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Teaching About Evolution and the Nature of Science 6 Activities for Teaching About Evolution and the Nature of Science Prior chapters in this volume answer the what and why questions of teaching about evolution and the nature of science. As every educator knows, such discussions only set a stage. The actual play occurs when science teachers act on the basic content and well-reasoned arguments for inclusion of evolution and the nature of science in school science programs. This chapter goes beyond discussions of content and rationales. It presents, as examples of investigative teaching exercises, eight activities that science teachers can use as they begin developing students' understandings and abilities of evolution and the nature of science. The following descriptions briefly introduce each activity. Activity 1: Introducing Inquiry and the Nature of Science This activity introduces basic procedures involved in inquiry and concepts describing the nature of science. In the first portion of the activity the teacher uses a numbered cube to involve students in asking a question—what is on the unseen bottom of the cube?—and the students propose an explanation based on their observations. Then the teacher presents the students with a second cube and asks them to use the available evidence to propose an explanation for what is on the bottom of this cube. Finally, students design a cube that they exchange and use for an evaluation. This activity provides students with opportunities to learn the abilities and understandings aligned with science as inquiry and the nature of science as described in the National Science Education Standards.1 Designed for grades 5 through 12, the activity requires a total of four class periods to complete. Lower grade levels might only complete the first cube and the evaluation where students design a problem based on the cube activity. Activity 2: The Formulation of Explanations: An Invitation to Inquiry on Natural Selection This activity uses the concept of natural selection to introduce the idea of formulating and testing a scientific hypothesis. Through a focused discussion approach, the teacher provides information and allows students time to think, interact with peers, and propose explanations for observations described by the teacher. The teacher then provides more information, and the students continue their discussion based on the new information. This activity will help students in grades 5 through 8 develop abilities related to scientific inquiry and formulate understandings about the nature of science. Activity 3: Investigating Natural Selection In this activity, the students investigate one mechanism for evolution through a simulation that models the principles of natural selection and helps answer the question: How might biological change have occurred and been reinforced over time? The activity is designed for grades 9 through 12 and requires three class periods. Activity 4: Investigating Common Descent: Formulating Explanations and Models In this activity, students formulate explanations and models that simulate structural and biochemical
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Teaching About Evolution and the Nature of Science data as they investigate the misconception that humans evolved from apes. The investigations require two 45-minute periods. They are designed for use in grades 9 through 12. Activity 5: Proposing Explanations for Fossil Footprints In this investigation, students observe and interpret "fossil footprint" evidence. From the evidence, they are asked to construct defensible hypotheses or explanations for events that took place in the geologic past. Estimated time requirements for this activity: two class periods. This activity is designed for grades 5 through 8. Activity 6: Understanding Earth's Changes Over Time Comparing the magnitude of geologic time to spans of time within a person's own lifetime is difficult for many students. In this activity, students use a long paper strip and a reasonable scale to represent visually all of geologic time, including significant events in the development of life on earth as well as recent human events. The investigation requires two class periods and is appropriate for grades 5 through 12. Activity 7: Proposing the Theory of Biological Evolution: Historical Perspective This activity uses historical perspectives and the theme of evolution to introduce students to the nature of science. The teacher has students read short excerpts of original statements on evolution from Jean Lamarck, Charles Darwin, and Alfred Russel Wallace. These activities are intended as either supplements to other investigations or core activities. Designed for grades 9 through 12, the activities should be used as part of three class periods. Activity 8: Connecting Population Growth and Biological Evolution In this activity, students develop a model of the mathematical nature of population growth. The investigation provides an excellent opportunity for consideration of population growth of plant and animal species and the relationship to mechanisms promoting natural selection. This activity will require two class periods and is appropriate for grades 5 through 12. The activities in this chapter do not represent a curriculum. They are directed, instead, toward other purposes. First, they present examples of standards-based instructional materials. In this case, the level of organization is an activity—one to five days of lessons—and not a larger level of organization such as a unit of several weeks, a semester, or a year. Also, these exercises generally do not use biological materials, such as fruit flies, or computer simulations. The use of these instructional materials in the curriculum greatly expands the range of possible investigations. Second, these activities demonstrate how existing exercises can be recast to emphasize the importance of inquiry and the fundamental concepts of evolution. Each of these exercises was derived from already existing activities that were revised to reflect the National Science Education Standards. For each exercise, student outcomes drawn from the Standards are listed to focus attention on the concepts and abilities that students are meant to develop. Third, the activities demonstrate some, but not all, of the criteria for curricula to be described in Chapter 7. For example, several of the activities emphasize inquiry and the nature of science while others focus on concepts related to evolution. All activities use an instructional model, described in the next section, that increases coherence and enhances learning. Finally, there remains a paucity of instructional materials for teaching evolution and the nature of science. Science teachers who recognize this need are encouraged to develop new materials and lessons to introduce the themes of evolution and the nature of science. (See http://www4.nas.edu/opus/evolve.nsf) Developing Students' Understanding and Abilities: The Curriculum Perspective For students to develop an understanding of evolution and the nature of science requires many years and a variety of educational experiences.
