1 Changes Over Time Section Summary Darwin s Theory Key Concepts What important observations did Darwin make on his voyage? What hypothesis did Darwin make to explain the differences between similar species? How does natural selection lead to evolution? In 1831, Charles Darwin left England on board the HMS Beagle. Darwin s important observations included the diversity of living things, the remains of ancient organisms, and the characteristics of organisms on the Galápagos Islands. Darwin saw many different species. A species is a group of similar organisms that can mate with each other and produce fertile offspring. Darwin saw the fossil bones of animals that had died long ago. A fossil is the preserved remains or traces of an organism that lived in the past. In 1835, the Beagle reached the Galápagos Islands in the Pacific Ocean. Darwin was surprised that many of the plants and animals on the Galápagos Islands were similar to organisms on mainland South America. However, there were also important differences. Darwin inferred that a small number of different species had come to the islands from the mainland. Eventually, their offspring became different from the mainland relatives. The finches on the Galápagos Islands were noticeably different from one island to another. The most obvious differences were the varied sizes and shapes of the birds beaks. Beak shape is an example of an adaptation, a trait that helps an organism survive and reproduce. Darwin reasoned that plants or animals that arrived on the Galápagos Islands faced conditions that were different from those on the mainland. Perhaps, Darwin hypothesized, the species gradually changed over many generations and became better adapted to the new conditions. The gradual change in a species over time is called evolution. Darwin s ideas are often referred to as the theory of evolution. A scientific theory is a well-tested concept that explains a wide range of observations. In his book The Origin of Species, Darwin proposed that evolution occurs by means of natural selection. Natural selection is the process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species. A number of factors affect the process of natural selection: overproduction, competition, and variations. Any difference between individuals of the same species is called a variation. Some variations make certain individuals better adapted to their environment because of helpful traits they possess. Darwin proposed that, over a long period of time, natural selection can lead to change. Helpful variations may gradually accumulate in a species, while unfavorable ones may disappear. Without variations, all members of a species would have the same traits. Only traits that are inherited, or controlled by genes, can be acted upon by natural selection.
2 Changes Over Time Name Date Class Changes Over Time Guided Reading and Study Darwin s Theory This section discusses Charles Darwin and his theories of evolution, which are based on what he saw during his trip around the world. Use Target Reading Skills In the graphic organizer, identify factors that cause natural selection. Causes Overproduction: More offspring than can survive Effect Natural Selection Darwin s Observations 1. Is the following sentence true or false? Charles Darwin was not surprised by the variety of living things he saw on his voyage around the world. 2. A group of similar organisms that can mate with each other and produce fertile offspring is called a(n). 3. A(n) is the preserved remains or traces of an organism that lived in the past. 4. Is the following sentence true or false? Darwin observed the greatest diversity of organisms on the Galápagos Islands.
3 Changes Over Time Guided Reading and Study Darwin s Theory (continued) Galápagos Organisms 5. Circle the letter of each sentence that is true about Darwin s observations. a. Many Galápagos organisms were similar to organisms on mainland South America. b. Iguanas on the Galápagos Islands had small claws for climbing trees. c. Darwin thought the ancestors of Galápagos animals and plants came from mainland South America. d. All tortoises living in the Galápagos Islands looked exactly the same. 6. Darwin noticed many differences among similar as he traveled from one Galápagos island to the next. Look at the bird beaks below. Match the bird beaks with the kind of food the bird eats. Kind of Food Bird Beaks 7. insects 8. seeds a. b. 9. A trait that helps an organism survive and reproduce is a(n). Evolution 10. Circle the letter of each sentence that is true about Darwin s conclusions. a. Darwin understood immediately why Galápagos organisms had many different adaptations. b. Darwin thought that Galápagos organisms gradually changed over many generations. c. Darwin believed that evolution had occurred on the Galápagos Islands. d. Selective breeding helped Darwin understand how evolution might occur.
