To introduce the concept of evolution by natural selection from a historical standpoint and to examine the evidence and arguments that support this theory.
Science never takes places in a void and evolutionary thought is no exception. Although Charles Darwin is considered to be by many the "father" of evolutionary thought, he was in fact aided and guided by the works of many scientists before him. The theories and ideas proposed by his predecessors were limited to the information available at the time. Darwin himself had no knowledge of genetics and therefore, his theory of natural selection as an explanation of evolution was based solely on what he observed and knew at the time.
Because of the complexity of the evidence and the arguments that must be explained, a clear understanding of species evolution probably cannot be achieved earlier than high school. However, students in earlier grades (6-8) should have developed the evidence base for which the theory attempts to account. This lesson provides high-school students with an introduction to a more detailed study of evolution by focusing on the historical origins of Darwin's theory and the ideas that came before it. This historical study provides a good opportunity to feature the importance in science of careful observation and description and to illustrate that not all scientific advances depend on experimentation.
The goal of this lesson is for students to have the opportunity to examine how evolution has been scientifically explained historically. In doing so, students will examine the arguments and theories set forth by three historically important scientists: Jean Baptiste Lamarck, Alfred Russel Wallace, and Charles Darwin.
Information about Lamarck is found in most standard biology textbooks. Usually, there will be a brief description of his ideas and then a paragraph or two explaining why he was wrong. Often, students think that models that are no longer accepted must have been poorly developed. Students are also often unaware that Wallace independently developed the theory of natural selection to explain biological evolution. However, due to publishing dates, he is not given the same credit as Charles Darwin. Thus, students should not come away from this lesson thinking that Lamarck and Wallace were inferior scientists because the former's theory was incomplete and the latter did not receive public acclaim. The writings of both of these men made important contributions to evolutionary biology. Discussing these models provides a forum for talking about how and why scientific ideas change over time.
Research shows that students have a tendency to think in Lamarckian terms. That is, students often invoke the needs of organisms when accounting for change over time (Bishop and Anderson, 1990). They may also often believe that evolution is goal-directed. Discussion of Lamarck's ideas will provide a context in which a clear distinction can be made between these ideas and those of Darwin. The purpose of this lesson, however, is not to begin to make comparisons, but simply to make certain students understand how arguments have changed over time. By understanding the arguments put forth by Lamarck and Darwin, students can make fruitful comparisons in another Science NetLinks lesson, Comparing Theories: Lamarck and Darwin.
Using the History of Evolutionary Theory student esheet, students should visit Pre-Darwinian Theories for an explanation of the development of modern evolutionary thinking. Students should read the page on Pre-Darwinian Theories and then move on to Darwin and Natural Selection by clicking on "Next Topic" at the bottom of the page. After students have completed the reading, ask them these questions, which are meant to assess students' preconceptions and ideas about evolution, the theory of natural selection, and Darwin's role in history.
- What is this reading about?
- How do you think society influences a scientist's view?
- How do you think religion influences a scientist's view?
- How can scientific explanations change over time?
- What is evolution?
(Students may not know the distinction between evolution, the historical changes in life forms that are well substantiated and generally accepted as fact by scientists, and natural selection, the proposed mechanism for these changes. This question will allow you to determine students' misconceptions and confusion of the two.)
- How do scientists explain how evolution occurs?
(This question should help students in distinguishing the theory of natural selection from the observed fact of evolution.)
- Do you think that the way people have explained evolution has changed over time? Why or why not?
- Who was Charles Darwin?
- How did Charles Darwin explain how evolution occurs?
- When did Charles Darwin propose his theory about evolution?
- Did evolutionary theory exist before Darwin?
- How do you think Darwin developed his theory?
- Do you know of any other individuals who proposed theories on evolution?
Tell students that they will examine writings from three influential scientists who proposed explanations for biological evolution—Jean Lamarck, Alfred Russel Wallace, and Charles Darwin.
Assign the Lamarck reading, Zoological Philosophy, and have students answer the questions posed by the History of Evolutionary Theory student sheet. Students can also use their esheet to access the reading. In class the next day, discuss the Lamarck reading. Before asking questions, allow students the opportunity to ask their own questions about the vocabulary or reading that they may have found confusing. Encourage other students to answer these questions. Once students have cleared up any misunderstandings or confusion, move on to a discussion of the assigned questions.
The exact mechanism proposed by Lamarck should be clear from the reading. Lamarck believed that individuals change over time due to environmental influences and these "acquired" characteristics are then passed on to the offspring. Over time, all the individual organisms that have been subjected to that particular environment will have changed. Implicit in this assertion is that species change as the result of the "needs" of individuals. Although it is not mentioned in the reading, the data that provided the foundation for some of Larmarck's inferences came from the fossil record. Specifically, he argued that the fossil organisms that we no longer see on earth have not become extinct, but rather have changed to such an extent that we no longer recognize them as being the same. The gradual accumulation of these changes over time accounts for the changes that are evident in the fossil record.
