EVOLUTION

Charles Darwin

Darwin’s Theory of Evolution Evolution, or change over time, is the process by which modern organisms have descended from ancient organisms. Evolution, or change over time, is the process by which modern organisms have descended from ancient organisms. Evolution

How do you think Darwin came up with his theory?

Voyage of the Beagle

Patterns of Diversity Darwin visited Argentina and Australia which had similar grassland ecosystems.  But those grasslands were inhabited by very different animals and different from grasslands in England.

Patterns of Diversity Darwin posed challenging questions.  Why were there no rabbits in Australia, despite the presence of habitats that seemed perfect for them?  Why were there no kangaroos or koalas in England?

Living Organisms and Fossils Darwin collected the fossil remains of ancient organisms. Darwin collected the fossil remains of ancient organisms. Some of those fossils resembled organisms that were still alive today. Some of those fossils resembled organisms that were still alive today.

present day Sloth Fossils Darwin asked: Why should extinct sloths & modern sloths be found on the same continent? (extinct) Giant ground sloth

Living Organisms and Fossils Some fossils looked completely unlike any creature he had ever seen. Some fossils looked completely unlike any creature he 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?  How were they related to living species?

Galapagos Recently 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 tortoises in the Galápagos. Darwin was fascinated in particular by the land tortoises in the Galápagos. Giant tortoises varied in predictable ways from one island to another. Giant tortoises varied in predictable ways from one island to another. The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited. The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited.

Unique animals Darwin studied

The Journey Home Darwin pondered why characteristics of many plants and animals vary greatly among the islands Darwin pondered why characteristics of many plants and animals vary greatly among the islands Hypothesis: Separate species may have arisen from an original ancestor Hypothesis: Separate species may have arisen from an original ancestor

Ideas that shaped Darwin’s Thinking James Hutton: 1795 Theory of Geological change  Forces change earth’s surface shape  Changes are slow  Earth much older than thousands of years

Ideas that Shaped Darwin’s Thinking Charles Lyell Book: Principles of Geography Geographical features can be built up or torn down Geographical features can be built up or torn down Darwin thought if earth changed over time, what about life? Darwin thought if earth changed over time, what about life?

Lamarck’s Theory of Evolution Inheritance of Acquired Traits

 creatures developed traits during their lifetime  give those traits to their offspring  not accepted as valid Earlier ideas on Evolution

Population Growth Thomas Malthus-19th century English economist If population grew: If population grew:  Insufficient living space  Food runs out  Many will die Darwin applied this theory to animals

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

It turned out to be 14 species of finches… Finch?Sparrow? Woodpecker? Warbler? Finch?Sparrow? Woodpecker? Warbler? Darwin found… a lot of birds Large ground finch Small ground finch Warbler finchTree finch But there is only one species of finch on the mainland! Darwin asked: If the Galapagos finches came from the mainland, why are they so different now?

Finch?Sparrow? Woodpecker? Warbler? The finches cinched it! Large ground finch Small ground finch Warbler finchTree finch Big seed eaterSmall seed eater Insect eaterLeaf & bud eater Darwin said: Ahaaaa! A flock of South American finches were stranded on the Galapagos… Darwin found: The differences between species of finches were associated with the different food they ate. different beaks are inherited variations serve as adaptations that 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 finch Large insectivorous tree finch Vegetarian tree finch Cactus finch Sharp-beaked finch Small ground finch Medium ground finch Large ground finch Insect eaters Bud eater Seed eaters Cactus eater Warbler finch Tree finches Ground finches variation natural selection for best survival & reproduction From 1 species to 14 species…

Summary of Darwin’s Theory Individuals in nature differ from one another (variation) Individuals in nature differ from one another (variation) Organisms in nature produce more offspring than can survive, so many do not survive and do not reproduce. Organisms in nature produce more offspring than can survive, so many do not survive and do not reproduce. Because more organisms are produced than can survive, each species must struggle for resources Because more organisms are produced than can survive, each species must struggle for resources

Summary (cont.) Individuals best suited for the environment survive and reproduce most successfully Individuals best suited for the environment survive and reproduce most successfully Species change over time Species change over timeRevolutionary?

Darwin’s controversial conclusions Species alive today descended with modification from species that lived in the past Species alive today descended with modification from species that lived in the past All organisms on earth are united into a single family tree of life by common descent All organisms on earth are united into a single family tree of life by common descent