4 Changes Over Time Name Date Class Changes Over Time Guided Reading and Study 11. Circle the letter of the term that means a well-tested concept that explains many observations. a. idea b. evolution c. scientific theory d. hypothesis Natural Selection 12. In his book The Origin of Species, Darwin explained that evolution occurs by means of. 13. Is the following sentence true or false? Individuals with variations that make them better adapted to their environment will not survive. Match the factors that affect the process of natural selection with their definitions. Definitions 14. Effect caused by limited food and other resources. 15. Differences between individuals of the same species 16. Effect caused by species producing more offspring than can survive. Factors a. overproduction b. competition c. variations 17. Is the following sentence true or false? Only traits that are controlled by genes can be acted upon by natural selection. 18. Is the following sentence true or false? Darwin knew all about genes and mutations.
5 Changes Over Time Review and Reinforce Darwin s Theory Understanding Main Ideas Answer the following questions on a separate sheet of paper. 1. Who was Charles Darwin, and what did he do on the Beagle s voyage? 2. What is evolution? 3. Explain how the shape of a finch s beak is an example of an adaptation. 4. When members of a species compete, what do they compete for? 5. What happens when species overproduce offspring? 6. Suppose a variation makes an individual member of a species better adapted to its environment. How might that variation affect the individual s reproduction? 7. How does the environment select organisms? 8. How do helpful variations accumulate in a species over time? 9. Why can only traits controlled by genes be acted upon by natural selection? Building Vocabulary Fill in the blank to complete each statement. 10. A(n) is a group of similar organisms that can mate with each other and produce fertile offspring. 11. A(n) is a trait that helps an organism survive and reproduce. 12. A scientific is a well-tested concept that explains a wide range of observations. 13. The process by which individuals that are better adapted to their environment are more likely to survive and reproduce is called. 14. That some newly hatched turtles can swim faster than others of the same species is evidence of within the species.
6 Changes Over Time Name Date Class Changes Over Time Enrich Two Theories of Evolution If you had been a biologist in the 1800s, you would have had to decide between two main theories about how evolution occurred. Consider the long neck of a giraffe. How did that evolve? Read the two explanations below, and then answer the questions that follow. Theory 1 The ancestors of giraffes had short necks, and there was great competition for the plant food near the ground. Some of the giraffes kept trying to stretch their necks to reach leaves higher in the trees. As they stretched and stretched, their necks became longer. As their necks became longer, they were able to reach more food. Those ancestral giraffes survived to reproduce, while the giraffes that had not stretched their necks died. The offspring of giraffes with stretched necks inherited the longer necks. This process continued for generation after generation. In this way, giraffes evolved with longer and longer necks. Theory 2 The ancestors of giraffes had short necks, and there was great competition for the plant food near the ground. Some of the ancestral giraffes naturally had slightly longer necks than others. The individuals with longer necks could reach leaves higher up in trees, and therefore could eat more food. Because those ancestral giraffes ate more food, they survived to produce offspring while the individuals with shorter necks did not. The offspring of giraffes with longer necks inherited the longer necks. This process continued for generation after generation. In this way, giraffes evolved with longer and longer necks. Answer the following questions on a separate sheet of paper. 1. In Theory 1, what caused the giraffe neck to become longer? 2. In Theory 2, what caused the giraffe neck to become longer? 3. According to what scientists now know about genes, could the giraffes offspring have inherited longer necks as described in Theory 1? As described in Theory 2? Explain. 4. Which of the two theories matches Darwin s theory of evolution? Explain.
