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Evolution by Natural Selection
Darwin: a reluctant rebel
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TINTORETTO The Creation of the Animals 1550
DOCTRINE TINTORETTO The Creation of the Animals 1550
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But the Fossil record… OBSERVATION
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Life’s Natural History is a record of Successions & Extinctions
mya Quaternary Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian Ediacaran Precambrian, Proterozoic, & Archarozoic 1.5 Plants 63 Birds Mammals 135 Reptiles Seed Plants Flowering Amphibians Insects 180 Dinosaurs Teleost Fish Land Plants 225 Jawless Fish Molluscs Arthropods Chordates Multicellular Animals 280 Green Algae Photosynthetic Bacteria 350 Anaerobic Bacteria 400 430 500 570 700 4500 Life’s Natural History is a record of Successions & Extinctions
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Life has changed over time & in turn has changed the Earth
Living creatures have changed Earth’s environment, making other life possible
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Evolution as Change Over Time
idea accepted before Darwin Evolution! Evolution! Evolution!
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LaMarck Organisms adapted to their environments by acquiring traits
change in their life time Disuse organisms lost parts because they did not use them — like the missing eyes & digestive system of the tapeworm Perfection with Use & Need the constant use of an organ leads that organ to increase in size — like the muscles of a blacksmith or the large ears of a night-flying bat transmit acquired characteristics to next generation Lamarck noted how well-adapted organisms were to their environments, and believed that fossils could be understood as less perfect forms which had perished in the struggle for increasing perfection. He explained adaptation as a result of change caused by environmental pressures.
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Charles Darwin 1809-1882 British naturalist
Proposed the idea of evolution by natural selection Collected clear evidence to support his ideas What did Darwin say? What evidence supports Evolution by Natural Selection? What impact did Evolution have on biology?
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Voyage of the HMS Beagle
Invited to travel around the world (22 years old!) makes many observations of nature main mission of the Beagle was to chart South American coastline After graduation Darwin was recommended to be the conversation companion to Captain Robert FitzRoy, preparing the survey ship Beagle for a voyage around the world. FitzRoy chose Darwin because of his education, his similar social class, and similar age as the captain. Darwin noted that the plants and animals of South America were very distinct from those of Europe Robert Fitzroy
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Voyage of the HMS Beagle
Stopped in Galapagos Islands 500 miles off coast of Ecuador The origin of the fauna of the Galapagos, 900 km west of the South American coast, especially puzzled Darwin. On further study after his voyage, Darwin noted that while most of the animal species on the Galapagos lived nowhere else, they resembled species living on the South American mainland. It seemed that the islands had been colonized by plants and animals from the mainland that had then diversified on the different islands
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Galapagos Recent volcanic origin most of animal species on the Galápagos live nowhere else in world, but they resemble species living on South American mainland. 500 miles west of mainland
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Succession of types Armadillos are native to the Americas, with most species found in South America. Glyptodont fossils are also unique to South America. Why should extinct armadillo-like species & living armadillos be found on the same continent?
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Mylodon (left) Giant ground sloth (extinct)
Modern sloth (right) “This wonderful relationship in the same continent between the dead and the living will…throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other class of facts.”
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Unique species Show Campbell videos!!!
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Darwin found… birds Finch? Sparrow? Woodpecker? Warbler? Collected many different birds on the Galapagos Islands. Thought he found very different kinds… Finch? Sparrow? Woodpecker? Warbler?
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But Darwin found… a lot of finches
Darwin was amazed to find out: All 14 species of birds were finches… But there is only one species of finch on the mainland! Large Ground Finch Finch? Sparrow? Woodpecker? Warbler? Small Ground Finch Finch? Sparrow? How did one species of finches become so many different species now? Warbler Finch Veg. Tree Finch Woodpecker? Warbler?
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Tree Thinking Descendant species Ancestral species Large-seed eater?
Large Ground Finch Small-seed eater? Small Ground Finch Darwin noted that the plants and animals of South America were very distinct from those of Europe. Organisms from temperate regions of South America were more similar to those from the tropics of South America than to those from temperate regions of Europe. Further, South American fossils more closely resembled modern species from that continent than those from Europe. Warbler? Warbler Finch Leaf-browser? Veg. Tree Finch
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Correlation of species to food source
Seed eaters Flower eaters Insect eaters Rapid speciation: new species filling new niches, because they inherited successful adaptations. Adaptive radiation
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Darwin’s finches Differences in beaks
associated with eating different foods survival & reproduction of beneficial adaptations to foods available on islands Warbler finch Cactus finch Woodpecker finch Sharp-beaked finch Small insectivorous tree finch Small ground finch Warbler finch Large insectivorous tree finch Cactus eater Tree finches Medium ground finch Ground finches Insect eaters Seed eaters Vegetarian tree finch Large ground finch Bud eater
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Darwin’s finches Darwin’s conclusions
small populations of original South American finches landed on islands variation in beaks enabled individuals to gather food successfully in the different environments over many generations, the populations of finches changed anatomically & behaviorally accumulation of advantageous traits in population emergence of different species
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Seeing this gradation & diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species has been taken & modified for different ends.
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Darwin’s finches Differences in beaks allowed some finches to…
successfully compete successfully feed successfully reproduce pass successful traits onto their offspring
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Correlation of species to food source
More observations… Correlation of species to food source Whoa, Turtles, too!
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Many islands also show distinct local variations in tortoise morphology…
…perhaps these are the first steps in the splitting of one species into several?
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