To explore the factors that control variation in human skin color and the implications of this information for human society.
This lesson is part of the Skin Deep Project, which examines the science behind skin. Skin Deep is developed by AAAS and funded by Neutrogena. For more lessons, activities, and interactives that take a closer look at the science behind skin, be sure to check out the Skin Deep Project page.
In this lesson, students will learn about the factors that determine skin color and how adaptation and natural selection contribute to its variation. They will come to understand that skin color is no longer considered a credible scientific standard by which to classify people into different races
Diversity of human appearance and form has intrigued biologists for centuries, but nearly 100 years after the term “genetics” was coined by William Bateson in 1906, the genes that underlie this diversity are an unsolved mystery. There is a tremendous range of human skin color in which variation can be correlated with climates, continents, and/or cultures, yet we know very little about the underlying genetic architecture.
This lesson seeks to continue to impress upon students at this level that while people vary in size, shape, skin color, body proportions, body hair, facial features, muscle strength, and so on, human beings are all one species. Compared to the internal similarity of all humans, these differences are minor, as demonstrated by the fact that people from anywhere in the world can physically mix on the basis of reproduction, blood transfusions, and organ transplants. Furthermore, as great as cultural differences between groups of people seem to be, their complex languages, technologies, and arts distinguish them from any other species. (Science for All Americans, p. 72.)
It is recommended that teachers at this level move students toward a more sophisticated understanding of the features of organisms—in this case people—that connect or differentiate them: from external features and behavior patterns, to internal structures and processes, to cellular activity, to molecular structure. This lesson helps to fulfill the two aims that dominate at this grade level. One is to advance student understanding of why diversity within and among species is important. The other is to take the study of diversity and similarity to the molecular level. (Benchmarks for Science Literacy, pp. 101, 105.)
In their ongoing study of evolution and natural selection, students will benefit from recognizing that, by its very nature, natural selection is likely to lead to organisms with characteristics that are well adapted to survival in particular environments. (Science for All Americans, pp. 68-69)
In terms of reacting to and integrating the social implications of there only being one race of human beings, this lesson seeks to help students understand more deeply that one can be proud of one's own cultural origins without having to denigrate other cultures. Religious, racial, language, and national prejudices are deep, generational, and not easily eliminated, but at least students can realize that those attitudes are part of everyone's cultural inheritance. They can become familiar with the effects such attitudes can have on human behavior. Even further, the ultimate challenge is to help students make sense of behavior patterns that may seem puzzling out of the context of cultural diversity. Although students might be able to describe cultural influences on other people's thinking, the tougher goal is for them to see what influences have an effect on their own ideas and behavior. (Benchmarks for Science Literacy, pp. 151-56.)
Students at this grade level hold a number of misconceptions about topics related to skin color variation. For example, high-school students have difficulties understanding the notion of natural selection. A major hindrance to understanding natural selection appears to be students' inability to integrate two distinct processes in evolution, the occurrence of new traits in a population and their effect on long-term survival. It also has been found that high-school students may have difficulties with the various uses of the word "adaptation." In everyday usage, individuals adapt deliberately. But in the theory of natural selection, populations change or "adapt" over generations, inadvertently. In addition, students of all ages often believe that adaptations result from some overall purpose or design, or they describe adaptation as a conscious process to fulfill some need or want. (Benchmarks for Science Literacy, pp. 343-344.)
Teachers might want to keep in mind that before students can reason about different world views, they often have to abandon the belief that some human cultures are biologically subordinate. An obvious complication here is that students tend to impose contemporary values and ideas from their own culture upon other cultures. (Benchmarks for Science Literacy, p. 346.)
Ideas in this lesson are also related to concepts found in these health education standards:
- Health Education Standard 2:
Students will analyze the influence of family, peers, culture, media, technology, and other factors on health behaviors.
2. analyze how culture supports and challenges health beliefs, practices, and behaviors.
Before the lesson, for the activity in the Motivation section, you will need to write the simple descriptions for the six different skin types found at Fitzpatrick Skin Type on large pieces of paper and tape them up in six different parts of the room.
Using the Fitzpatrick Skin Type resource, copy and post descriptions of the six skin types around the room. Ask students to walk around the room, find the description that they think best matches their skin type, and stand near the description. Then have students in each group take seats together and discuss questions like these:
- How would you describe your skin type?
- What do you do to protect your skin? Why is that important?
- What other characteristics do members of your group have in common?
- What factors influence skin color?
- How does your skin compare with that of other family members?
- What geographical regions are your ancestors from?
Ask a member of each group to present a short summary of their discussion to the class. When all group reports have been presented, lead the entire class in comparing and contrasting the skin types and drawing generalizations.
Questions for them to consider may include:
- How do the skin types differ?
- What similarities do they have?
- What can you deduce about these skin-type groups?
- Are there any social implications for membership in each group?
(Accept all reasonable answers. Encourage students to elaborate on their responses.)
After this consideration of their skin type and its social implications, students will be prepared to examine the factors that influence variation in skin color in greater depth.
Divide the class into three groups. Assign to each group one of the skin-variation resources below to read and report on to the rest of the class. Students should use their Variation in Human Skin Color student esheet to go to their assigned resource. Have each group answer the corresponding questions on their Resource Questionnaire handouts. Explain that it will be their job to teach the class what they have learned about skin variation from their assigned resource, using their answers to the questions as a framework. They also will be expected to listen and take notes on what they learn from the other groups’ presentations.
Resource presentations should be done in chronological order.
- Resource #1: Modern Human Variation: Overview
- Resource #2: Skin Color Adaptation
- Resource #3: A New Light on Skin Color
When the groups have finished their presentations, the class as a whole should review and discuss what they have learned. Students need to recognize that skin color is an alterable characteristic that results from adaptation in a specific environment that has survival value for the organism and may then be perpetuated by the process of natural selection.
Focusing on the biological similarity that underlies skin-color variations should equip students to critically evaluate the improper use of differences in skin color to divide humans into distinct races. To help students integrate what they have learned and recognize the social implications of skin color, have them answer this question in a journal entry:
- How does what you have learned about variations in skin color affect your view of other people and the world?
Divide the class into pairs. Have each pair discuss their journal entries and create a poster informing the public about what determines skin color and how we should treat other people individually and as a society based on this knowledge. Have the pairs explain their posters to the class and display them on the bulletin board.
Students may appreciate reading an article in Science magazine, Zebrafish Researchers Hook Gene to Human Skin Color, about how an international team of researchers were able to identify a zebrafish pigmentation gene and its human counterpart, which is thought to account for a significant part of the difference between African and European skin color.
To further their learning on the topics of this lesson, encourage students to visit Syracuse University’s resource All of Us Are Related, Each of Us Is Unique, an exhibition designed to contribute to contemporary discourse on human diversity. It is a graphic presentation of biological findings rooted in genetics research that includes striking displays of phenotypic variations and evidence on human migrations and adaptations, while showing how erroneous conventional wisdom has been with respect to the deeply ingrained concept of discrete "races."
Students can learn more about the science, social, and historical aspects of race and how people are classified by visiting the online companion to the popular PBS documentary series, Race: The Power of an Illusion.
Students may enjoy learning about human evolution by visiting the Becoming Human website. The site content includes a broadband documentary (organized by evidence, anatomy, lineages, and culture), related educational interactivities, lesson plans, resources, and current news and features.