7 Changes Over Time Skills Lab Nature at Work Problem How do species change over time? Skills Focus predicting, making models Materials scissors marking pen construction paper, 2 colors Procedure 1. Work on this lab with two other students. One student should choose construction paper of one color and make the team s 50 mouse cards, as described in Table 1. The second student should choose a different color construction paper and make the team s 25 event cards, as described in Table 2. The third student should record all the data. PART 1 A White Sand Environment 2. Mix up the mouse cards. 3. Begin by using the cards to model what might happen to a group of mice in an environment of white sand dunes. Choose two mouse cards. Allele pairs WW and Ww produce a white mouse. Allele pair ww produces a brown mouse. Record the color of the mouse with a tally mark in the data table on the next page. 4. Choose an event card. An S card means the mouse survives. A D or a P card means the mouse dies. A C card means the mouse dies if its color contrasts with the white sand dunes. (Only brown mice will die when a C card is drawn.) Record each death with a tally mark in the data table. 5. If the mouse lives, put the two mouse cards in a live mice pile. If the mouse dies, put the cards in a dead mice pile. Put the event card at the bottom of its pack. 6. Repeat Steps 3 through 5 with the remaining mouse cards to study the first generation of mice. Record your results. 7. Leave the dead mice cards untouched. Mix up the cards from the live mice pile. Mix up the events cards. 8. Repeat Steps 3 through 7 for the second generation. Then repeat Steps 3 through 6 for the third generation.
8 Changes Over Time Name Date Class Changes Over Time Skills Lab Mouse Cards Number Label Meaning 25 W Dominant allele for white fur 25 w Recessive allele for brown fur Number Label Meaning 5 S Mouse survives. Event Cards 1 D Disease kills mouse. 1 P Predator kills mice of all colors. 18 C Predator kills mice that contrast with the environment. Data Table Part 1 Type of Environment: Population Deaths Generation White Mice Brown Mice White Mice Brown Mice Data Table Part 2 Type of Environment: Population Deaths Generation White Mice Brown Mice White Mice Brown Mice 1 2 3
9 Changes Over Time Skills Lab Nature at Work (continued) PART 2 A Forest Floor Environment 9. How would the data differ if the mice in this model lived on a dark brown forest floor? Record your prediction in the space provided. 10. Use the cards to test your prediction. Remember that a C card now means that any mouse with white fur will die. Analyze and Conclude Write your answers on a separate sheet of paper. 1. Calculating In Part 1, how many white mice were there in each generation? How many brown mice? In each generation, which color mouse had the higher death rate? (Hint: To calculate the death rate for white mice, divide the number of white mice that died by the total number of white mice, then multiply by 100%.) 2. Predicting If the events in Part 1 occurred in nature, how would the group of mice change over time? 3. Observing How did the results in Part 2 differ from those in Part 1? 4. Making Models How would it affect your model if you increased the number of C cards? What would happen if you decreased the number of C cards? 5. Communicating Imagine that you are trying to explain the point of this lab to Charles Darwin. Write an explanation that you could give to him. To prepare to write, answer the following questions: What are some ways in which this investigation models natural selection? What are some ways in which natural selection differs from this model? Design an Experiment Choose a different species with a trait that interests you. Make a set of cards similar to these cards to investigate how natural selection might bring about the evolution of that species. Obtain your teacher s permission before carrying out your investigation.
10 Changes Over Time Section Summary Evidence of Evolution Key Concepts What evidence supports the theory of evolution? How do scientists infer evolutionary relationships among organisms? How do new species form? Modern-day organisms can provide clues about evolution. Fossils, patterns of early development, and similar body structures all provide evidence that organisms have changed over time. By comparing organisms, scientists can infer how closely related the organisms are in an evolutionary sense. Scientists compare body structures, development before birth, and DNA sequences to determine the evolutionary relationships among organisms. Scientists make inferences about evolutionary relationships by comparing the early development of organisms. An adult opossum, chicken, salamander, and fish look quite different; however, during early development these four organisms are similar. These similarities suggest that these vertebrate species are related and share a common ancestor. An organism s body structure is its basic body plan, such as how its bones are arranged. Fishes, amphibians, reptiles, birds, and mammals, for example, all have a similar body structure an internal skeleton with a backbone. This is why scientists classify all five groups of animals together as vertebrates. Presumably, these groups all inherited these similarities in structure from an early vertebrate ancestor that they shared. Similar structures that related species have inherited from a common ancestor are called homologous structures. Sometimes scientists find fossil evidence that supports the evidence provided by homologous structures. Scientists infer that species with similar body structures and development patterns inherited many of the same genes from a common ancestor. Recall that genes are made of DNA. By comparing the sequences in the DNA of different species, scientists can infer how closely related the species are. The more similar the sequences, the more closely related the species are. Recall also that the DNA bases along a gene specify what type of protein will be produced. Therefore, scientists can also compare the order of amino acids in a protein to see how closely related two species are. Scientists have combined the evidence from DNA, protein structure, fossils, early development, and body structure to determine the evolutionary relationships among species. In most cases, DNA and protein sequences have confirmed conclusions based on earlier evidence. Scientists use such combined evidence to construct branching trees. A branching tree is a diagram that shows how scientists think different groups of organisms are related. Isolation, or complete separation, occurs when some members of a species become cut off from the rest of the species. A new species can form when a group of individuals remains separated from the rest of its species long enough to evolve different traits.