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Teaching About Evolution and the Nature of Science Teachers cannot rely on single lessons, chapters, or biology and earth science courses for students to integrate the ideas presented in this document into their own understanding. In early grades (K–4) students might learn the fundamental concepts associated with "characteristics of organisms," "life cycles," and "organisms and environments." In middle grades they learn more about ''reproduction and heredity" and "diversity and adaptation of organisms." Such learning experiences, as described in the National Science Education Standards, set a firm foundation for the study of biological evolution in grades 9–12. The slow and steady development of concepts such as evolution and related ideas such as natural selection and common descent requires careful consideration of the overall structure and sequence of learning experiences. Although this chapter does not propose a curriculum or a curriculum framework, current efforts by Project 2061 of the American Association for the Advancement of Science (AAAS) demonstrate the interrelated nature of students' understanding of science concepts and emphasize the importance of well-designed curricula at several levels of organization (for example, activities, units, and school science programs). The figure on the next page presents the "Growth-of-Understanding Map for Evolution and Natural Selection" based on Benchmarks for Science Literacy.2 Developing Student Understanding and Abilities: The Instructional Perspective The activities in the chapter incorporate an instructional model, summarized in the accompanying box, that includes five steps: engagement, exploration, explanation, elaboration, and evaluation. Just as scientific investigations originate with a question that engages a scientist, so too must students engage in the activities of learning. The activities therefore begin with a strategic question that gets students thinking about the content of the lesson. Once engaged, students need time to explore ideas before concepts begin to make sense. In this exploration phase, students try their ideas, ask questions, and look for possible answers to questions. Students use inquiry strategies; they try to An Instructional Model ENGAGE This phase of the instructional model initiates the learning task. The activity should (1) make connections between past and present learning experiences and (2) anticipate activities and focus students' thinking on the learning outcomes of current activities. Students should become mentally engaged in the concept, process, or skill to be explored. EXPLORE This phase of the teaching model provides students with a common base of experiences within which they identify and develop current concepts, processes, and skills. During this phase,xxxxx students actively explore their environment or manipulate materials. EXPLAIN This phase of the instructional model focuses students' attention on a particular aspect of their engagement and exploration experiences and provides opportunities for them to develop explanations and hypotheses. This phase also provides opportunities for teachers to introduce a formal label or definition for a concept, process, skill, or behavior. ELABORATE This phase of the teaching model challenges and extends students' conceptual understanding and allows further opportunity for students to test hypotheses and practice desired skills and behaviors. Through new experiences, the students develop a deeper and broader understanding, acquire more information, and develop and refine skills. EVALUATE This phase of the teaching model encourages students to assess their understanding and abilities and provides opportunities for teachers to evaluate student progress toward achieving the educational objectives.
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Teaching About Evolution and the Nature of Science
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Teaching About Evolution and the Nature of Science relate their ideas to those of other students and to what scientists already know about evolution. In the third step, students can propose answers and develop hypotheses. Also in this step, the teacher explains what scientists know about the questions. This is the step when teachers should make the major concepts explicit and clear to the students. Educators understand that informing students about a concept does not necessarily result in their immediate comprehension and understanding of the idea. These activities therefore provide a step referred to as elaboration in which students have opportunities to apply their ideas in new and slightly different situations. Finally, how well do students understand the concepts, or how successful are they at applying the desired skills? These are the questions to be answered during the evaluation phase. Ideally, evaluations are more than tests. Students should have opportunities to see if their ideas can be applied in new situations and to compare their understanding with scientific explanations of the same phenomena.
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Teaching About Evolution and the Nature of Science Activity 1 Introducing Inquiry and the Nature of Science This activity introduces basic procedures involved in inquiry and concepts describing the nature of science. In the first portion of the activity the teacher uses a numbered cube to involve students in asking a question—what is on the bottom?— and the students propose an explanation based on their observations. Then the teacher presents the students with a second cube and asks them to use the available evidence to propose an explanation for what is on the bottom of this cube. Finally, students design a cube that they exchange and use for an evaluation. This activity provides students with opportunities to learn the abilities and understandings aligned with science as inquiry and the nature of science as described in the National Science Education Standards. Designed for grades 5 through 12, the activity requires a total of four class periods to complete. Lower grade levels might only complete the first cube and the evaluation where students design a problem based on the cube activity. Standards-Based Outcomes This activity provides all students with opportunities to develop abilities of scientific inquiry as described in the National Science Education Standards. Specifically, it enables them to: identify questions that can be answered through scientific investigations, design and conduct a scientific investigation, use appropriate tools and techniques to gather, analyze, and interpret data, develop descriptions, explanations, predictions, and models using evidence, think critically and logically to make relationship between evidence and explanations, recognize and analyze alternative explanations and predictions, and communicate scientific procedures and explanations. This activity also provides all students opportunities to develop understanding about inquiry and the nature of science as described in the National Science Education Standards. Specifically, it introduces the following concepts: Different kinds of questions suggest different kinds of scientific investigations. Current scientific knowledge and understanding guide scientific investigations. Technology used to gather data enhances accuracy and allows scientists to analyze and quantify results of investigations. Scientific explanations emphasize evidence, have logically consistent arguments, and use scientific principles, models, and theories. Science distinguishes itself from other ways of knowing and from other bodies of knowledge through the use of empirical standards, logical arguments, and skepticism, as scientists strive for the best possible explanations about the natural world. Science Background for Teachers The pursuit of scientific explanations often begins with a question about a natural phenomenon. Science is a way of developing answers, or improving explanations, for observations or events in the natural world. The scientific question can emerge from a child's curiosity about where the dinosaurs went or why the sky is blue. Or the question can extend scientists' inquiries into the process of extinction or the chemistry of ozone depletion. Once the question is asked, a process of scientific inquiry begins, and there eventually may be an answer or a proposed explanation. Critical aspects of science include curiosity and the freedom to pursue that curiosity. Other attitudes and habits of mind that characterize scientific inquiry and the activities of scientists include intelligence, honesty, skepticism, tolerance for ambiguity, openness to
