Early Ideas about Evolution and Darwin’s Observations SECTIONS 10.1 & 10.2.
Darwin’s Observations The Theory of Evolution by Natural Selection.
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Transcript of Darwin’s Observations The Theory of Evolution by Natural Selection.
Darwin’s Observations
The Theory of Evolution by Natural Selection
The HMS Beagle
• Charles Darwin embarked on the second voyage of the HMS Beagle on December 27,1831, on a survey expedition under the command of Captain Robert Fitzroy.
• The main purpose of the expedition was to map out the southern coast of South America, and Darwin was on board as a geologist, to collect specimens.
The HMS Beagle (cont’d)
• The journey was supposed to last 2 years, but the ship returned to England on October 2, 1836, almost 5 years after its departure.
What Darwin Saw
• Similar flora & fauna (plants & animals) on the Galapagos as on mainland South America
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What Darwin Saw (cont’d)
• Many species of finches and mockingbirds
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Other observations…
• The fossil record: – Glyptodon (like the armadillo)– Megatherium (like the sloth)
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Other observations (cont’d)
• Comparative anatomy of animals:– Homologous features:
Other observations (cont’d)
• Comparative anatomy of animals:– Analogous features:
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Other observations (cont’d)
• Comparative anatomy of animals:– Vestigial features:
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Other observations (cont’d)
• Investigated mechanisms of artificial selection (pigeon breeding, etc.)
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Other observations (cont’d)
• Thomas Malthus, Essay on the Principle of Population (1798)
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The Theory of Evolution by Natural Selection
• Observation 1: Individuals within a species vary in many ways.
• Observation 2: Some of this variability can be inherited.
• Observation 3: Every generation produces far more offspring that can survive and pass on their variations.
• Observation 4: Populations of species tend to remain stable in size.
The Theory of Evolution by Natural Selection
• Inference 1: Members of the same species compete with each other for survival.
• Inference 2: Individuals with more favourable variations are more likely to survive and pass them on. Survival is not random.
• Inference 3: As these individuals contribute proportionally more offspring to succeeding generations, the favourable variations will become more common. (This is natural selection.)