11 Changes Over Time Name Date Class Changes Over Time Guided Reading and Study Evidence of Evolution This section tells how scientists decide which living things are related. Use Target Reading Skills As you read, identify the evidence that supports the theory of evolution. Write the evidence in the graphic organizer. Evidence Fossils Theory Evolution Interpreting the Evidence 1. Similar body structures that related species have inherited from a common ancestor are called. 2. What similarities in development lead scientists to infer that opossums, chickens, salamanders, and fish share a common ancestor? 3. Why do scientists classify fish, amphibians, reptiles, birds, and mammals together in one group?
12 Changes Over Time Guided Reading and Study Evidence of Evolution (continued) Inferring Species Relationships 4. Is the following sentence true or false? The more closely related species are, the more similar their DNA sequences. 5. What have scientists learned about the elephant shrew based on DNA evidence? 6. Circle the letter of each sentence that is true about evolutionary relationships of organisms. a. DNA comparisons show that dogs are more similar to coyotes than to wolves. b. Scientists can compare protein structure to determine how closely two species are related. c. A branching tree shows how scientists think different groups of organisms are related. d. DNA evidence shows that giant pandas are more closely related to raccoons than to bears. 7. Is the following sentence true or false? When a group of individuals remains isolated from the rest of its species long enough to evolve different traits, a new species can form. 8. What are three ways that isolation can occur?
13 Changes Over Time Name Date Class Changes Over Time Review and Reinforce Evidence of Evolution Understanding Main Ideas Use the figures below to answer the questions that follow. Write your answers on a separate sheet of paper. Seal Bird 1. Compare and contrast the bones of a bird s wing and a seal s flipper. 2. What do scientists infer from the similarities between these two structures? 3. What do scientists call such similar structures? 4. Describe how DNA evidence might be used to confirm scientists conclusions about any relationship between birds and seals. Answer the following questions on a separate sheet of paper. 5. What types of evidence do scientists use to determine evolutionary relationships among groups? 6. What do similarities in the early development of organisms suggest? Building Vocabulary Fill in the blank to complete each statement. 7. Similar structures that related species have inherited from a common ancestor are called structures. 8. A(n) is a diagram that shows how scientists think different groups of organisms are related.
14 Changes Over Time Enrich Species Relationships Mammals Jawless fishes Sharks and their relatives Amphibians Bony fishes Reptiles Birds Use the figure above to answer the following questions. Write your answers on a separate sheet of paper. 1. What is this type of diagram called, and what is the purpose of such a diagram? 2. What types of evidence did scientists use to make this diagram? 3. Did amphibians evolve from reptiles? Give evidence for your answer. 4. Are birds more closely related to mammals or to reptiles? Explain your answer. 5. What could cause scientists to change the information on this diagram in the future?
