1. Change Over Time Galapagos Islands
Read the lesson title aloud.
Galapagos Islands

2. Learning Objectives
Describe how Darwin’s observations helped him to develop his hypothesis.
Explain the process of natural selection and how it contributes to evolution.
Click to show each learning objective.
Make sure that students understand the difference between Darwin’s theory of evolution and his hypothesis about natural selection. Point out that Darwin’s hypothesis was an explanation for the observations he had made while traveling on the Beagle. Darwin’s theory of evolution was based on his hypothesis about natural selection.
Make sure that students know that at the end of the presentation, they should understand Darwin’s hypothesis and the relationship between evolution and natural selection.

3. Who Was Charles Darwin?
In 1839, Charles Darwin published his book The Voyage of the Beagle.
Ask: What do you know about Charles Darwin?
Encourage students to share their responses.
Click to reveal the fact.
Tell students that in 1831, Charles Darwin made an important voyage to the Galápagos Islands. His observations on the islands were later published in a book called The Voyage of the Beagle.
Explain to students that the observations Darwin made during the Beagle’s voyage led him to develop one of the most important scientific theories of all time.
Ask: Who can tell the class about a time you visited a new place where you saw animals or plants you had never seen before?
Sample answer: Students may describe different kinds of grasses, flowers, trees, birds, and deer or other mammals they saw on a trip.
Helped him develop one of the most important scientific theories of all time.

4. Scientific Theory
A well tested concept that explains a wide range of observations

5. Darwin’s Hypothesis
Darwin was a naturalist—someone who observes and studies the natural world.
Giant ground sloth
Read the fact about Darwin aloud.
Explain to students that Darwin was amazed by the diversity of living things that he observed during his voyage. He wondered why they were so different from living things in England. Today, scientists know that organisms are even more diverse than Darwin thought. In fact, scientists have identified about 1.3 million species of eukaryotic organisms. Explain that a species is a group of similar organisms that can mate with one another and produce fertile offspring.
Explain that Darwin’s observations on the Galápagos Islands led him to question whether all living things were created at the same time and whether living things never changed. One of the animals Darwin observed were sloths, slow-moving animals that spent much of their time hanging in trees. Darwin also saw fossils of animals that had died long ago.
Tell students that a fossil is the preserved remains or traces of an organism that lived in the past. Explain to students that Darwin observed that some of the fossils resembled the bones of living sloths but were much larger. He wondered what had happened to the ancient, giant ground sloths.
Click to reveal two pictures.
Ask students to identify which is the modern-day sloth and which is the giant ground sloth. Have a volunteer point to the appropriate pictures.
Click to reveal the correct labels.
Click to reveal two pictures of skeletons.
Ask students to compare and contrast the two skeletons.
Ask: What is similar about the skeletons of these two species? What is similar about the pictures of the actual animals?
Sample answers: Both animals have fur; both have limbs for climbing.
Modern-day sloth

6. The Galápagos Organisms
Darwin became convinced that species do not always stay the same.
Ask a student to read the statement aloud.
Explain to students that Darwin thought species could change and even produce new species over time.
Tell students that islands are good places for studying how organisms change over time. Point out that the Galápagos Islands are isolated from mainland South America. Point out that Darwin concluded that animals on the islands came from the mainland but had changed over time.
Explain to students that Darwin noticed that the differences between the island species and the mainland species increased each species’ ability to survive and reproduce in their particular environment.
Click to reveal the two photos of the iguanas.
Explain to students that the iguanas on the Galápagos Islands have large claws that allow them to grip slippery rocks so they can feed on seaweed. The iguanas on the mainland have smaller claws that allow them to climb trees so they can eat leaves. He also noticed that each species’ color helped them blend in better with their habitat.
Ask: Which of these iguanas did Darwin observe on the Galápagos Islands and which did he observe on the mainland of South America?
Ask a student point to the Galápagos Islands iguana.
Click to reveal the answer.
Ask: What can you observe about the coloring of these two iguanas?
Answer: The island iguana is the same color as the soil or rock it is standing on. The mainland iguana does not match the color of the object it is standing on, but its green color would match the leaves of trees.
Galápagos Island iguana
Mainland iguana

7. The Galápagos Finches
The structure of the Galápagos finch beaks is an adaptation to the type of food each bird eats.
Tell students that Darwin noticed that the birds on the Galápagos Islands were different from one island to the next. When Darwin returned to England, he learned that the different birds were all finches. Darwin concluded that the finch species were all related to a single ancestor species that came from the mainland. Over time, different finches developed different beak shapes and sizes that were well suited to the food that they ate.
Tell students to look at the diagram of the finches.
Ask: What are some specific differences among the finches’ beaks?
Sample answer: The beaks differ in their size and how pointed they are. The medium ground finch has the widest beak. The cactus ground finch has the longest, most pointed beak.
Ask: How would you match each finch to the type of food it eats?
Have a student draw arrows between each finch and the type of food it eats.
Click to reveal the correct answers.
Ask a student to read the statement at the top of the slide.
Tell students that an adaptation is a trait that increases an organism’s ability to survive and reproduce.
Make sure that students understand the difference between the everyday use of the words “adapt” and” adaptation” and the scientific use of these words. Encourage students to say that people adjust, rather than adapt, to changes. Stress that, in science, adapting is not a choice that an organism makes. The Galápagos iguana did not get heavier claws and brown skin because it wanted or needed them.
Explain to students that Darwin formulated his hypothesis after observing adaptations that helped organisms survive and reproduce in different environments. Darwin reasoned that organisms that arrived on the islands faced conditions that were different from those on the mainland. Over many generations, the species became better adapted to the new conditions. These ideas came to be known as the theory of evolution.