Discuss with students the example of the giraffe described by Lamarck as evidence for his theory. According to his theory, a giraffe's long neck developed as a result of the animal's need for leaves on the tops of trees. Over time, the giraffe's organs were strengthened to support long necks, and hence its offspring were also endowed with long necks. Ask students:
- Why has this example been criticized by other scientists?
(Individual giraffes cannot change the length of their neck because of a “need” to reach leaves high on a tree. Moreover, individuals can only pass on hereditary material, not a trait acquired due to environmental influences.)
- If we now know that Lamarck's theory was incomplete, why do we still study it today?
(First, Lamarck's theory of evolution attracted so much heat from religious conservatives that it depleted their reserves and their will to resist. Second, Lamarck had cleared the way towards developing a complete theory of explaining evolution and the diversity of life. Both Charles Darwin and Alfred Russel Wallace built upon the foundations of evolutionary thought laid down by Lamarck. Armed with additional ecological knowledge and worldly experience, they independently developed a durable theory of evolution by natural selection.)
Next, assign the Wallace reading, On the Tendency of Varieties to Depart Indefinitely from the Original Type, and have students answer the questions posed on the History of Evolutionary Theory student sheet. Students can also use the esheet to access the reading. Tell students that Alfred Russel Wallace was a friend of Darwin's, working as a naturalist in Malaysia. He sent Darwin his short paper entitled, "On the Tendency of Variations to Depart Indefinitely from the Original Type." In class the next day, discuss the Wallace reading. As before, first allow students the opportunity to ask their own questions about the vocabulary or reading that they may have found confusing. Encourage other students to answer these questions. Once students have cleared up any misunderstandings or confusion, move on to a discussion of the assigned questions.
Finally, assign students the Darwin reading, On the Origin of Species, and have students answer the questions posed in the student sheet. Tell students that they will read an excerpt from his book, On the Origin of Species published on November 24, 1859, 23 years after the conclusion of his voyage on the H.M.S. Beagle. As a side note, students may be interested to know that by the end of the day, the entire first edition (1250 copies) was sold out.
After discussing general questions and the reading questions, ask students:
- Do you think Darwin's argument was scientific? Why or why not?
(Darwin's argument was a scientific one; he used his observations and knowledge available at the time to develop a sound theory that would explain biological evolution.)
- Do you think Darwin's argument was more or less scientific than Lamarck's? Explain.
(Both Darwin's and Lamarck's theories were scientific in that they were reasonable, used observations as data, and relied on the knowledge available at the time. However, we know from our knowledge of genetics and heredity that Lamarck's theory was incomplete. Darwin's theory, however, is consistent with genetics although he had no knowledge of the principles of heredity in his lifetime.)
- Compare Darwin's theory to that of Wallace's. How were they the same or different?
(Both had the same theory. Darwin even credits Wallace for sending him his paper and the two presented their ideas together.)
- Why do you think Darwin is more famous than Wallace, even though we know that they both had the same theory and both presented their findings together?
(The last published work of Darwin was On the Origin of Species, published 1859; hence, most of the credit of evolutionary thought has been given to Darwin. However, Darwin and Wallace were good friends and colleagues and Darwin mentions Wallace numerous times in his book, particularly in his introduction.)
Answers to the questions posed on the student sheet can be found in the History of Evolutionary Theory teacher sheet.
Tell students that their assessment assignment is to describe the history of evolutionary theory. Students can choose to demonstrate their understanding and knowledge in any appropriate format, such as video, illustrations, poster, essay, or diorama. Specifically, students should discuss/describe the events and people, besides Lamarck and Wallace, which influenced the development of Darwin's theory.
Refer students to the "Understanding What You Learned" section of the History of Evolutionary Theory student esheet. Go over the assignment with students and assign a due date.
Follow this lesson with the Science NetLinks lesson: Comparing Theories: Lamarck and Darwin.
Before beginning a unit on evolution, administer a survey to elicit students' misconceptions about this topic. Rather than grading these surveys and telling students which of these answers are "right" or "wrong," have students keep their surveys and repeat them at the conclusion of the unit. Then, ask students to compare their responses before and after the unit. At this point, also discuss each statement and explain why certain points are true or false in accordance with scientific understanding of biological evolution. This Evolution Survey from the University of Indiana is a good example.
To connect this lesson with social studies and world history, have students draw the history of evolution timeline as shown on the PBS Evolution website on a smaller scale (3-4 sheets of paper). On the bottom half of the timeline, have students label the 31 events from the "Rise of Evolution" segment. On the top half, have students add events from world history that coincide with the changes in evolutionary thought. Students can research world history events from the Hyper History website. This will give students a better understanding of when the changes in evolutionary thought took place. It will also encourage students to consider how world events may have affected the development of evolutionary thought and vice versa.
Evolution Library contains annotated links to a wide variety of useful articles, videos, Web resources, and other tools that can be used to supplement the teaching of evolution.