15 Changes Over Time Name Date Class Changes Over Time Skills Lab Telltale Molecules Problem What information can protein structure reveal about evolutionary relationships among organisms? Skills Focus interpreting data, drawing conclusions Procedure 1. Examine the table below. It shows the sequence of amino acids in one region of a protein, cytochrome c, for six different animals. 2. Predict which of the five other animals is most closely related to the horse. Which animal do you think is most distantly related? 3. Compare the amino acid sequence of the horse to that of the donkey. How many amino acids differ between the two species? Record that number in your notebook. 4. Compare the amino acid sequences of each of the other animals to that of the horse. Record the number of differences in your notebook. Section of Cytochrome c Protein in Animals Animal Amino Acid Position Horse A B C D E F G H I J K L M N O Donkey A B C D E F G H Z J K L M N O Rabbit A B C D E Y G H Z J K L M N O Snake A B C D E Y G H Z J K W M N O Turtle A B C D E V G H Z J K U M N O Whale A B C D E Y G H Z J K L M N O
16 Changes Over Time Skills Lab Telltale Molecules (continued) Analyze and Conclude Write your answers in the spaces provided. 1. Interpreting Data Which animal s amino acid sequence was most similar to that of the horse? What similarities and difference(s) did you observe? 2. Drawing Conclusions Based on these data, which species is most closely related to the horse? Which is most distantly related? 3. Interpreting Data For the entire protein, the horse s amino acid sequence differs from the other animals as follows: donkey, 1 difference; rabbit, 6; snake, 22; turtle, 11; and whale, 5. How do the relationships indicated by the entire protein compare with those for the region you examined? 4. Communicating Write a paragraph explaining why data about amino acid sequences can provide information about evolutionary relationships among organisms. More to Explore Use the amino acid data to construct a branching tree that includes horses, donkeys, and snakes. The tree should show one way that the three species could have evolved from a common ancestor.
17 Changes Over Time Section Summary The Fossil Record Key Concepts How do most fossils form? How can scientists determine a fossil s age? What is the Geologic Time Scale? What are some unanswered questions about evolution? Most fossils form when organisms that die become buried in sediments. Sediments are particles of soil and rock. Layers of sediments cover the dead organism. Over millions of years, the layers harden to become sedimentary rock. Some remains that become buried in sediments are actually changed to rock. These fossils are called petrified fossils. Sometimes shells or other hard parts buried by sediments are gradually dissolved. A hollow space in sediment in the shape of an organism or part of an organism is called a mold. Sometimes a mold becomes filled in with hardened minerals, forming a cast. Organisms can also be preserved in ice. Scientists can determine a fossil s age in two ways: relative dating and radioactive dating. Scientists use relative dating to determine which of two fossils is older. In a sequence of rock layers, the top layers are usually younger than the lower layers. Therefore, fossils found in top layers are younger than fossils found in bottom layers. Another technique, called radioactive dating, allows scientists to determine the actual age of fossils. Rocks near fossils contain radioactive elements, unstable elements that decay, or break down, into different elements. The half-life of a radioactive element is the time it takes for half of the atoms in a sample to decay. Scientists can compare the amount of a radioactive element in a sample to the amount of the element into which it breaks down to calculate the age of the rock. The millions of fossils that scientists have collected are called the fossil record. Despite gaps in the fossil record, it has given scientists a lot of important information about past life on Earth. Almost all of the species preserved as fossils are now extinct. A species is extinct if no members of that species are still alive. Scientists have calculated the ages of many different fossils and rocks. From this information, they have created a calendar of Earth s history that spans more than 4.6 billion years. This calendar of Earth s history is sometimes called the Geologic Time Scale. Two unanswered questions about evolution involve the causes of mass extinctions and the rate at which evolution occurs. A mass extinction occurs when many species become extinct at the same time. Scientists are not sure what causes mass extinctions. There are two theories about the rate of evolution. According to one theory, called gradualism, evolution occurs slowly but steadily. Tiny changes in a species gradually add up to major changes over very long periods of time. According to another theory, called punctuated equilibria, species evolve during short periods of rapid change. Species evolve quickly when groups become isolated and adapt to new environments. Most scientists think that evolution can occur gradually at some times and fairly rapidly at others.
