dry, and nearly barren-Hood Island-sparse vegetationvegetation

The higher islands had greater rainfall and The higher islands had greater rainfall and a different assortment of plants and a different assortment of plants and animals-Isabela- Island had rich animals-Isabela- Island had rich vegetationvegetation..

The Galapagos Island

Darwin was fascinated in particular by the land Darwin was fascinated in particular by the land tortoises and marine iguanas in the Galápagos. tortoises and marine iguanas in the Galápagos.

Giant tortoises varied in predictable ways from Giant tortoises varied in predictable ways from one island to another.one island to another.

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 identify which island a particular tortoise inhabited. inhabited.

Animals found in the Galapagos

Land TortoisesLand Tortoises

Darwin FinchesDarwin Finches

Blue-Footed BoobyBlue-Footed Booby

Marine IguanasMarine Iguanas

Darwin Finches

The Journey Home

Darwin Observed that characteristics Darwin Observed that characteristics of many plants and animals vary of many plants and animals vary greatly among the islandsgreatly among the islands

Hypothesis:Hypothesis: Separate species may Separate species may have arose from an original ancestorhave arose from an original ancestor

Ideas that shaped Darwin’s Thinking James Hutton:James Hutton: 1795 Theory of 1795 Theory of

Geological changeGeological change Forces change Forces change

earth’s surface earth’s surface shapeshape

Changes are slowChanges are slow Earth much older Earth much older

than thousands of than thousands of yearsyears

Ideas that Shaped Darwin’s Thinking Charles LyellCharles Lyell Book: Book: Principles of Principles of

GeographyGeography Geographical features Geographical features

can be built up or torn can be built up or torn downdown

Darwin thought if Darwin thought if earth changed over earth changed over time, what about life?time, what about life?

Lamarck

Lamarck’s Theory of Evolution

Tendency toward Perfection(Giraffe Tendency toward Perfection(Giraffe necks)necks)

Use and Disuse (bird’s using forearms)Use and Disuse (bird’s using forearms)

Inheritance of Acquired TraitsInheritance of Acquired Traits

Population Growth Thomas MalthusThomas Malthus--

19th century English 19th century English economisteconomist

If population grew If population grew (more Babies born (more Babies born than die)than die) Insufficient living Insufficient living

spacespace Food runs outFood runs out Darwin applied this Darwin applied this

theory to animalstheory to animals

Publication of Orgin of Species

Russel Wallace wrote Russel Wallace wrote an essay summarizing an essay summarizing evolutionary change evolutionary change from his field work in from his field work in MalaysiaMalaysia

Gave Darwin the drive Gave Darwin the drive to publish his findingsto publish his findings

Natural Selection & Artificial Selection Genetic variationGenetic variation--differences among --differences among

individuals of a speciesindividuals of a species

Artificial selectionArtificial selection- nature provides the - nature provides the variation among different organisms, and variation among different organisms, and humans select those variations they find humans select those variations they find

usefuluseful..

Evolution by Natural Selection

The Struggle for ExistenceThe Struggle for Existence-members of -members of each species have to compete for food, each species have to compete for food, shelter, other life necessitiesshelter, other life necessities

Survival of the FittestSurvival of the Fittest-Some individuals -Some individuals better suited for the environmentbetter suited for the environment

Struggle For Existence & Survival of The Fittest

Natural Selection

Over time, natural Over time, natural selection results in selection results in changes in inherited changes in inherited characteristics of a characteristics of a population. These population. These changes increase a changes increase a species fitness in its species fitness in its environmentenvironment

Descent

Descent with ModificationDescent with Modification-Each living organism has -Each living organism has descended, with changes from other species over timedescended, with changes from other species over time

Common DescentCommon Descent- were derived from common ancestors- were derived from common ancestors

Evidence of Evolution

The Fossil RecordThe Fossil Record

Geographic Distribution of Living ThingsGeographic Distribution of Living Things

Homologous Body StructuresHomologous Body Structures

Similarities in Early DevelopmentSimilarities in Early Development

Evidence for Evolution

The Fossil RecordThe Fossil Record--Layers show changeLayers show change

Evidence of Evolution Geographic Geographic

Distribution of Distribution of Living Things-Living Things-similar similar environments have environments have similar types of similar types of organismsorganisms

Homologous Structures

Homologous StructuresHomologous Structures-structures that -structures that have different mature forms in different have different mature forms in different organisms, but develop from the same organisms, but develop from the same embryonic tissueembryonic tissue

Evidence for Evolution

Vestigial organsVestigial organs-organs that serve -organs that serve no useful function in an organismno useful function in an organism

i.e.) appendix, miniature legs, armsi.e.) appendix, miniature legs, arms

Similarities in Early Development

Summary of Darwin’s Theory

Individuals in nature differ from one Individuals in nature differ from one anotheranother

Organisms in nature produce more Organisms in nature produce more offspring than can survive, and many of offspring than can survive, and many of those who do not survive do not reproduce.those who do not survive do not reproduce.

Summary of Darwin’s Theory

Because more organisms are produced than Because more organisms are produced than can survive, each species must struggle for can survive, each species must struggle for resourcesresources

Each organism is unique, each has Each organism is unique, each has advantages and disadvantages in the advantages and disadvantages in the struggle for existencestruggle for existence

Summary (cont.)

Individuals best suited for the environment Individuals best suited for the environment survive and reproduce most successfulsurvive and reproduce most successful

Species change over timeSpecies change over time

Summary (cont.)

Species alive today descended with modification Species alive today descended with modification from species that lived in the pastfrom species that lived in the past

All organisms on earth are united into a single All organisms on earth are united into a single family tree of life by common descentfamily tree of life by common descent