Do you see what I see? Light, sight, and natural selection
Students are engaged throughout this unit with various activities that explore optical illusions, color perception, color-blindness, and diversity of vision across species. After examining the physical properties of light and the structure and function of the mammalian eye, students apply their knowledge in designing an experiment to test color preference in guppies. These experimental results are tied into our very popular Guppy Game (featured in NSTA’s The Science Teacher) in which students role-play guppies to experience how color and habitat affect survival and reproduction as a part of natural and sexual selection.
This unit connects to research led by Dr. Becky Fuller at the University of Illinois.
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This introductory lesson serves to motivate the unit “Do you see what I see?” by targeting individual differences in visual perception. Here, the unit’s driving question is introduced and students begin to examine the driving question by probing the basics of visual perception. Focus is directed at how and why people sort colors in different ways and how they perceive colors. Activities include a paint chip sorting activity, optical illusions, eye dissections, and a traditional colorblind test. The lesson activities are used to motivate students’ interests in learning more about what and why they see what they do, introduce information about how humans perceive contrast and color, and the anatomy of the visual system including the eye. Students return to these ideas throughout the unit as they develop a response to the driving question.
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In Lesson 2, students test how their own perceptions are affected by environmental conditions through sorting candies. During this activity, students attempt to remove all the candy-coated chocolates of a certain color and then test how different environmental conditions (e.g. light color and background color) may affect their speed and accuracy. This activity is a good opportunity for teachers to address key concepts of how the eye works and how we perceive color. This lesson builds on ideas introduced in the previous lesson. -
Students continue to learn about the physiological basis of vision introduced in Lesson 1, while extending their understanding to the basic optical principles that underlie vision. By using spectrophotometers and prisms to investigate the absorption, transmission, emission and reflection of light, students explore the differences between their visual perceptions and the physical properties that contribute to them.
View Curriculum Materials for Lesson 3: Is seeing believing?
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This lesson provides an engaging central activity that will be complemented by discussions and activities about the use of guppies as a model for color preference, creation and interpretation of graphs to represent data, and continued discussion about human color perception.
Using a penny-pecking experiment, students increase their understanding of fish color preference and of data collection, analysis, and presentation. Discussions of data collection and interpretation are fundamental to this lesson. Students come to a consensus about the experimental design before working in groups to run the experiment. Students decide how to interpret compiled class data during a whole-class discussion focused on making meaning from all of the experiments.
The experiment and discussions about the data builds on the color-sorting task in Lesson 1 and prepares students for discussions about the interactions between color and the environment in Lesson 5. Students have begun to think about color perception as a complicated neurological process. They have learned that their own experiences (Lesson 1) and environment (Lesson 3) influence the perception of color. In this lesson, students examine whether the same principles apply to fish color preference.
View Curriculum Materials for Lesson 4: Do fish have a favorite color?
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Using the penny-pecking protocols established in Lesson 4, students examine how the environment impacts what color fish prefer to peck in Lesson 5. The activity in this lesson develops connections between the human example in Lesson 3 and other organisms by having students develop an investigation using guppies and their findings from Lesson 4. By drawing on what they learned about optics and sensory physiology in Lesson 2, students investigate how variations in optical properties of the external environment can lead to variations in an animal’s visual perceptions and, consequently, its mating and food preferences. In addition, the concept of variability within biological populations is addressed. This lesson also emphasizes the development, testing, evaluation, and revision of a hypothesis based on prior knowledge and intuition developed from related experiments.
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In this lesson, students will examine how natural and sexual selection can help to explain why guppies are attracted to different colors. Students will analyze different sensory biases that help a fish survive (such as being able to find different colors of food, or being camouflaged to avoid lurking predators), and how these biases can also affect sexual competition (fish who are brightly colored or have body coloration similar to preferred foods might be more attractive to mates). By playing The Guppy Game students will observe how different varieties of fish are adapted to different environments. They can observe male-female differences and make hypotheses about which habitats will favor which traits. By simulating different populations of guppies under different circumstances students can observe genetic drift in populations over time.
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In this culminating lesson, students use the knowledge they learned in the previous lessons to make inferences about the significance of color perception and connections to other organisms. Students discuss the biological advantage of color vision for humans during the synthesizing Advantage of Color Vision activity and make connections to other organisms and different visual systems in the Vision Adaptation activity. Students learn about the evolution of color vision, how “evolution is devolution,” and how animals evolved to have the most efficient visual system for their needs, and not necessarily the most complex visual system.