18 Changes Over Time Name Date Class Changes Over Time Guided Reading and Study The Fossil Record This section explains what fossils are and how fossils give clues about evolution. It also describes the Geologic Time Scale, a calendar of Earth's history. Use Target Reading Skills After you read the section, reread the paragraphs that contain definitions of key terms. Use all the information you have learned to write a definition of each key term in your own words. How Do Fossils Form? 1. Circle the letter of each item that can form a fossil. a. bone b. shell c. stone 2. Is the following sentence true or false? Most fossils form when organisms that die become buried in sediments. 3. Particles of soil and rock are called. 4. Remains of organisms that are actually changed to rock are called fossils. 5. Circle the letter of each sentence that is true about molds and casts. a. A mold forms when hard parts of an organism buried by sediments are gradually dissolved. b. A cast is a hollow space in sediment in the shape of an organism. c. A mold that becomes filled in with hardened materials forms a cast. d. A cast is a copy of the shape of an organism. 6. Is the following sentence true or false? The formation of any fossil is a common event.
19 Changes Over Time Guided Reading and Study The Fossil Record (continued) Determining a Fossil s Age 7. Is the following sentence true or false? By determining the age of fossils, scientists can reconstruct the history of life on Earth. 8. In what two ways can scientists determine the ages of fossils? a. b. 9. In layers of sedimentary rock, the layer is usually at the bottom. Each higher layer is than the layers below it. 10. Is the following sentence true or false? Relative dating can only help scientists determine whether one fossil is older than another. 11. Scientists use unstable elements that decay, called elements, to determine the actual age of a fossil. 12. What is the half-life of a radioactive element? 13. Potassium-40 breaks down into over time. 14. How do scientists use radioactive dating to determine the age of a fossil? What Do Fossils Reveal? 15. The millions of fossils that scientists have collected are called the. 16. Is the following sentence true or false? The remains of all organisms have become fossils. 17. How have scientists learned about extinct species?
20 Changes Over Time Name Date Class Changes Over Time Guided Reading and Study 18. Circle the letter of the largest span of time in the Geologic Time Scale. a. Precambrian Time b. eras c. periods d. years 19. Look at the illustration of the Geologic Time Scale in your text. What are the names of the three eras? Unanswered Questions 20. What are mass extinctions? 21. Complete the table below about the two theories of evolution. How Fast Does Evolution Occur? Theory of Evolution What the Theory Says Intermediate Forms of Species? Gradualism Punctuated Equilibria
21 Changes Over Time Review and Reinforce The Fossil Record Understanding Main Ideas Use the figure below to answer questions 1 and 2. Write your answers on a separate sheet of paper. Cenozoic Era Precambrian Time Paleozoic Era Mesozoic Era 1. What is shown in the figure above? 2. What evidence do scientists use to place events on this timeline? Answer the following questions on a separate sheet of paper. 3. Describe the process by which most fossils form. 4. Which is probably older, a fossil in a sedimentary rock layer at the bottom of a canyon or a fossil in a sedimentary rock layer at the top of a canyon? Explain. 5. How do scientists use radioactive elements to determine the actual age of fossils? 6. What is the fossil record, and why is it incomplete? Building Vocabulary Match each term with its definition by writing the letter of the correct definition on the line beside the term. 7. relative dating 8. half-life 9. gradualism 10. radioactive dating 11. extinct 12. sedimentary rock 13. fossil 14. punctuated equilibria a. a species that has no living members b. the preserved remains or traces of an organism that lived in the past c. the theory that species evolve during short periods of rapid change d. a way to determine the actual age of fossils e. rock made of hardened sediment f. the time it takes for half of a radioactive sample to decay g. the theory that evolution occurs slowly but steadily h. a way to determine which of two fossils is older
22 Changes Over Time Name Date Class Changes Over Time Enrich Evolution of Horses Fossil evidence indecates that Hyracotherium is a small animal that lived over 50 million years ago. It is the ancestor of the modern horse, Equus, and many other horselike species that are now extinct. Fossils of these species show differences in body structures. Refer to the table below to answer the following questions. 50 million years ago 35 million years ago 26 million years ago 3 million years ago Hyracotherium Mesohippus Merychippus Equus Forefoot Skull Forefoot Skull Forefoot Skull Forefoot Skull 38 cm at shoulders padded feet lived in dense-forest environment 52 cm at shoulders padded feet lived in mixed woods-and-fields environment 100 cm at shoulders hoofed feet lived in high-grass (savanna) environment 135 cm at shoulders hoofed feet lived in short-grass (prairie) environment Use the table above to answer the following questions. Write your answers on a separate sheet of paper. 1. Use the figure, The Geologic Time Scale, in your textbook to determine the era and period in which Hyracotherium lived. 2. When did Equus first appear in the fossil record? 3. How do the forefeet structures differ among the fossils? 4. How do the skulls differ among the fossils? 5. How might the environment in which each of these species lived have affected the evolutionary history of the horse?