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Teaching About Evolution and the Nature of Science new knowledge, and the willingness to share knowledge publicly. Scientific inquiry includes systematic approaches to observing, collecting information, identifying significant variables, formulating and testing hypotheses, and taking precise, accurate, and reliable measurements. Understanding and designing experiments are also part of the inquiry process. Scientific explanations are more than the results of collecting and organizing data. Scientists also engage in important processes such as constructing laws, elaborating models, and developing hypotheses based on data. These processes extend, clarify, and unite the observations and data and, very importantly, develop deeper and broader explanations. Examples include the taxonomy of organisms, the periodic table of the elements, and theories of common descent and natural selection. One characteristic of science is that many explanations continually change. Two types of changes occur in scientific explanations: new explanations are developed, and old explanations are modified. Just because someone asks a question about an object, organism, or event in nature does not necessarily mean that person is pursuing a scientific explanation. Among the conditions that must be met to make explanations scientific are the following: Scientific explanations are based on empirical observations or experiments. The appeal to authority as a valid explanation does not meet the requirements of science. Observations are based on sense experiences or on an extension of the senses through technology. Scientific explanations are made public. Scientists make presentations at scientific meetings or publish in professional journals, making knowledge public and available to other scientists. Scientific explanations are tentative. Explanations can and do change. There are no scientific truths in an absolute sense. Scientific explanations are historical. Past explanations are the basis for contemporary explanations, and those, in turn, are the basis for future explanations. Scientific explanations are probabilistic. The statistical view of nature is evident implicitly or explicitly when stating scientific predictions of phenomena or explaining the likelihood of events in actual situations. Scientific explanations assume cause-effect relationships. Much of science is directed toward determining causal relationships and developing explanations for interactions and linkages between objects, organisms, and events. Distinctions among causality, correlation, coincidence, and contingency separate science from pseudoscience. Scientific explanations are limited. Scientific explanations sometimes are limited by technology, for example, the resolving power of microscopes and telescopes. New technologies can result in new fields of inquiry or extend current areas of study. The interactions between technology and advances in molecular biology and the role of technology in planetary explorations serve as examples. Science cannot answer all questions. Some questions are simply beyond the parameters of science. Many questions involving the meaning of life, ethics, and theology are examples of questions that science cannot answer. Refer to the National Science Education Standards for Science as Inquiry (pages 145-148 for grades 5-8 and pages 175-176 for grades 9-12), History and Nature of Science Standards (pages 170-171 for grades 5-8 and pages 200-204 for grades 9-12), and Unifying Concepts and Processes (pages 116-118). Chapter 3 of this document also contains a discussion of the nature of science. Materials and Equipment 1 cube for each group of four students (black-line masters are provided). (Note: you may wish to complete the first portion of the activity as a demonstration for the class. If so, construct one large cube using a cardboard box. The sides should have the same numbers and markings as the black-line master.) 10 small probes such as tongue depressors or pencils. 10 small pocket mirrors. Instructional Strategy Engage Begin by asking the class to tell you what they know about how scientists do their work. How would they describe a scientific investigation? Get students thinking about the process of scientific
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Teaching About Evolution and the Nature of Science inquiry and the nature of science. This is also an opportunity for you to assess their current understanding of science. Accept student answers and record key ideas on the overhead or chalkboard. Explore (The first cube activity can be done as a demonstration if you construct a large cube and place it in the center of the room.) First, have the students form groups of three or four. Place the cubes in the center of the table where the students are working. The students should not touch, turn, lift, or open the cube. Tell the students they have to identify a question associated with the cube. Allow the students to state their questions. Likely questions include: What is in the cube? What is on the bottom of the cube? What number is on the bottom? You should direct students to the general question, what is on the bottom of the cube? Tell the students that they will have to answer the question by proposing an explanation, and that they will have to convince you and other students that their answer is based on evidence. (Evidence refers to observations the group can make about the visible sides of the cube.) Allow the students time to explore the cube and to develop answers to their question. Some observations or statements of fact that the students may make include: The cube has six sides. The cube has five exposed sides. The numbers and dots are black. The exposed sides have numbers 1, 3, 4, 5, and 6. The opposite sides add up to seven. The even-numbered sides are shaded. The odd-numbered sides are white. Ask the students to use their observations (the data) to propose an answer to the question: What is on the bottom of the cube? The student groups should be able to make a statement such as: We conclude there is a 2 on the bottom. Students should present their reasoning for this conclusion. For example, they might base their conclusion on the observation that the exposed sides are 1, 3, 4, 5, and 6, and because 2 is missing from the sequence, they conclude it is on the bottom. Use this opportunity to have the students develop the idea that combining two different but logically related observations creates a stronger explanation. For example, 2 is missing in the sequence (that is, 1, _, 3, 4, 5, 6) and that opposite sides add up to 7 (that is, 1–6; 3–4; _–5) and because 5 is on top, and 5 and 2 equal 7, 2 could be on the bottom. If done as a demonstration, you might put the cube away without showing the bottom or allowing students to dismantle it. Explain that scientists often are uncertain about their proposed answers, and often have no way of knowing the absolute answer to a scientific question. Examples such as the exact ages of stars and the reasons for the extinction of prehistoric organisms will support the point. Explain Begin the class period with an explanation of how the activity simulates scientific inquiry and provides a model for science. Structure the discussion so students make the connections between their experiences with the cube and the key points (understandings) you wish to develop. Key points from the Standards include the following: Science originates in questions about the world. Science uses observations to construct explanations (answers to the questions). The more observations you had that supported your proposed explanation, the stronger your explanation, even if you could not confirm the answer by examining the bottom of the cube. Scientists make their explanations public through presentations at professional meetings and journals. Scientists present their explanations and critique the explanations proposed by other scientists. The activity does not explicitly describe "the scientific method." The students had to work to answer the question and probably did it in a less than systematic way. Identifiable elements of a method—such as observation, data, and hypotheses—were clear but not applied systematically. You can use the experiences to point out and clarify scientific uses of terms such as observation, hypotheses, and data.
