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Ch 15 Darwin’s Theory of Evolution
15-1 The Puzzle of Life's Diversity
A. Introduction
1. Evolution- or change over time, is the process by which modern organisms have descended from ancient
organisms.
2. A scientific theory is a well-supported testable explanation of phenomena that have occurred in the
natural world.
a. EX: electromagnetic theory or the theory of relativity
B. Voyage of the Beagle
1. In 1831, Darwin set sail from England aboard the H.M.S. Beagle for a voyage around the world.
2. Darwin went ashore and collected plant and animal specimens for his collection.
3. He studied the specimens, read the latest scientific books, and filled many notebooks with his
observations and thoughts.
C. Darwin’s Observations
1. During his travels, Darwin made numerous observations and collected evidence that led him to propose
a hypothesis about the way life changes over time.
2. That hypothesis has become the theory of evolution.
3. Darwin observed that many plants and animals were well suited to the environments they inhabited.
4. He was impressed by the ways in which organisms survived and produced offspring.
5. Darwin was puzzled by where different species lived and did not live.
6. Grasslands in some regions were similar to one another but were inhabited by very different animals.
D. Living Organisms and Fossils
1. Darwin collected the preserved remains of ancient organisms, called fossils.
2. Some of those fossils resembled organisms that were still alive.
3. Others looked completely unlike any creature he had ever seen.
E. The Galápagos Islands
1. Darwin observed that the Galápagos Islands were close together but had very different climates.
2. Darwin observed that the characteristics of many animals and plants varied noticeably among the
different islands of the Galápagos.
3. Darwin wondered if animals living on different islands had once been members of the same species.
4. These separate species would have evolved from an original South American ancestor species.
Activity Galápagos Tortoises 
When Charles Darwin visited the Galápagos
Islands, he discovered that similar animals that
lived on separate islands had different features
~ The tortoises eat plants. On one island, plants
grew very close to the ground. Which of the 3
islands is this likely to be?
~ Which of the 3 islands most likely has sparse
vegetation that is hard to reach?
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15-2 Ideas That Shaped Darwin’s Thinking
A. An Ancient Changing Earth
1. In Darwin’s day, most Europeans thought Earth and all of its life-forms had existed for only a few
thousand years.
2. They also thought that species did not change
3.
Hutton and Lyell helped scientists recognize that Earth is many millions of years old, and that it had
changed over time.
B. Lamarck’s Evolution Hypothesis
1. Jean-Baptist Lamarck was one of the first scientists to see that evolution occurred
2. He also recognized that organisms adapt to their environment
3.
Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits
during their lifetime.
4. These traits could then be passed on to their offspring
C. Population Growth
1.
Economist Thomas Malthus thought that if the human population kept growing, sooner or later there
would be insignificant living space and food for everyone.
15-3 Darwin Presents His Case
A. Publication
1. Darwin published On the Origin of Species in 1859
2. Darwin’s theory was based on artificial selection. In artificial selection, nature provided the variation,
and humans selected those variations that they found useful.
a. EX: animal breeders used only the largest hogs, fastest horses, or cows that produced the most
milk for breeding
B. Evolution by Natural Selection
1. Darwin thought that a similar process occurs in nature.
2. He called this natural selection. This process can be summed up as follows:
a. Individuals differ, and some differences can be passed onto their offspring
b. More offspring are produced than can survive and reproduce
c. There is competition for limited resources, or a struggle for existence
d. Individuals best suited to their environment survive and reproduce most successfully. “Survival
of the fittest”
3. Fitness- the ability to survive and reproduce in any given environment.
a. Results from adaptations
4. Adaptations- inherited traits that increase an organism’s chance of survival.
a. Only the fittest organisms pass on their traits
b. Because of this, species change over time
5. Darwin argued that species alive today descended with modification from species of the past.
6. Common descent- this principle states that all species come from common ancestors
7. The principle of common descent link all organisms on Earth into a single tree of life.
C. Evidence of Evolution
1. Darwin argued that living things have been evolving on Earth for millions of years. He presented four
types of evidence in support of evolution.
a. The fossil record
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i. Comparing fossils from older and younger rock layers provides evidence that evolution
has taken place
b. Geographic distribution of living organisms
i. Homologous structures have different mature forms but develop from the same
embryonic tissues.
ii. Provide strong evidence that organisms have descended, with modifications, from
common ancestors.
iii. Some homologous structures no longer serve major roles in descendents.
iv. If the structures are greatly reduced in size, they are called vestigial structures
1. EX: appendix in humans – carries out no function in digestion
2. EX: hip bones in snakes and whales
c. Similarities in early development
i. The early stages, or embryos, of many animals are very similar.
ii. These similarities are evidence that the animals share common ancestors
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