23 Changes Over Time Key Terms Key Terms Answer the clues to solve this crossword puzzle Clues down 1. The gradual change in a species over time 4. A trait that helps an organism survive and reproduce 6. The process by which individuals that are better adapted to their environment are more likely to survive is called natural. 8. A fossil formed when an organism buried in sediment dissolves, leaving a hollow area Clues across 2. Any difference between individuals of the same species 3. The theory that evolution occurs slowly but steadily 5. Similar structures that related species inherited from a common ancestor are structures. 7. The theory that evolution occurs during short periods of rapid change is punctuated. 9. The preserved remains of an organism 10. A group of similar organisms that can mate and produce fertile offspring 11. No members of a species are still alive
24 Changes Over Time Name Date Class Changes Over Time Connecting Concepts Connecting Concepts Develop a concept map that uses the Key Concepts and Key Terms from this chapter. Keep in mind the big idea of this chapter. The concept map shown is one way to organize how the information in this chapter is related. You may use an extra sheet of paper. Evolution is a occurs by means of is supported by evidence such as scientific theory developed by similarities in early development factors that affect it include which selects individuals with overproduction variation which can be viewed by comparing which can be viewed by comparing adaptations which is due to homologous structures fossils which include which allow us to understand which can be broken into petrified fossils casts eras which are shorter which are longer
25 Changes Over Time Laboratory Investigation Variation in a Population Key Concept Variations occur in all species. Skills Focus observing, inferring, measuring, graphing Time 40 minutes Possible Materials (per group) 10 large lima beans 10 leaves of the same species metric ruler graph paper 3 colored pencils Alternate Materials: Other large seeds, such as kidney beans, pumpkin seeds, and pinto beans, may be used instead of the lima beans. Leaves can be from a variety of trees or house plants. Teaching Tips TEACHER NOTES (More to Explore) Students with severe allergies to peanuts should not participate in this activity. (More to Explore) The results for peanuts should be similar to the variations found in the lima bean, leaf, and hand studies. Sample size will influence results. All organisms of the same species show variations in different traits. Heredity and environment both affect how traits vary. Advance Preparation Have students collect leaves before the experiment.
26 Changes Over Time Name Date Class Changes Over Time Laboratory Investigation Variation in a Population Pre Lab Discussion Are you and your friends all exactly alike? Of course not. Although you are all members of one species, you are different in many ways. These differences are called variations and exist in all species. Some variations are inherited by the offspring of an organism. Most inherited variations are neutral, that is, they do not affect the organism s survival. Helpful inherited variations are called adaptations. Harmful inherited variations make the organism less suited to its environment. Better-adapted organisms are more likely to reproduce and pass beneficial traits to their offspring. This process is called natural selection. In this investigation, you will observe variations in two types of plants and in your class population. 1. What does variations mean? 2. What variations exist among members of your class? Problem How can you measure the variation in plant and animal populations? Materials (per group) 10 large lima beans 10 leaves of the same species metric ruler graph paper 3 colored pencils Safety Review the safety guidelines in Appendix A of your textbook. Do not eat the lima beans.