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Teaching About Evolution and the Nature of Science For the remainder of the second class period you should introduce the "story" of an actual scientific discovery. Historic examples such as Charles Darwin would be ideal. You could also assign students to prepare brief reports that they present. Elaborate The main purpose of the second cube is to extend the concepts and skills introduced in the earlier activities and to introduce the role of prediction, experiment, and the use of technology in scientific inquiry. The problem is the same as the first cube: What is on the bottom of the cube? Divide the class into groups of three and instruct them to make observations and propose an answer about the bottom of the cube. Student groups should record their factual statements about the second cube. Let students identify and organize their observations. If the students are becoming too frustrated, provide helpful suggestions. Essential data from the cube include the following (see black-line master): Names and numbers are in black. Exposed sides have either a male or female name. Opposing sides have a male name on one side and a female name on the other. Names on opposite sides begin with the same letters. The number in the upper-right corner of each side corresponds to the number of letters in the name on that side. The number in the lower-left corner of each side corresponds to the number of the first letter that the names on opposite sides have in common. The number of letters in the names on the five exposed sides progresses from three (Rob) to seven (Roberta). Four names, all female, could be on the bottom of the cube: Fran, Frances, Francene, and Francine. Because there are no data to show the exact name, groups might have different hypotheses. Tell the student groups that scientists use patterns in data to make predictions and then design an experiment to assess the accuracy of their prediction. This process also produces new data. Tell groups to use their observations (the data) to make a prediction of the number in the upper-right corner of the bottom. The predictions will most likely be 4, 7, or 8. Have the team decide which corner of the bottom they wish to inspect and why they wish to inspect it. The students might find it difficult to determine which corner they should inspect. Let them struggle with this and even make a mistake—this is part of science! Have one student obtain a utensil, such as a tweezers, probe, or tongue depressor, and a mirror. The student may lift the designated corner less than one inch and use the mirror to look under the corner. This simulates the use of technology in a scientific investigation. The groups should describe the data they gained by the "experiment." Note that the students used technology to expand their observations and understanding about the cube, even if they did not identify the corner that revealed the most productive evidence. If students observe the corner with the most productive information, they will discover an 8 on the bottom. This observation will confirm or refute the students' working hypotheses. Francine or Francene are the two possible names on the bottom. The students propose their answer to the question and design another experiment to answer the question. Put the cube away without revealing the bottom. Have each of the student groups present brief reports on their investigation. Evaluate The final cube is an evaluation. There are two parts to the evaluation. First, in groups of three, students must create a cube that will be used as the evaluation exercise for other groups. After a class period to develop a cube, the student groups should exchange cubes. The groups should address the same question: What is on the bottom of the cube? They should follow the same rules—for example, they cannot pick up the cube. The groups should prepare a written report on the cube developed by their peers. (You may have the students present oral reports using the same format.) The report should include the following: title, the question they pursued, observation—data, experiment—new data,
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Teaching About Evolution and the Nature of Science proposed answer and supporting data, a diagram of the bottom of the cube, and suggested additional experiments. Due to the multiple sources of data (information), this cube may be difficult for students. It may take more than one class period, and you may have to provide resources or help with some information. Remember that this activity is an evaluation. You may give some helpful hints, especially for information, but since the evaluation is for inquiry and the nature of science you should limit the information you provide on those topics. Student groups should complete and hand in their reports. If student groups cannot agree, you may wish to make provisions for individual or "minority reports." You may wish to have groups present oral reports (a scientific conference). You have two opportunities to evaluate students on this activity: you can evaluate their understanding of inquiry and the nature of science as they design a cube, and you can assess their abilities and understandings as they figure out the unknown cube.
