The Biology of Skin Color

Contributor
HHMI - Biointeractive
Type Category
Instructional Materials
Types
Lesson/Lesson Plan , Activity , Data
Note
This resource, vetted by NSTA curators, is provided to teachers along with suggested modifications to make it more in line with the vision of the NGSS. While not considered to be “fully aligned,” the resources and expert recommendations provide teachers with concrete examples and expert guidance using the EQuIP rubric to adapted existing resources. Read more here.

Reviews

Description

 

This lesson is designed to accompany a short film by HHMI BioInteractive. In the film, Penn State University anthropologist Dr. Nina Jablonski discusses the evidence for the natural selection of human skin color. She describes how the phenomenon of skin color variation is related to both global distribution of UV intensity and the need for the skin to absorb some UV to produce vitamin D. The video briefly covers related topics in physiology, UV light absorption, genetics, and gene regulation. A student worksheet is designed to accompany the video, but partitions the information into shorter sections with additional data. Students use this data to make predictions about how skin color has evolved over time to include the variety of pigments we see around the world today. Besides the video and student worksheet, this resource includes educator materials, a film guide, and a video about additional educator tips. A Spanish version of all materials is also available.

Intended Audience

Educator and learner
Educational Level
  • High School
Language
English
Access Restrictions

Free access - The right to view and/or download material without financial, registration, or excessive advertising barriers.

Performance Expectations

HS-LS4-4 Construct an explanation based on evidence for how natural selection leads to adaptation of populations.

Clarification Statement: Emphasis is on using data to provide evidence for how specific biotic and abiotic differences in ecosystems (such as ranges of seasonal temperature, long-term climate change, acidity, light, geographic barriers, or evolution of other organisms) contribute to a change in gene frequency over time, leading to adaptation of populations.

Assessment Boundary: none

This resource is explicitly designed to build towards this performance expectation.

Comments about Including the Performance Expectation
The activity guides students through a series of questions that helps them figure out several concepts about skin color and how it has evolved over time. The performance expectation explicitly calls out how natural selection leads to evolution and evidence of this can be found in part 1 question 10 of the activity guide, “Based on what you know about skin pigmentation so far, suggest a mechanism by which UV intensity could provide a selective pressure on the evolution of human skin color. In other words propose a hypothesis that links skin color to evolutionary fitness.” Making a claim is the first step in creating an explanation. As students progress through the lesson, they will continue to gather evidence in order to support their claim or disprove it.

HS-LS4-2 Construct an explanation based on evidence that the process of evolution primarily results from four factors: (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment.

Clarification Statement: Emphasis is on using evidence to explain the influence each of the four factors has on number of organisms, behaviors, morphology, or physiology in terms of ability to compete for limited resources and subsequent survival of individuals and adaptation of species. Examples of evidence could include mathematical models such as simple distribution graphs and proportional reasoning.

Assessment Boundary: Assessment does not include other mechanisms of evolution, such as genetic drift, gene flow through migration, and co-evolution.

This resource is explicitly designed to build towards this performance expectation.

Comments about Including the Performance Expectation
The student activity addresses three of the four identified pieces within the performance expectation. In order to address the remaining piece, “competition for limited resources,” a class discussion around this topic could be included. Students could be prompted with questions about why they think people started to move from where they lived in the first place. An example question could include, “Thinking about how ancient populations lived, what might be one reason these people would decide to move away from the their native equatorial homes?” following with “How did this migration cause skin color to change?”

Science and Engineering Practices

This resource is explicitly designed to build towards this science and engineering practice.

Comments about Including the Science and Engineering Practice
The activity does address the full element of the practice in certain questions (13, 17 and 20), however a teacher could increase three-dimensionality by rewording some additional questions. For example, in part three of the activity question 18 reads ‘Based on these data, describe the populations least likely to synthesize sufficient levels of vitamin D. Explain your answer with data from the table.’ To make the question three dimensional the teacher could change the wording to: Citing specific evidence from the data, explain which population would be least likely to synthesize sufficient levels of vitamin D and explain your reasoning.

This resource is explicitly designed to build towards this science and engineering practice.

Comments about Including the Science and Engineering Practice
During the lesson students are asked to analyze data given in graphs;however they are not engaged in the collection of data, or the use of any tools or technology. In order to address this full element the teacher could incorporate an investigation using UV beads in order for the students to collect first hand data. Students could test different sunscreens or sunglasses using UV beads and compare their results. Using these tools and technologies will better address the element of the practice and give students an additional piece of data to use in their analysis.

Disciplinary Core Ideas

This resource is explicitly designed to build towards this disciplinary core idea.

Comments about Including the Disciplinary Core Idea
There is explicit evidence that this lesson addresses parts 1 and 4 of the performance expectation as written. In order to address the entire PE a teacher could: add a section to address part (2) the genetic variation of individuals in a species due to mutation and sexual reproduction. How does sexual reproduction affect melanin when parents are not of the same skin color or when offspring are born with a melanin mutation (albino)? Teachers could develop a class discussion piece around part (3) of PE competition for limited resources - these could include ideas of why people started to move to new geographical locations. How might competition for resources influence the global distribution of skin color?