27 Changes Over Time Laboratory Investigation Variation in a Population (continued) Procedure Part A: Variation in Plant Species 1. Obtain 10 large lima beans and 10 leaves of the same species of tree. Blade length 2. Measure the length of each lima bean and leaf blade in millimeters. See Figure 1. Record your measurements, rounded to the nearest millimeter, in Data Table Notice in Figure 1 the petiole of the leaf. Measure the Petiole length length of the petiole of each leaf. Record your measurements, rounded to the nearest millimeter, in Data Table Record on the chalkboard your measurements for each of the plants so that all groups data can be seen. 5. Using data from the entire class, record the range in lengths for the lima beans, leaf blades, and petioles. Record the class findings in Data Tables 2, 3, and 4. Fill in the first row of each table with the lengths, from shortest to longest, using increments of one millimeter. Add more columns to the data tables if necessary. 6. Record the class s total number of each size of lima bean, leaf blade, and petiole in the second row of Data Tables 2, 3, and Using the data in Data Table 2, construct a line graph for the lima bean lengths on a sheet of graph paper. Label the x-axis Lima bean length (mm) and the y-axis Number of beans. 8. Using the data in Data Tables 3 and 4, construct line graphs for the leafblade lengths and the petiole lengths on your graph paper. Label the x-axis Leaf blade and petiole length (mm) and the y-axis Number of leaves. Use a different colored pencil to graph each set of data and include a key for each graph. Figure 1 Part B: Variation in Hand Spans 1. Measure your hand span. The measurement should be made from the top of the thumb to the tip of the little finger, as shown in Figure 2. Round off the measurement to the nearest centimeter. Record your hand span in a class chart on the chalkboard. 2. After all your classmates have recorded their hand spans in the class chart, transfer the results to Data Table 5. Your results will show the total number of hands having the same hand span. 3. Construct a line graph of the results on a sheet of graph paper. Label the x-axis Hand-span length (cm) and the y-axis Number of students. Hand span Figure 2
28 Changes Over Time Name Date Class Changes Over Time Laboratory Investigation Observations Data Table 1 Length (mm) (Group Data) Lima beans Leaf blades Petioles Data Table 2 Class Data for Lima Bean Lengths Length of lima bean (mm) Total number of beans of this size Data Table 3 Class Data for Leaf Blade Lengths Length of leaf blade (mm) Total number of leaf blades of this size Data Table 4 Class Data for Petiole Lengths Length of petiole (mm) Total number of petioles of this size Data Table 5 Class Data for Hand-Span Lengths Length of hand span (cm) Total number of hand spans of this size
29 Changes Over Time Laboratory Investigation Variation in a Population (continued) Analyze and Conclude 1. In what length range are most of the lima beans? Most of the leaf blades? Most of the petioles? 2. In what length range are the fewest beans? The fewest blades? The fewest petioles? 3. What is the general shape of the graphs of the lengths of the lima beans, leaf blades, and petioles? What does the shape of the graphs indicate about these lengths? 4. Which hand-span length occurs most often? Least often? 5. What is the general shape of the graph of hand spans? What does the shape of the graph indicate about the hand spans of students in your class? Critical Thinking and Applications 6. List two ways in which a large hand span might be a useful human adaptation. 7. Do you think having many seeds in a pod would be a more useful adaptation for a bean plant than having only a few seeds? Give a reason for your answer. 8. Why might having large leaves be a harmful characteristic for a desert plant? More to Explore Investigate variations that occur in the lengths of peanut shells. Make your measurements and graph the results as you did in the previous part of this lab. Do you think that all organisms of the same species show variation in all of their traits? Give a reason for your answer. CAUTION: Do not eat the peanuts.