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Teaching About Evolution and the Nature of Science
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Teaching About Evolution and the Nature of Science centered on the study of nature and collecting a diversity of organisms. After graduation, Darwin's professor recommended him for the position of naturalist on H.M.S. Beagle. The voyage of the Beagle lasted five years (1831 to 1836) and provided the observations and evidence (in the form of specimens) that became the foundation for Darwin's theories. Of particular note in history is Darwin's observations on the Galapagos Islands located off the coast of Ecuador. Darwin's curiosity and insight led him to observe both similarities and differences among organisms and compare them on the mainland and the islands 600 miles offshore. Based on his observations, he wondered about the origin of different plants and animals, and the variations in species he recorded in similar organisms. After returning to England, Darwin spent more than twenty years studying the specimens, experimenting, and reviewing the notes of his voyage. In 1858 he was surprised to find that Alfred Russel Wallace had formulated similar conclusions. In the same year, Darwin reported his and Wallace's work in a joint presentation to the Scientific Society in London. One year later, in 1859, Darwin published On the Origin of Species by Means of Natural Selection. This publication caused great debate and what is now viewed as a scientific revolution. Darwin's theories of evolution have also had considerable impact on society and our cultural views. Alfred Russel Wallace (1823 to 1913) was also born in England. He became a teacher of English. He later developed an interest in collecting plants and insects. In 1848 he made an expedition to the Amazon River in Brazil to collect scientific materials. On a later expedition to the Malay Islands, Wallace observed some variations in organisms that engaged the same questions that Darwin posed—why did each island have different species? Wallace thought about the question for three years and in 1858 he proposed his theory. Materials and Equipment Excerpt from Zoological Philosophy by Jean Lamarck (provided) Excerpt from On the Tendency of Varieties to Depart Indefinitely from the Original Type by Alfred Russel Wallace (provided) Excerpt from On the Origin of Species by Charles Darwin (provided) Instructional Strategy These excerpts give the students an opportunity to read original statements by individuals who contributed to a major revolution in the history of biology. The instructional strategy is that of small-group discussions. Students read an original excerpt prior to class and discuss the reading in class. Engage Introduce the sequence of readings by asking questions based on the learning outcomes: How do you think the society in which scientists live might influence their views? What makes a person's explanation scientific? Can scientific explanations change? If so, how? Why? If not, why not? Can you name some major theories in science? In biology? Ask the students what they know about the theory of evolution. What do they know about Charles Darwin? When did he propose his theory? Did any other individuals propose theories about evolution? How did Darwin develop his theory of evolution? Questions such as these will set the stage for the first reading. Assign the reading by Jean Lamarck as homework. Explore Students should work in groups of four to discuss Jean Lamarck's explanations of changes in organisms. Questions for student discussions include: What is the role of the environment in Lamarck's explanation? What scientific approach is suggested by Lamarck's statement: "Nothing of all this can be considered as hypothesis or private opinion; on the contrary, they are truths which, in order to be made clear, only require attention and the observation of facts." Was Lamarck's explanation scientific? Why or why not? Can you propose any other explanations for Lamarck's observations about the disuse and use of organs? Explain Prior to this group discussion, assign the reading by Alfred Russel Wallace. With your guidance, this discussion should clarify for students
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Teaching About Evolution and the Nature of Science some of the fundamental concepts about science as a human endeavor and the nature of science. This should include discussion in groups of four followed by a full class summary of the learning outcomes. How would you characterize Wallace's idea that "The life of wild animals is a struggle for existence?" How is Wallace's view scientific? Wallace claims that "useful variations will tend to increase, unuseful or hurtful variations to diminish." How does this occur? What evidence does he cite? How does Wallace's explanation differ from Lamarck's? What do you think of Wallace's critique of Lamarck's hypotheses? Elaborate Prior to this group discussion, assign the reading by Charles Darwin. In these discussions, students should apply concepts about the nature of science and the historical perspective developed during prior discussions. This discussion should demonstrate greater sophistication and understanding by the students. What led Darwin to formulate his ideas about the origin of species? On what did he base his explanations? What did Darwin propose as the origin of species? What was the relationship of Lamarck's and Wallace's work to Darwin's? Was Darwin's explanation scientific? Why or why not? How did Darwin attempt to determine how modifications of a species are accomplished? How did Darwin explain the incomplete nature of his ideas? Evaluate Have each student write a brief essay on the nature of scientific knowledge as demonstrated in the development of the theory of evolution. They should cite at least two quotes from the reading to support their discussion. The essays should incorporate the concepts of adaptation, natural selection, and descent from common ancestors.
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Teaching About Evolution and the Nature of Science Student Sheet Zoological Philosophy Jean Lamarck (1809) The environment affects the shape and organization of animals, that is to say that when the environment becomes very different, it produces in course of time corresponding modifications in the shape and organization of animals. If a new environment, which has become permanent for some race of animals, induces new habits in these animals, that is to say, leads them into new activities which become habitual, the result will be the use of some one part in preference to some other part, and in some cases the total disuse of some part no longer necessary. Nothing of all this can be considered as hypothesis or private opinion; on the contrary, they are truths which, in order to be made clear, only require attention and the observation of facts. Snakes have adopted the habit of crawling on the ground and hiding in the grass; so that their body, as a result of continually repeated efforts at elongation for the purpose of passing through narrow spaces, has acquired a considerable length, quite out of proportion to its size. Now, legs would have been quite useless to these animals and consequently unused. Long legs would have interfered with their need of crawling, and very short legs would have been incapable of moving their body, since they could only have had four. The disuse of these parts thus became permanent in the various races of these animals, and resulted in the complete disappearance of these same parts, although legs really belong to the plan or organization of the animals of this class. The frequent use of any organ, when confirmed by habit, increases the functions of that organ, leads to its development, and endows it with a size and power that it does not possess in animals which exercise it less. We have seen that the disuse of any organ modifies, reduces, and finally extinguishes it. I shall now prove that the constant use of any organ, accompanied by efforts to get the most out of it, strengthens and enlarges that organ, or creates new ones to carry on the functions that have become necessary. The bird which is drawn to the water by its need of finding there the prey on which it lives, separates the digits of its feet in trying to strike the water and move about on the surface. The skin which unites these digits at their base acquires the habit of being stretched by these continually repeated separations of the digits; thus in course of time there are formed large webs which unite the digits of ducks, geese, etc. as we actually find them. It is interesting to observe the result of habit in the peculiar shape and size of the giraffe; this animal, the largest of the mammals, is known to live in the interior of Africa in places where the soil is nearly always arid and barren, so that it is obliged to browse on the leaves of trees and to make constant efforts to reach them. From this habit long maintained in all its race, it has resulted that the animal's fore-legs have become longer than its hind legs, and that its neck is lengthened to such a degree that the giraffe, without standing up on its hind legs, attains a height of six metres (nearly twenty feet). Philosophie Zoologique. Paris. 1809. Translated by H. Elliott, Macmillan Company, London. 1914.
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Teaching About Evolution and the Nature of Science Student Sheet On the Tendency of Varieties to Depart Indefinitely from the Original Type Alfred Russel Wallace (1858) The Struggle for Existence The life of wild animals is a struggle for existence. The full exertion of all their faculties and all their energies is required to preserve their own existence and provide for that of their infant offspring. The possibility of procuring food during the least favorable seasons and of escaping the attacks of their most dangerous enemies are the primary conditions which determine the existence both of individuals and of entire species. The numbers that die annually must be immense; and as the individual existence of each animal depends upon itself, those that die must be the weakest—the very young, the aged, and the diseased—while those that prolong their existence can only be the most perfect in health and vigor, those who are best able to obtain food regularly and avoid their numerous enemies. It is ''a struggle for existence," in which the weakest and least perfectly organized must always succumb. Useful Variations Will Tend to Increase, Unuseful or Hurtful Variations to Diminish Most or perhaps all the variations from the typical form of a species must have some definite effect, however slight, on the habits or capacities of the individuals. Even a change of color might, by rendering them more or less distinguishable, affect their safety; a greater or less development of hair might modify their habits. More important changes, such as an increase in the power or dimensions of the limbs or any of the external organs, would more or less affect their mode of procuring food or the range of country which they could inhabit. It is also evident that most changes would affect, either favorable or adversely, the powers of prolonging existence. An antelope with shorter or weaker legs must necessarily suffer more from the attacks of the feline carnivora; the passenger pigeon with less powerful wings would sooner or later be affected in its powers of procuring a regular supply of food; and in both cases the result must necessarily be a diminution of the population of the modified species. If, on the other hand, any species should produce a variety having slightly increased powers of preserving existence, that variety must inevitably in time acquire a superiority in numbers. Lamarck's Hypothesis Very Different from that Now Advanced The hypothesis of Lamarck—that progressive changes in species have been produced by the attempts of animals to increase the development of their own organs and thus modify their structure and habits—has been repeatedly and easily refuted by all writers on the subject of varieties and species. The giraffe did not acquire its long neck by desiring to reach the foliage of the more lofty shrubs and constantly stretching its neck for the purpose, but because any varieties which occurred among its ancestors with a longer neck than usual at once secured a fresh range of pasture over the same ground as their shorter-necked companions, and on the first scarcity of food were thereby enabled to outlive them. Journal of the Proceedings of the Linnean Society August 1858, London
