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CHAPTER
9 Theory of Evolution
Learning Objectives
• Define evolution.
• Describe the significance of the voyage of the HMS Beagle.
• Summarize Darwin’s finding on the Galápagos Islands.
Darwin’s Theory of Evolution
1. Who was Charles Darwin?
Do you ever wonder why some birds are big like ostriches and some
birds are small like robins? Or why a lion has a mane while a leopard
has spots? In the 19th century, an English natural scientist named
Charles Darwin was also fascinated by the diversity of life on Earth.
2. What does the word “evolution”
He set out to answer the following questions: mean?
• Why are organisms different?
• Why are organisms similar?
• Why are there so many different types of organisms?
3. The theory of evolution states that
To answer his questions, he developed what we now call "the theory of organisms come from where?
evolution by natural selection." This theory is one of the most important
theories in the field of life science. In everyday English, "evolution"
simply means "change." In biology, evolution states that all living
organisms came from earlier forms of life. Darwin spent over 20 years
4. What does the Theory of Evolution by
traveling around the world and making observations before he fully
Natural Selection explain?
developed his theory. The Theory of Evolution by Natural Selection
explains how evolution occurs, or how organisms change over time.
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Voyage of the Beagle
In 1859, Charles Darwin published his book, On the Origin of Species 5. What was the name of Darwin’s book?
by Means of Natural Selection (often known as The Origin of Species).
His book describes the observations and evidence that he collected
more than 20 years of research, beginning with a five-year voyage
around the world on a British research ship, the HMS Beagle. During
the voyage, Darwin made observations about plants and animals around
the world. He also collected specimens to study for when he returned to
England, many of those specimens for finches and insects he collected
from the Galapagos islands.
Each time the HMS Beagle stopped at a port, Darwin went on land to 6. What was the name of the ship that
explore and look at the local plants, animals, and fossils. One of the Darwin travelled on?
most important things Darwin did was keep a diary. He took detailed
notes and made drawings of his observations.
7. How did Darwin keep track of his
observations and travels?
The Galápagos Islands
While the crew of the HMS Beagle mapped the coastline of South 8. Where is the Galapagos islands?
America, they traveled to a group of islands called the Galápagos, off
the west coast of South America.. Darwin spent months on foot
exploring the islands. The specimens he collected from the Galápagos
and sent back to England greatly influenced his ideas of evolution
On the Galápagos, Darwin observed that the same kind of animal
differed from one island to another. For example, members of one
iguana species spent most of their time in the ocean, swimming and
diving underwater for seaweed, while those of another iguana species
lived on land and ate cactus. Darwin wondered why there were two
species of iguanas on the same set of islands that were so different from 9. What did Darwin notice about the
iguanas on the islands?
one another.
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Giant Tortoises
Darwin also observed giant tortoises on the Galápagos (Figure 1.5). 10. Describe the tortoises that ate plants
These tortoises were so large that two people could ride on them. near to the ground.
Darwin noticed that different tortoise species lived on islands with
different environments. He realized that the tortoises had traits that
allowed them to live in their particular environments. For example,
tortoises that ate plants near the ground had rounded shells and shorter
necks.
Tortoises on islands with tall shrubs had longer necks and shells that
bent upward, allowing them to stretch their necks . Darwin began to
hypothesize that organisms developed traits over time because of 11. Describe the tortoises that lived on
differences in their environments. Darwin began to think that islands that had tall shrubs and
organisms evolved adaptations that allowed them to live in their vegetation.
environment. Adaptations are favorable traits that give organisms an
advantage for survival and reproduction.
12. The observations of the tortoises lead
Darwin to what hypothesis?
The name “Galápagos” means “giant tortoise.” When Darwin arrived on the
Galápagos Islands, he was amazed by the size and variety of shapes of these 13. What is an adaptation?
animals. The giant tortoise is a unique animal found only in the Galápagos
Islands. There are only about 200 tortoises remaining on these islands.
Darwin’s Finches
The most studied animals on the Galápagos are finches, a type of bird..
Each island had its own distinct species of finch. The birds on different
14. What does the word “Galapagos”
islands had many similarities, but their beaks differed in size and shape. mean?
In his diary, Darwin described how the shapes of the finch beaks on
each island were well-matched with the seeds available on that island,
but not the seeds on other islands. For example, a larger and stronger
beak was needed to break open large seeds on one island, and a small
beak was needed to eat the small seeds on a different island.
15. What observation did Darwin make
about finches found on the islands?