This resource is explicitly designed to build towards this disciplinary core idea.

Comments about Including the Disciplinary Core Idea
There is explicit evidence demonstrated in part 1 question 11 to show that this DCI is addressed. The question, “What does it mean for a trait, such as light skin coloration, to be under negative selection in equatorial Africa?” and having students relate negative selective pressure to what we know about MC1R allele diversity among African populations is an example of this. This question addresses both parts of the DCI - variation in the genetic information among organisms in a population (different populations have different kinds of melanin) and variation in the expression of that genetic information (different skin colors within populations). Asking a corresponding question here would give the teacher a way to formatively assess students’ understanding. An example question could be: “As populations move away from the equator would light skin color still be considered a negative selection pressure? Using what you know about skin coloration, explain your answer.”

Crosscutting Concepts

This resource is explicitly designed to build towards this crosscutting concept.

Comments about Including the Crosscutting Concept
Evidence - Part 2 Question 12 of the activity reads (correlation): Why does Dr. Jablonski dismiss the hypothesis that protection from skin cancer provided selection for the evolution of darker skin in our human ancestors? Evidence (cause) - Describe the relationship between folate and UV exposure. Use specific data from the graph to support your answer. Teachers may want to have a discussion that addresses the idea of correlation as this can sometimes be a difficult concept for students. This first question demonstrates a correlation between increased melanin and skin cancer and not a cause/effect relationship. Although darker skin helps protect individuals from skin cancer, skin cancer was not the selective pressure that caused skin color to evolve. However, in Question 2 students use the evidence presented in the video related to the production of folic acid and its importance in reproduction to UV exposure in order to show a cause/effect relationship. Later, students are asked to explain how this cause/effect relationship between between UV and folic acid production perpetuated the variety of skin color we see today. Teachers may have students explain why the first question is a correlation and the other is causation in order to make sure they understand the difference.

This resource is explicitly designed to build towards this crosscutting concept.

Comments about Including the Crosscutting Concept
Teachers could refer to skin color as the phenomena in order to address the whole element as identifying the phenomena is part of the cross-cutting concept. The cross-cutting concept of patterns is addressed throughout the activity since in part one students are looking at skin color in relation to the equator. Later they look at the patterns of melanin production in relationship to folic acid. To emphasize this CCC, teachers may want to ask students where they used patterns to analyze data or how data patterns help them figure out the phenomena.

Resource Quality

  • Alignment to the Dimensions of the NGSS: No explicit phenomena is given - skin color is the implied phenomena. In order to improve this resource a teacher would need to explicitly call out skin color as the anchoring phenomena within this activity. Engagement with all three dimensions in order to explain a phenomena is implied throughout the lesson. Specific pieces of all three dimensions are called out specifically but using them together is implied. Students engage in three-dimensional learning by analyzing multiple pieces of data, watching a short film, and participating in a written activity in order to make sense of the phenomenon of skin color variation and how it has evolved. Examples given with the lesson include: *describe the relationships between the UV index and latitude *write a hypothesis for where in the world you would expect to find human populations with darker or lighter skin pigment *propose a hypothesis that links skin color to evolutionary fitness *Describe predicted effects of using a tanning booth Tips: *When starting the lesson it is suggested that a teacher make the phenomenon of skin color explicit. This could be a picture of people all with different skin colors and include a driving question such as: Why doesn’t everyone have the same color of skin? *Reword questions in order to make the dimensions explicit, for example: *Analyze the graph in order to explain the patterns between the UV index and latitude *Use your data to make a claim for where in the world you would expect to find….cite specific evidence and explain your reasoning. *Explain the cause/effect relationship between… This lesson could also be expanded in order to cover the entire DCI.

  • Instructional Supports: The lesson includes two teaching tips that state: students can work independently or in small groups and the teacher may want to project the figures and examine them together as a class and then let students answer questions individually. This lesson also includes a video about one teacher’s suggested use of the video in class and others written suggestions. These can be found on the same page as the video, however neither are written into the lesson as supports. There is a Spanish version of the materials and a video option with subtitles, however no specific instructional supports are given for English Language Learners, students with special needs, or advanced learners. Suggestions: *Provide a transcript of the video as reference so students that may struggle with listening skills may refer back. *Teacher could also allow students who may need extra time to watch the video independently. *Provide writing guides or graphic organizers for extended response questions.

  • Monitoring Student Progress: The student worksheet breaks up the video into four parts and the educator materials contain an answer key. However, here is no explicit guidance on how to monitor student progress. To more effectively monitor student progress, teachers may want to *use a teacher check list of ‘look fors’ and have a whole group discussion after each section to identify student understanding and misconceptions. *check student questions after each sections before letting them move on to the next part. *check student understanding with a quick quiz or exit ticket at the end of a section and provide feedback

  • Quality of Technological Interactivity: