EVOLUTION

Charles Darwin

Darwin’s Theory of Evolution

EvolutionEvolution, 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.

How do you think Darwin came up with his theory?

Voyage of the Beagle

Patterns of Diversity

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

But those grasslands were inhabited by very different But those grasslands were inhabited by very different animals and different from grasslands in England. animals and different from grasslands in England.

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

Living Organisms and Fossils

Darwin collected the fossil remains of ancient Darwin collected the fossil remains of ancient organisms. organisms.

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

present day Sloth

Fossils

Darwin asked:Darwin asked:

Why should Why should extinct sloths & extinct sloths & modern sloths be modern sloths be found on the same found on the same continent?continent?

(extinct) Giant ground sloth

Living Organisms and Fossils   Some fossils looked completely unlike any creature he Some fossils looked completely unlike any creature he

had ever seen. had 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?

GalapagosRecently formed volcanic islands. Most of animals on the Galápagos live nowhere else in world, but they look like species living on South American mainland.

800 km west of Ecuador

The Galapagos Islands

Darwin was fascinated in particular by the land Darwin was fascinated in particular by the land tortoises in the Galápagos. tortoises 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.

Unique animals Darwin studied

The Journey Home

Darwin pondered why characteristics Darwin pondered why 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 arisen from an original ancestorhave arisen from an original ancestor

Ideas that shaped Darwin’s ThinkingJames 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 ThinkingCharles LyellCharles LyellBook: 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’s Theory of Evolution

Inheritance of Inheritance of Acquired Acquired TraitsTraits

creatures developed creatures developed traits during their traits during their lifetime lifetime

give those traits to give those traits to their offspringtheir offspring

not accepted as validnot accepted as valid

Earlier ideas on Evolution

Population GrowthThomas MalthusThomas Malthus-19th -19th

century English century English economisteconomist

If population grew:If population grew: Insufficient living Insufficient living

spacespace Food runs outFood runs out Many will dieMany will die

Darwin applied this Darwin applied this theory to animalstheory to animals

Artificial Selection

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..

It turned out to be 14 species of It turned out to be 14 species of finches…finches…

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are needed to see this picture.

Finch? Sparrow?

Woodpecker? Warbler?

Finch? Sparrow?

Woodpecker? Warbler?

Darwin found… a lot of birds

Large ground finch

Small ground finch

Warbler finch Tree finch

ButBut there is only there is only oneone species species of finch on the mainland!of finch on the mainland!

Darwin asked:Darwin asked:

If the Galapagos If the Galapagos finches came from the finches came from the mainland, why are they mainland, why are they

so different now?so different now?

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are needed to see this picture.

Finch? Sparrow?

Woodpecker? Warbler?

The finches cinched it!

Large ground finch

Small ground finch

Warbler finch Tree finch

Big seed eater Small seed eater

Insect eater Leaf & bud eater

Darwin said:Darwin said:

Ahaaaa! Ahaaaa! A flock of South A flock of South

American finches American finches were stranded on the were stranded on the

Galapagos…Galapagos…

Darwin found: Darwin found: The differences between The differences between species of finches were species of finches were associated with the associated with the different food they ate.different food they ate.

different beaks are inherited variations

serve as adaptationsthat help birds compete for food

these birds survive & reproduce

pass on the genes for those more fit beaks

over time nature selected for different species with different beaks

Warbler finch

Woodpecker finch

Small insectivorous

tree finchLarge

insectivoroustree finch

Vegetariantree finch

Cactus finch

Sharp-beaked finch

Small groundfinch

Mediumground finch

Large groundfinch

Insect eaters

Bud eater

Seed eaters

Cactuseater

Warbler

finch

Tree

finc

hes Ground finches

variationnatural selection for best survival & reproduction

From 1 species to 14 species…

Summary of Darwin’s Theory

Individuals in nature differ from one another Individuals in nature differ from one another (variation)(variation)

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

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

Summary (cont.)

Individuals best suited for the environment Individuals best suited for the environment survive and reproduce most successfullysurvive and reproduce most successfully

Species change over timeSpecies change over time

Revolutionary?Revolutionary?

Darwin’s controversial conclusions

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