8. Selective Breeding
In Selective Breeding only the organisms with a desired characteristic are bred.

9. Natural Selection
The process by which individuals that are better adapted to their environment are more likely to survive and reproduce

10. Three main points of natural selection
Overproduction
Competition
Variation

11. Overproduction
Darwin observed that most species produce far more offspring than can survive.
In many species there’s not enough resources, food, water, and living space.

12. Competition
Food , space, and other resources are limited, so members of species must compete for survival
Competition is not always physical, it is usually indirect.
Ex. Some turtles are better at finding food then others
A slower turtles may be caught by a predator while a faster one can escape.

13. Variation Any difference between individuals of the same species.
Ex. Sea turtles may differ in color, size, the ability to swim quickly, and shell hardness

14. Natural Selection Overproduction Competition Variation
Examine the sequence below that shows how natural selection could affect a group of sea turtles over time.
Overproduction
Competition
Variation
Explain to students that Darwin proposed that evolution occurs by means of natural selection. He believed natural selection occurs over a long period of time. Darwin described this process in 1858 in the book The Origin of Species.
Tell students that Darwin identified three factors that affect the process of natural selection: overproduction, competition, and variation.
Tell students that the diagram shows how natural selection can affect a group of sea turtles over time. Explain to students that sea turtle hatchlings are especially vulnerable because they are very small and easy for predators to grab. They hatch on the beach and have to cross the sand to get to the water. Birds and crabs can catch them before they get into the water.
Ask: Which hatchlings are most likely to survive?
Answer: the ones that can move most quickly
Ask: As the turtles grow up, which are the most likely to survive?
Sample answer: the ones that can swim fast and get away from predators; the ones that can find food
Tell students that sea turtles and many other species produce more offspring than can survive.
Ask a student to circle the part of the diagram demonstrates the idea of overproduction.
Click to reveal the label Overproduction.
Explain that overproduction leads to competition among offspring because there are more individuals than there is food to consume and more individuals than there are places for animals to hide and rest. Since food, space, and other resources are limited, the members of a species must compete with one another to survive. A slower turtle may be caught by a predator, while a faster turtle may escape. Only some turtles will survive to reproduce.
Ask a student to circle the part of the diagram that demonstrates the idea of competition.
Click to reveal the label Competition.
Explain that members of a species differ from one another in many of their traits. Sea turtles may differ in color, size, the ability to swim quickly, and shell hardness. Some sea turtles may be protected by having harder shells.
Ask a student to circle the part of the diagram that demonstrates the idea of variation.
Click to reveal the label Variation.
Ask: In addition to survival, what else must happen for natural selection to affect the evolution of the species?
Answer: The individuals that survive must reproduce and pass on their adaptations to their offspring.
Discuss this idea as it applies to the diagram and check for understanding.

15. Species
A group of similar organisms that can mate with each other and produce offspring.

16. Adaptation
Adaptation – an inherited behavior or physical characteristic that helps an organism survive and reproduce in its environment

17. Change Over Time Overview
An adaptation is a trait that increases an organism’s ability to
and
2. The different shapes of bird beaks are examples of
survive
reproduce
adaptation
Ask a volunteer to read each statement aloud. Have students complete the statements using terms from the word bank.
Click to reveal the correct answers.
survive natural selection evolution competition
reproduce adaptation

18. Student Worksheet Answers
Distribute the worksheet to students. Have them create their own graphic organizer to describe the evidence that supports the theory of natural selection.
If students need additional support, help reinforce understanding about a theory.
A hypothesis is a possible explanation for observations made by scientists or an answer to a scientific question. Scientists must carry out investigations and gather evidence that either supports or disproves the hypothesis. Identifying the supporting evidence for a hypothesis or theory can help you understand the hypothesis or theory. Evidence consists of facts—information whose accuracy can be confirmed by testing or observation.
Have students compare their graphic organizers with a partner. Tell students to add any missing pieces of supporting evidence.
Worksheet Answers:
Natural Selection: The process by which individuals that are better adapted to their environment are more likely to survive and produce more offspring than other members of the same species
Evidence: Fossil evidence: living organisms resemble fossilized remains
Evidence: Darwin observed that species on the Galápagos Islands were similar to and different from mainland species. Darwin suggested that species had adapted to the island environment.
Evidence: Darwin studied animals produced by selective breeding to study how evolution might work.
Evidence: In species that overproduce, the offspring that survive are those that are best adapted to the environment.