Evolutionary Theory A Theory to Explain Change Over Time.
Transcript of Evolutionary Theory A Theory to Explain Change Over Time.
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Evolutionary TheoryEvolutionary Theory
A Theory to Explain Change Over TimeA Theory to Explain Change Over Time
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Modern Evolutionary TheoryModern Evolutionary Theory
• A theory is: a broad range of data that has been scientifically tested and supported.
• Modern evolutionary theory began when Charles Darwin presented evidence that evolution happens and offered an explanation of how it happens.
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Evolutionary Theory Keeps Changing Evolutionary Theory Keeps Changing & Expanding& Expanding
• Like most scientific theories, evolutionary theory keeps developing & expanding.
• Many scientists since Darwin have tested & added to his ideas.
Peter & Rosemary Grant-research Galapagos Finches
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Darwin’s Ideas From ExperienceDarwin’s Ideas From Experience
• In Darwin’s time, most people did not think that living things had changed over time.
• In fact, many doubted that Earth itself had ever changed.
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• But Darwin saw evidence of gradual change.
• Darwin’s experiences provided him with evidence of evolution at work.
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The Voyage of the BeagleThe Voyage of the Beagle
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Galapagos IslandsGalapagos Islands
• Darwin collected several different species of birds called finches.
• Each of the finches are very similar, but have different bills.
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• Each bill is suited to a particular food available on the individual islands.
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Galapagos Plants and AnimalsGalapagos Plants and Animals
• Darwin noticed that many of the islands’ plants and animals were similar but not identical to species in South America.
• He suggested they were descendants of S. American species with modifications.
Darwin’s original notes on descent with modification to explain the different species of birds, tortoises, etc. seen on the Galapagos.
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Descent with modification = EvolutionDescent with modification = Evolution
• Each of the Hawaiian honeycreeper species has a bill specialized for eating certain foods. Scientists suggest that all 23 honeycreeper species apparently arose from a single species that migrated to Hawaii.
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Years of ReflectionYears of Reflection• After returning from his
voyage, Darwin spent many years studying his data.
• He did not report his ideas for many years.
• He took time to gather more data and to form a strong explanation for how evolution happens.
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Breeding & SelectionBreeding & Selection• Darwin bred exotic pigeons
and studied the work of others who bred dogs, orchids, crops, and other livestock.
• Breeders take advantage
of natural variation in traits within a species.
• This is artificial selection.
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Artificial SelectionArtificial Selection – The human practice of – The human practice of breeding animals or plants that have certain breeding animals or plants that have certain
traits.traits.
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Natural SelectionNatural Selection
• Darwin suggested that nature “selects” which organisms survive and reproduce.
• Survival of the Fittest
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Darwin’s Ideas from OthersDarwin’s Ideas from Others
• In Darwin’s time, most people—including scientists—believed that each species was created once and stayed the same forever.
• But, this view could not explain fossils of organisms that no longer exist, such as dinosaurs.
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Do Organisms Change over Time?Do Organisms Change over Time?
• Some scientists tried to explain such observations by saying that species could die out but never change.
• Others proposed various mechanisms to explain how species may change over time.
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LamarckLamarck
• In 1809, the French scientist, Jean Baptiste Lamarck proposed an explanation for how organisms may change over generations.
• He noticed that organisms are usually well adapted to their environment.
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……LamarckLamarck
• Lamarck proposed (like Darwin) that organisms change over time as they adapt to changing environments.
• The mechanism for that change, however, that was proposed by Lamarck was wrong.
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• He proposed that changes due to use or disuse of a characteristic would be passed on to the offspring.
• Ex: building muscles would mean their baby would have bigger muscles.
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Use and DisuseUse and Disuse• Lamarck proposed a
reason why giraffes have a long neck:
• He said that giraffes stretched their necks to reach leaves high in the trees. Their offspring, therefore would have longer necks.
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The Theory of Evolution by The Theory of Evolution by Natural Selection Natural Selection (See page 381)(See page 381)
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Natural SelectionNatural Selection
• The process by which individuals that are better adapted to their environment survive & reproduce more successfully than less well adapted individuals do.
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4 Steps to Natural Selection4 Steps to Natural Selection
1. Overproduction – Every population is capable of producing more offspring than can possibly survive.
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2. Variation – Variations exist within every population. Much of this variation is in the form of inherited traits.
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3. Selection – In a given environment, having a particular trait can make individuals more likely to survive & have successful offspring than others.
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4. Adaptation – Over time, those traits that improve survival & reproduction will become more common in a population.
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Natural Selection AnimationNatural Selection Animation
• http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ev/m2/s1/evm2s1_6.htm