1. Outline 15-2: Ideas that Shaped Darwin’s Thinking
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Outline 15-2: Ideas that Shaped Darwin’s Thinking

2. I. An Ancient Changing Earth
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I. An Ancient Changing Earth
A. James Hutton
1. In 1795, he published a detailed hypothesis about the geological forces that had shaped the Earth.
2. Proposed that layers of Earth formed very slowly
3. Natural forces, such as wind, rain, heat & cold could shape the land into mountains & valleys over the course of millions of years.
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B. Charles Lyell
1. Wrote “Principles of Geology” which Darwin brought onto the Beagle
2. Said that scientists must explain past events in terms of processes they could actually observe.
a) Processes that shaped the Earth in the past should be the same as they are today.
b) Examples:
Volcanic eruptions change land
Erosion carves out canyons like the Grand Canyon
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4. Grand Canyon
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5. A. If Earth could change over time, why not living organisms?
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II. Influence on Darwin
A. If Earth could change over time, why not living organisms?
B. It would take many, many years for significant change to occur
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6. III. Jean Baptiste Lamarck (1809)
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III. Jean Baptiste Lamarck (1809)
1. Proposed a mechanism now called
the Inheritance of Acquired Characteristics.
a. Organisms may develop new traits during their lifetime (by use and disuse) because of a tendency towards perfection
b. Then the organisms pass these new traits on to their offspring
c. Over time, species change to become adapted to their environment
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7. Inheritance of Acquired Characteristics
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Large claw is passed onto its offspring
Male crab uses front claw repeatedly
Eventually all crabs have the large claw

8. a. He did not understand laws of inheritance
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2. Evaluating Lamarck’s Hypothesis
a. He did not understand laws of inheritance
b. An organism that changes during its lifetime is not likely to pass those changes on to their offspring.
c. Idea paved way for a mechanism concerning how species could change
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9. IV. Human Population Troubles
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IV. Human Population Troubles
A. Thomas Malthus
1. In 1798, he published a paper
2. Stated that babies were being born faster than adults were dying.
3. Eventually the human population would grow to the point where there was not enough space or food for everyone.
4. Only war, famine & disease kept the human population in check
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B. Influence on Darwin
1. This same principle should apply to organisms in nature
a) If all the offspring of a species survived they would eventually overrun the Earth.
2. Obviously this has not happened
a) Due to the fact that most offspring of wild animals & plants die before maturity.
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