1. 15–2 Ideas That Shaped Darwin's Thinking
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2. An Ancient, Changing Earth
Darwin’s voyage came during one of the most exciting periods in the history of Western science.
Explorers were traveling the globe, and great thinkers were beginning to challenge established views about the natural world.
Some people found Darwin’s ideas too shocking to accept.
Most Europeans of the time believed that the Earth and all of its life forms had been created only a few _______ years before, and that since then neither the planet nor its living species had ____________.
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3. An Ancient, Changing Earth
Hutton and Geological Change
James Hutton and Charles Lyell helped scientists recognize that Earth is many_______of years old, and the processes that changed Earth in the past are the same processes that operate in the present.
In 1795, James Hutton published a hypothesis about the ________________ forces that shaped Earth.
Most of these geological forces operate very slowly, are shaped by a variety of_______forces such as rain, wind, heat, and cold, and occur over_______of years.
Hutton proposed that Earth had to be much more than a few thousand years old.
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4. An Ancient, Changing Earth
Lyell's Principles of Geology
Lyell stressed that scientists must explain past events in terms of processes that they can actually ________.
The processes that shaped the Earth millions of years earlier continue in the present.
Lyell’s work explained how geological features could be built up or torn down over long periods of time.
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5. An Ancient, Changing Earth
This understanding of geology influenced Darwin:
If the Earth could change over time,______might change as well.
It would have taken many years for life to change in the way Lyell suggested.
This would have been possible only if the Earth were extremely _________.
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6. Lamarck's Evolution Hypotheses
Jean-Baptiste Lamarck recognized that:
living things have changed over time.
all species were_____________from other species.
organisms were___________to their environments.
Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their_____________.
These traits could then be passed on to their offspring. Over time, this process led to change in a species.
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7. Lamarck's Evolution Hypotheses
Tendency Toward Perfection 
Lamarck proposed that all organisms have an innate tendency toward__________and perfection.
They are continually changing and acquiring features that help them live more successfully in their environments.
ie: birds gain urge to fly over many generations birds try to fly wings increased in size and flight became better
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8. Lamarck's Evolution Hypotheses
Use and Disuse
Lamarck proposed that organisms could _____the size or shape of particular organs by using their bodies in new ways.
ie: front limbs used for flying turned them into wings; disuse of wings causes them to decrease in size and eventually disappear
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9. Lamarck's Evolution Hypotheses
Lamarck's Hypothesis
A male fiddler crab uses its front claw to ward off predators and to attract mates.
Lamarck proposed that the selective use or disuse of an organ led to a change in that organ that was then passed on to offspring. This proposed mechanism is shown here applied to fiddler crabs. (1) The male crab uses its small front claw to attract mates and ward off predators. (2) Because the front claw has been used repeatedly, it becomes larger.
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10. Lamarck's Evolution Hypotheses
Lamarck's Hypothesis
Because the front claw is used repeatedly, it becomes larger.
This characteristic (large claw) is passed onto its offspring.
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11. Lamarck's Evolution Hypotheses
Inheritance of Acquired Traits
Lamarck thought that acquired characteristics could be______________.
He believed that if an animal acquired a particular feature in its lifetime, that feature would be passed on to its offspring.
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12. Lamarck's Evolution Hypotheses
Evaluating Lamarck's Hypotheses
Lamarck’s hypotheses of evolution are_________in several ways.
Lamarck did not know:
how traits are_____________.
that an organism’s________has no effect on its heritable characteristics.
However, he paved the way for the work of later biologists by being one of the first to suggest that organisms are adapted to their environments.
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Population Growth
Population Growth
In 1798, Thomas Malthus published a book in which he noted that babies were being born faster than people were dying.
Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.
The only forces he observed that worked against this growth were ________________________________.
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Population Growth
When Darwin read Malthus’s work, he realized that this reasoning applied even more strongly to plants and animals because humans produce far ________ offspring than most other species do.
If all the offspring of almost any species survived for several generations, they would overrun the world.
The overwhelming majority of a species’ offspring die, and of those that survive, few succeed in ____________________.
This information was central to Darwin’s explanation of evolutionary change.
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