Darwin’s Theory of Evolution
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Transcript of Darwin’s Theory of Evolution
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Darwin’s Theory of Evolution
Ch. 15 - 16
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Evolutionary Theory
• Collection of scientific facts, observations, and hypotheses
• Evolution – change over time• Theory – well-supported testable explanation of
phenomena that have occurred
• I AM TEACHING YOU ABOUT A THEORY, JUST LIKE THE BIG BANG THEORY, OR HAVING A THEORY AS TO WHY SOME OF YOU LIKE PIZZA.
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Darwin
• 1831 – Darwin joined the Beagle and set sail around the world
• He was interested in nature and organisms• He collected evidence, samples, notes,
observations, etc.• He put this evidence together to come up with
his theory of evolution.
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Darwin and the Galapagos Islands
• Darwin traveled to the islands• He noticed that each island had its own
climate – some dry, some rainy, some humid, etc.
• The plants and animals on each island were different
• Each island had its own “version” of a tortoise, but they were different on each island… why?
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Darwin’s Observations
• Variation – he noticed that all species had variations of them– Tortoises – different shells– Finches – different beaks
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Darwin’s Conclusion
• Natural selection – “survival of the fittest”• All organisms struggle to survive – compete
for food, mates,, space, etc.• Any adaptation that increases the chance of
survival will stick around– Speed, camouflage, protection, etc.
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Natural Selection
• Example – mole rats• Some have big claws for digging, some have
sharp claws for climbing, and some have no claws
• All the mole rats live together with a predator• The predator has good sight and smell, can
climb, but can’t dig• Which mole rats are more likely to survive?
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Darwin’s Finches
• The Galapagos islands also have varieties of finches
• Each subspecies of finch has a different beak
• Each subspecies of finch has a different diet
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Natural Selection
• Those organisms with favorable traits will survive and pass on their characteristics to their offspring
• Another example:– 3 types of spiders
• Big – easily seen by predators• Small – can’t find food• Medium - survive
– after many generations which size spider is likely to be around?
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Natural Selection• Survival of the biggest?
– NO!• Survival of the fastest?
– NO!• Survival of the lightest?
– NO!• Survival of the fittest?
– YES!
• What does that mean?– Best adapted for their situation
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Current Evidence for Evolution
• 4 pieces of evidence currently support evolution– Fossils– Geographic distribution– Homologous body structures– Similarities in embryology
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Fossil Evidence
• Fossil – remains of ancient life• Fossils are found in layers• Older layers contain organisms that are not
found in younger layers• This indicates they were present but did not
survive
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Geographic Distribution Evidence
• There are organisms living on different continents with similar traits
• Example – p. 383– Each organism has very similar characteristics that
helps it adapt to its environment, which are also similar
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Homologous Body Structure Evidence
• Structures that have different mature forms, but the same embryonic tissues
• This supports that all 4-limbed organisms evolved from a common ancestor
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Embryology Evidence
• Supports homologous structures
• Many organisms with backbones look very similar during early embryonic development
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Summary of Darwin’s Theory
• All species have variation• These variations are either favorable or not• The favorable variations help organisms
survive – those traits will stick around• Unfavorable variations do not help organisms
survive – those traits will eventually disappear• Organisms with similar traits evolved from a
common ancestor