1. II. Ideas That Shaped Darwin’s Thinking
*During Darwin’s time, Europeans believed :
1. The Earth & all of its creatures had only been created a few thousand years ago.
2. Neither the planet nor its organisms had changed.
3. Rocks had been produced suddenly in catastrophic events.
4. The fossil record was a result of many periods of creation.
-Based on evidence that he had seen,
observations, & literature he had read,
Darwin didn’t accept these beliefs.

2. A. An Ancient Changing Earth
*Scientists studying the world
gathered data that suggested that
Earth was very old & had changed
slowly over time.
-Scientists James Hutton & Charles
Lyell helped scientists recognize
that Earth is many millions of
years old, & the processes that
changed Earth in the past are the
same processes that operate in
the present.

3. Hutton & Geologic Change
1795 – James Hutton (geologist)
publishes a hypothesis about
the geological forces that have
shaped Earth.
He proposed that :
1. Layers of rock form very slowly.
2. Some rocks are moved up by forces beneath Earth’s surface, others are buried, & others are pushed up from the sea floor to form mountain ranges.
3. Resulting rock is shaped by natural forces, ex : rain, wind, heat, cold.

4. Lyell’s Principles of Geology :
-Charles Lyell (geologist) published a
book (Principles of Geology) that
Darwin received shortly before the
voyage of the Beagle.
Lyell stated that :
1. Scientists must explain past events
in terms of processes that can be
observed.
2. Geologic features can be built up/
torn down over long periods of time.

5. Lyell’s Impact on Darwin
*Lyell helped Darwin appreciate
the significance of geologic
phenomena he’d seen, ex :
volcanoes/earthquakes.
Lyell affected Darwin in 2 ways :
1. He wondered if Earth can change over time, can animals?
2. If possible, it would have taken many years for life to change.

6. B. Lamarck’s Evolution Hypothesis
Jean-Baptiste Lamarck – French
naturalist who was among the
first scientists to recognize that
living things have changed over
time.
1809 – Lamarck publishes his
hypothesis, which states that :
1. By selective use or disuse of
organs, organisms acquired or lost certain traits during their lifetime.
2. These traits could then be passed on to offspring.
3. Over time, this process led to
changes in a species.

7. Major Points in Lamarck’s Hypothesis :
1. Tendency toward perfection – all organisms have innate tendency toward complexity & perfection, resulting in change & develop of new features that help them live more successfully.
2. Use & Disuse – abilities of organisms to change size/shape of organs by using their bodies in new ways, ex : legs becoming wings or wings disappearing because unused.
3. Inheritance of Acquired Traits – changes that organisms acquire get passed down to their offspring, ex : lifting weights & getting big muscles.
Problems with Lamarck’s Ideas :
1. Behavior has no effect on an organism’s heritable characteristics.
2. Traits aren’t inherited the way that he suggests.

8. Lamarck’s Giraffes

9. C. Malthus & Population Growth
Thomas Malthus – English
economist who wrote a book
about human population growth.
He reasoned that :
1. If the human population continued
growing, it would eventually
run out of resources ex : food.
2. Forces work against growth
to control population size,
ex : war, famine, & disease.
*Darwin believed that Malthus’s
principles applied more strongly
to plants & animals because they
produce far more offspring
more quickly than people do.