To compare Lamarck's mechanism for evolution with Darwin’s theory of natural selection.
This lesson provides an opportunity for students to compare the theories of two historically important evolutionary scientists: Jean Baptiste Lamarck and Charles Darwin. In this lesson, students explore the basic principles behind Darwin's mechanism of natural selection. They then extend their understanding of Lamarck's and Darwin's models by using them to explain phenomena and by comparing them to one another. Furthermore, this lesson presents a helpful way of concluding an examination of Lamarck's ideas and preparing for a more in-depth study of Darwin's model of natural selection.
In previous lessons, students should have examined Lamarck's hypothesis. In this activity, students are introduced to the principles of natural selection using an online animated movie. Students then present their own ideas about evolution by proposing explanations of observed characteristics of animals, such as the speed of cheetahs or the behavior of naked mole rats. They are then asked to distinguish between a Lamarkian explanation and a Darwinian explanation for the development of long legs in wading bird species such as herons and egrets. Finally, students work in pairs to develop their own scenarios using Lamarck's and Darwin's models to explain the origin of island bird species. The goal of these exercises is for students to critically examine two models that explain the observed biological evolution and diversity of life on earth. Through repeated encounters with Lamarkian and Darwinian explanations, students will have the opportunity to determine why the Darwinian model is more plausible and therefore accepted by the scientific community today.
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). The apparent confusion may be reflected in statements such as "leopards evolved their spots in order to survive better in their environment," or "elephants evolved their large ears so that they could disperse their body heat better." 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. In this lesson, students are asked to explain phenomena using both Lamarckian and Darwinian theories. In doing so, students will come to see that the Lamarkian explanation is unsatisfactory while the Darwinian mechanism of natural selection is plausible and consistent with our current knowledge of genetics.
Tell students that they will look at Darwin's model of natural selection a little more closely and then compare his model to that of Lamarck's.
Ask students these questions. As students discuss and answer these questions, note student responses on chart paper or the board and save. These questions are designed to pre-assess student understanding and misconceptions about the theory of natural selection. After students have completed the motivation assignment, review the questions again and note student responses next to their original statements. This will allow students an opportunity to reflect on their own ideas and learning.
- What is natural selection?
- Is it a fact or a theory?
- What is the difference between natural selection and evolution?
- The main problem faced by evolutionary biologists was the issue of the origin of species. How did Lamarck explain how new species emerge?
- How did Darwin explain how new species emerge?
- Do you think there was any similarity in the models proposed by the two scientists? Explain.
- What are the main differences between the two models?
Refer students to the Comparing Theories student E-Sheet. Review the directions and technical issues with the class. If students are unfamiliar with the BrainPOP movies and viewing controls, pull up a different movie from the science index on a class computer connected to a classroom monitor. Show students how to use the four viewing control buttons to skip back a section or to pause, rewind, and fast-forward the film. Assign the activity for homework.
In class, after students have completed their assignment, discuss the questions. Re-ask the pre-assessment questions and note student responses next to their original statements. Have students reflect on the responses that changed due to a better understanding of Darwin's theory of natural selection.
Divide students into small groups of four. Assign each group a question from the Evolution Problem Solving Questions found on the Comparing Theories: Lamarck and Darwin teacher sheet packet. Tell students that they have 10-15 minutes to answer the question with their group. Remind students to think of both Lamarck's and Darwin's theories as they come up with their response. Pass out a copy of Lamarck and Darwin: Summary of Theories student sheet for each group. At the end of the allotted group work time, have one student from each group present the question and proposed answer to the rest of the class. If there are more than three groups in your class, have the two groups with the same question present one after the other. This will allow other students to compare responses. As students present, encourage students to ask questions.
More than likely, many of the groups will present Lamarckian ideas. When students represent Lamarckian theory, they refer to individual organisms acquiring new characteristics because they "need to" or "want to." They also believe that organisms can pass these acquired traits onto their offspring. When students represent Darwinian theory, they describe that a population changes because certain heritable traits, already present in the population, help organisms to survive and reproduce better. Students using Darwinian theory will use words like "on average," "population," and "over many generations."
The important points that need to be illustrated and discussed by you, especially if they do not arise from student discussion, are:
- Evolution proceeds by the process of variation, a genetically random process, and selection, an environmentally driven non-random process.
- Organisms do not get what they "need" through "inner wants" or through "use and disuse.” Individual intentions do not play a role.
- Acquired characteristics are not passed on to offspring.
- Mutations are not directed for the benefit of the individual.
- Evolution is neither random nor goal-directed. It is, in fact, driven by the non-random and non-directed process of natural selection.
Provide each student with the Comparing Mechanisms of Evolution: A Sample Study student sheet. Have students work in pairs to answer the five discussion questions based on the reading. Discuss the questions in class.
After students have discussed the questions, go over the "Developing Scenarios" section of the student E-Sheet. If possible, go to the PBS Evolution presentation of An Origin of Species with your class. Read the introduction with the class and describe how the pollenpeepers are modeled after the numerous species of honeycreeper birds on the Hawaiian Islands. Show students how to navigate through the map, timeline, and text boxes in order to determine the environmental pressures and history of bird evolution. Remind students that the question faced by both Lamarck and Darwin was how to explain this observed diversity of life. Their assignment is to work with their partner and develop plausible explanations that would be proposed by both evolutionary scientists.
Refer students to the "Understanding What You Learned" section of the student E-sheet. Read the problem aloud and go over any confusing vocabulary or terms.
Many insular species of both plants and animals have lost defense mechanisms that are frequently found on their continental relatives. Several species of birds and insects have become flightless and many plant species have lost defense mechanisms such as thorns or toxic chemicals. How would an evolutionary biologist explain how these losses came about?
Tell students that their assignment is to answer this question in essay format using their knowledge of evolutionary theory. Alternatively, present this question in class as a journaling activity.
Access Excellence provides a fun lesson on Darwin and Lamarck's dueling theories in the form of a court case. This activity allows students to role-play while learning theories of evolution. Examples of roles played by students include court reporters, a bailiff, witnesses, as well as Darwin's and Lamarck's attorneys. The goal of the prosecution is to prove Lamarck's theory of Use and Disuse and Transmission of Acquired Characteristics to be correct. The defense attempts to prove Darwin's theory of Variation and Natural Selection to be correct. Students conduct research, interview witnesses, ask investigative questions, and examine evidence from each side to determine which model best explains biological evolution.
Have students present the "Evolution Problem Solving Questions" to members of their community, including other teachers, parents, and students. Students should record the responses in written (e.g., survey or written responses) or audio-visual format (e.g., tape recorder or camcorder) and determine if most people are using Lamarkian or Darwinian explanations. Students can then work on a large poster presentation comparing Lamarck's hypothesis to Darwin’' hypothesis and display the information outside of the classroom to educate their teachers and fellow students.
Modeling for Understanding in Science Education provides a unit on Natural Selection for use in middle- and high-school classrooms. One of its lessons, Comparison of the Models, has students compare the theories of Lamarck, Darwin, and William Paley, a nineteenth century theologian who invoked the supernatural to explain adaptation. This activity allows students to also examine the theory of intelligent design in explaining the observed diversity of life.