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Teaching About Evolution and the Nature of Science Student Sheet On the Origin of Species Charles Darwin (1859) Introduction When on board H.M.S. Beagle, as naturalist, I was much struck with certain facts in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to me to throw some light on the origin of species—that mystery of mysteries, as it has been called by one of our greatest philosophers. On my return home, it occurred to me, in 1837, that something might perhaps be made out on this question by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing on it. After five years work I allowed myself to speculate on the subject, and drew up some short notes; these I enlarged in 1844 into a sketch of the conclusions, which then seemed to me probable; from that period to the present day I have steadily pursued the same object. I hope that I may be excused for entering on these personal details, as I give them to show that I have not been hasty in coming to a decision. My work is now nearly finished; but as it will take me two or three more years to complete it, and as my health is far from strong, I have been urged to publish this Abstract. I have more especially been induced to do this, as Mr. Wallace, who is now studying the natural history of the Malay archipelago, has arrived at almost exactly the same general conclusions that I have on the origin of species. Last year he sent to me a memoir on this subject, with a request that I would forward it to Sir Charles Lyell, who sent it to the Linnean Society, and it is published in the third volume of the Journal of that Society. Sir C. Lyell and Dr. Hooker, who both knew of my work—the latter having read my sketch of 1844—honoured me by thinking it advisable to publish, with Mr. Wallace's excellent memoir, some brief extracts from my manuscripts. In considering the Origin of Species, it is quite conceivable that a naturalist, reflecting on the mutual affinities of organic beings, on their embryological relations, their geographical distribution, geological succession, and other such facts, might come to the conclusion that each species had not been independently created, but had descended, like varieties, from other species. Nevertheless, such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the innumerable species inhabiting this world have been modified, so as to acquire that perfection of structure and coadaptation which most justly excites our admiration. Naturalists continually refer to external conditions, such as climate, food, etc., as the only possible cause of variation. In one very limited sense, as we shall hereafter see, this may be true; but it is preposterous to attribute to mere external conditions, the structure, for instance, of the woodpecker, with its feet, tail, beak, and tongue, so admirable adapted to catch insects under the bark of trees. In the case of the misseltoe, which draws its nourishment from certain trees, which has seeds that must be transported by certain birds, and which has flowers with separate sexes absolutely requiring the agency of certain insects to bring pollen from one flower to the other, it is equally preposterous to account for the structure of this parasite, with its relations to several distinct organic beings, by the effects of external conditions, or of habit, or of the volition of the plant itself. The author of the 'Vestiges of Creation' would, I presume, say that, after a certain unknown number of generations, some bird had given birth to a woodpecker, and some plant to the misseltoe, and that these had been produced perfect as we
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Teaching About Evolution and the Nature of Science Student Sheet now see them; but this assumption seems to me to be no explanation, for it leaves the case of the coadaptations of organic beings to each other and to their physical condition of life, untouched and unexplained. It is, therefore, of the highest importance to gain a clear insight into the means of modification and coadaptation. At the commencement of my observations it seemed to me probable that a careful study of domesticated animals and of cultivated plants would offer the best chance of making out this obscure problem. Nor have I been disappointed; in this and in all other perplexing cases I have invariable found that our knowledge, imperfect though it be, of variation under domestication, afforded the best and safest clue. I may venture to express my conviction of the high value of such studies, although they have been very commonly neglected by naturalists. No one ought to feel surprise at much remaining as yet unexplained in regard to the origin of species and varieties, if he makes due allowance for our profound ignorance in regard to the mutual relations of all the beings which live around us. Who can explain why one species ranges widely and is very numerous, and why another allied species has a narrow range and is rare? Yet these relations are of the highest importance, for they determine the present welfare, and, as I believe, the future success and modification of every inhabitant of this world. Still less do we know of the mutual relations of the innumerable inhabitants of the world during the many past geological epochs in its history. Although much remains obscure, and will long remain obscure, I can entertain no doubt, after the most deliberate study and dispassionate judgment of which I am capable, that the view which most naturalists entertain, and which I formerly entertained—namely, that each species has been independently created—is erroneous. I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendants of that species. Furthermore, I am convinced that Natural Selection has been the main but not exclusive means of modification. On the Origin of Species by Means of Natural Selection. London. 1859.
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Teaching About Evolution and the Nature of Science Activity 8 Connecting Population Growth and Biological Evolution In this activity, students develop a model of the mathematical nature of population growth. The investigation provides an excellent opportunity for consideration of the population growth of plant and animal species and the resultant stresses that contribute to natural selection. This activity will require two class periods and is appropriate for grades 5 through 12. The activity is based on an original activity from the Earth Science Curriculum Project. It is used with permission.14 Standards-Based Outcomes This activity provides all students an opportunity to develop understandings about scientific inquiry and biological evolution as described in the National Science Education Standards. Specifically, it conveys the following concepts: Mathematics is essential in scientific inquiry. Mathematical tools and models guide and improve the posing of questions, gathering data, constructing explanations, and communicating results. Species evolve over time. Evolution is the consequence of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuing selection of those offspring better able to survive and leave offspring in a particular environment. (Item 1 is the primary content emphasis of this activity. Teachers can introduce the other factors as appropriate.) Populations grow or decline through the combined effects of births and deaths and through emigration and immigration into specific areas. Populations can increase through linear or exponential growth, with effects on resource use and on environmental pollution. Populations can reach limits to growth. Carrying capacity is the maximum number of organisms that can be supported by a given environment. Living organisms have the capacity to produce populations of arbitrarily large size, but environments and resources are finite. This fundamental tension has profound effects on the interactions between organisms. Science Background for Teachers The tension between expanding populations and limited resources was a fundamental point that Darwin came to understand when he read Thomas Malthus.15 This understanding subsequently had an important influence on the formulation of his theory of natural selection. This activity extends the general idea of population growth to humans. Here the important point is that human beings live within the world's ecosystems. Increasingly, humans modify ecosystems as a result of population growth, technology, and consumption. Human destruction of habitats through direct harvesting, pollution, atmospheric changes, and other factors is threatening current global stability, and, if not addressed, ecosystems will be irreversibly affected. The increase in the size of a population (such as the human population) is an example of exponential growth. The human population grew at the slow rate of only about 0.002 percent a year for the first several million years of our existence. Since then the average annual rate of human population has increased to an all-time high of 2.06 percent in 1970. As the base number of people undergoing growth has increased, it has taken less and less time to add each new billion people. It took 2 million years to add the first billion people; 130 years to add the second billion; 30 years to add the third billion; 15 years to add the fourth billion; and only 12 years to add the fifth billion. We are now approaching the sixth billion. Materials and Equipment Each group of three or four students will need:
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Teaching About Evolution and the Nature of Science Approximately 2,000 small, uniformly shaped objects (kernels of corn, dried beans, wooden markers, plastic beads) 10 paper cups or small beakers A 250-ml or 400-ml beaker Instructional Strategy Engage Initiate a discussion on human population with such questions as: How long have humans been on the earth? How do you think the early rate of human population growth compares with the population growth rate today? Why did this rate change? Tell students that this investigation represents a model of population growth rates. Explore Have student groups complete the following activities. Place the glass beakers on their desks. Begin by placing two objects (e.g., corn or plastic beads) in it. The beaker represents the limits of an ecosystem or ultimately the earth. Place 10 cups in a row on their desk. In the first cup, place two objects. In the second cup, place twice as many objects as the first cup (four). Have students record the number of objects on the outside of the cup. Continue this procedure by placing twice as many objects as in the former cup, or doubling the number, in cups 3 through 10. Be sure students record the numbers on the cups. Take the beaker and determine its height. Have students indicate the approximate percentage of volume that is without objects. Record this on the table as 0 time. At timed intervals of 30 seconds, add the contents of cups 1 through 10. Students should record the total population and approximate percentage of volume in the beaker that is without objects. Students should complete the procedure and graph their results as total population versus results. Students may question the need for the 30-second intervals. The length of the time interval is arbitrary. Any time interval will do. Preparation of the graph can be assigned as homework. Range of Results The mathematics involved in answering the questions may challenge some students. Assist students when necessary to enable them to accomplish the objectives of the investigation. Table 1 shows the population and the percent of the beaker's volume without objects. A typical student graph is shown in Figure 1. Explain Ask the students to explain the relationship between population growth and biological evolution in populations of microorganisms, plants, and animals. Through questions and discussion, help them develop the connections stated in the learning outcome for the activity. Evolution results from an interaction of factors related to the potential for species to increase in numbers, the genetic variability in a population, the supply of essential resources, and environmental pressures for selection of those offspring that are able to survive and reproduce. Elaborate Begin by having students explain the results of their activity. During the discussion of the graph, have the students consider some of the following: Are there any limitations to the number of people the earth will support? Which factor might limit population growth first? How does this factor relate to human evolution? Are Table 1 Population growth Time Internal Population Percentage of empty volume (400-ml beaker) 0 2 99% 1 4 99% 2 8 99% 3 16 98% 4 32 97% 5 64 95% 6 128 93% 7 256 88% 8 512 80% 9 1024 70% 10 2048 50% 11 4096 0%
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Teaching About Evolution and the Nature of Science Figure 1 Sample population growth graph there areas in the world where these limits have been reached already? Have we gone beyond the earth's ideal population yet? What problems will we face if we overpopulate the earth? How might human influence on, for example, habitats affect biological evolution. Students' answers to these questions will vary, depending on their background and information. The outcome, however, should be an intense discussion of some vital problems and should provide opportunities to introduce the fundamental concepts from the National Science Education Standards. Evaluation Human population on the earth is thought to have had a slow start, with doubling periods as long as 1 million years. The current world population is thought to be doubling every 37 years. How would this growth rate compare with the rates found in your investigation? Both the population in the investigation and on the earth increase in a geometric progression. This means the graphs have the same shape. You can substitute 37 years for every 30-second interval and the numbers will represent actual world population growth. The slope of the graph would remain the same. What happens to populations when they reach the limits to growth? The populations stop growing because death rates (or emigration) exceed birth rates (or immigration).
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Teaching About Evolution and the Nature of Science NOTES 1. National Research Council. 1996. National Science Education Standards. Washington, DC: National Academy Press. www.nap.edu/readingroom/books/nses 2. A Draft Growth-of-Understanding Map derived from Benchmarks for Science Literacy (Jan. 1998), AAAS (American Association for the Advancement of Science) Project 2061. 3. Biological Sciences Curriculum Study (BSCS). 1978. Biology Teachers' Handbook. 3rd ed. William V. Mayer, ed. New York: John Wiley and Sons, pp. 350-352. 4. Standards, p. 117. 5. Jonathan Weiner. 1994. The Beak of the Finch: A Story of Evolution in Our Time. New York: Alfred A. Knopf. 6. Tijs Goldschmidt. 1996. Darwin's Dreampond: Drama in Lake Victoria. Cambridge, MA: MIT Press. 7. BSCS Biology: A Human Approach. 1997. Dubuque, IA: Kendall/Hunt Publishing Co., pp. 47-49 and pp. 64-69. 8. See Chapter 2 of this document for more discussion on genetic variation and natural selection, and pages 158 and 185 of the National Science Education Standards. 9. Evolution: Inquiries into Biology and Earth Science by BSCS. 1992. Seattle: Videodiscovery, pp. 49-53 and pp. 211-221. 10. Standards, p. 117. 11. Earth Science Curriculum Project (ESCP). 1973. Investigating the Earth. rev. ed. Boston, MA: Houghton Mifflin. 12. Please review pages 143-148 of the National Science Education Standards. 13. Investigating the Earth. 14. Investigating the Earth. 15. Thomas Malthus. 1993. Essay on the Principle of Population. Geoffrey Gilbert, ed. Oxford: Oxford University Press.
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Teaching About Evolution and the Nature of Science
Representative terms from entire chapter: