The Empirical Challenges of Racial Classification
Developed by Scott Bronson

Grade Levels: 9-14
Subject Matter: Biology, Anthropology, Genetics, Geography
Time Allotment: 2-3 class sessions
Description: This lesson will help students examine their preconceptions and assumptions about racial categories and understand the impossibility of constructing a consistent system of human racial classification.

Scott Bronson is Education Manager at the Dolan DNA Learning Center of Cold Spring Harbor Laboratory in New York. He is featured in Episode 1 of the series.


Most people still believe that the world's people come divided into separate, biologically distinct groups called "races," distinguished by physical characteristics such as skin color, eye shape, and hair texture. The idea of race assumes that variation in these superficial traits correlates with other innate differences, including intelligence and aptitude - in other words, that members of one race are fundamentally more similar to each other than to members of another race.

Human beings across the world do in fact vary in their physical appearance and genetic composition. And traits like skin color, eye shape and hair texture are influenced by genes we inherit from our parents. But do patterns of human variation map onto "races"? Why do we classify the way we do, using some traits while ignoring others? Is there a logically consistent way of assigning individuals to a biological "race"?

This lesson will help students discover the fuzzy, inconsistent nature of racial classification - including how and why patterns of human variation defy racial categorization - and learn about some of the hidden values and assumptions that underlie the reasons we classify the way we do.

Students will first explore their own preconceptions about race by sorting themselves according to which race they think they belong to and listing the criteria they used. Students will then be asked to re-sort themselves according to several of their own observed genetic traits. These results will be compared within and between "races" to explore the impossibility of consistent human racial classification.


gradual variation
within-group vs. between group variation
natural selection
sexual selection
gene flow


  1. Confront the inconsistencies inherent in any attempt to classify humans according to innate racial categories.
  2. Better understand patterns of human variation, including how the geographic distribution of physical traits does not follow racial lines but rather cuts across them.
  3. Introduce three basic concepts of human biodiversity: gradual variation, non-concordance and within-group vs. between-group variation.
  4. Understand the importance of logical consistency in scientific reasoning and experiments.
  5. Contribute information to a group project.



ACTIVITY #1 - Articulating Preconceptions: What Do Students Believe?

Brainstorm the different races of the world and list all the "races" across the top of the blackboard. Students might use different and inconsistent kinds of labels for their races (see below). This should not be discouraged.

Have students physically group themselves in the classroom according to the race they think they belong to. When everyone has joined a group, ask each group to generate a list of the criteria for membership in their "race" (e.g., skin color), and post the list on the blackboard under their respective racial label. NOTE: Some students may resist joining any of the designated racial groups. That's okay, but they must then add whatever label each would apply to him or herself to the list of racial labels, even "human being."

As a class, briefly note and discuss any inconsistencies across racial labels - for example, categories based on anthropology (Mongoloid, Caucasian, Negroid) vs. color (Yellow, White, Brown, Black) vs. geography (Asian, European, African) vs. ethnicity (Arab, Jew, Kurd, Hmong) vs. nationality (Mexican, Puerto Rican) vs. language (Hispanic), etc. - and similarly discuss the membership criteria listed on the board. Are they all comparable?

ALTERNATE ACTIVITY #1 - For racially homogenous classes

Ask your students to do the "Sorting People" activity on the companion Web site.

This interactivity challenges users to "sort" 20 people (images provided) into five federally recognized categories. Once they finish sorting, students learn (a) how the U.S. government would classify these people; (b) how each person self-identifies; and (c) each person's ancestry. Students can then move on to the "Explore Traits" activity where the same 20 people are re-sorted according to skin color, blood type and fingerprint type.

ACTIVITY #2: Problematizing Student Assumptions: Creating an Inventory of Traits

Screen the first five minutes of Episode 1 - The Difference Between Us, beginning with the opening titles (00:45 - 05:23; DVD Scene #2) - this is Clip A. To view a complete transcript of the episode, click here.

Stop the video and ask your students if they too believe their closest genetic matches are with others in their own racial group. As a class activity, ask your students to brainstorm definitions of "race." List each definition on the board.

Pass out the Human Traits Inventory Worksheet (below), which lists several traits influenced by our genes. Have the students work in small groups to analyze their own physical traits and fill out the worksheet.

Inherited Trait
Hitchhiker's thumb (top joint can form almost 90-degree angle)    
Tongue curl    
Detached earlobe    
Skin color - Dark    
Skin color - Medium    
Skin color - Light    
Widows peak    
Hand clasp - Right thumb on top    
Hand clasp - Left thumb on top    
Fingerprint type (click here for examples) - Loop    
Fingerprint type - Whorl    
Fingerprint type - Arch    
Fingerprint type - Tented Arch    
Blood type A (ask parent, doctor, or clinic)    
Blood type B    
Blood type AB    
Blood type O    
Lactose intolerant    

Have your students re-form their original "racial" groups. Then, proceeding down the list of traits on the worksheet, ask the students to physically re-group themselves in the classroom by each successive trait (those with hitchhiker thumb on one side of the room, those without on the other side, etc.).

After going through the entire list, discuss the following: What do the students notice about the new groupings? Do any of them match up or co-vary with their original racial groupings? How would students divide themselves now on the basis of genetic similarity and difference, taking into account all of these traits? Would it be easier to categorize people according to race if we used more traits? Why or why not?

Now, have the class re-visit the original list of membership traits for each "racial" group generated earlier (these should already be listed on the blackboard). Discuss the following: Why did they choose some traits but ignore others when dividing into racial groups? Why do we assume that traits like skin color are more meaningful than whether or not your tongue curls or whether or not your earlobes are attached? What do students think of their earlier definitions of race?

NOTE: Many students may be troubled and confused as they begin to scrutinize the "commonsense" racial categories we have all taken for granted but never examined. This cognitive dissonance is to be expected. You might re-assure students that we're not claiming that race isn't "real" (see discussions of "social race" at the end of Episode 1 and the other two episodes), but that the biological criteria we use are fuzzy, inconsistent and don't correspond to real patterns of human variation.

At this point, if you have a diverse class, you might want to re-visit the common racial skin color labels (red, yellow, white, brown). Have the class divide into groups of eight or so, and have them compare their skin colors using the inside of their upper arms (as is done in the film). What do they find? Are all "Black" people really darker than all "white" people? What about individuals from East Asian, Latino and Native American backgrounds? South Asians? What color are they really? (This can be done even with a racially homogenous class, but is best paired with the "Explore Other Traits" activity in the Sorting People section of the Web site.)

ACTIVITY #3: Mapping Traits onto Racial Categories

Have students read Jared Diamond's "Race Without Color," from Discover Magazine (, which includes a discussion of how various inherited traits are distributed geographically.

Working in small groups, have students make a chart that groups populations into "races" for each of the following traits (NOTE: advanced classes may also want to research these traits in other populations for a more complete picture):

  • Dark skin/medium skin/light skin
  • Lactose tolerance/intolerance
  • Epicanthal eye-folds/no epicanthal eye-folds
  • Sickle-cell carriers/not sickle cell carriers
  • Shovel-shaped incisors/other incisors

Using different colored pins, have each group of students mark the geographical distribution of one of the traits on your classroom map. Alternatively, photocopy a world map and have each group mark the distribution of each of the traits on their map.

As a prelude to discussing the class's findings, ask your students to define "genotype" and "phenotype." Does phenotype always reflect genotype? What other factors might affect phenotype besides the genes? Note that with the exception of suntanning on skin color, the phenotypic traits above do closely reflect genotype. Emphasize that very few traits are influenced by only one gene. Most traits are influenced by many genes, interacting with each other and with the environment in a very complex dance that scientists have barely begun to understand.

Discuss the class's findings. What surprised students the most? Does the geographic distribution of these traits match up and co-vary with what we conventionally think of as races? Or do the traits cut across racial lines?

For further discussion, have students explore the Human Diversity section (select "Physical Appearance") of the RACE Web site to see how some of the traits we usually think of as racial are distributed geographically.

ACTIVITY #4: Why Racial Classification Doesn't Work - Understanding Gradual Variation, Non-Concordance and Within- vs. Between-Group Variation

We've now seen how difficult it is to find a consistent racial classification system that works for everyone. Show the following two video clips. As they watch, ask students to look for three underlying characteristics of human variation that explain why racial classification doesn't work.

CLIP B (5 minutes) - on skin color and gradual variation. Begins with Alan Goodman on the difficulty of measuring race, ends with Joseph Graves taking us on an imaginary walk from the tropics to the pole. (22:35-28:03; DVD Scene #8 [back up 20 seconds from the start of Scene #8 to include the statement by Alan Goodman about the difficulty of measuring race])

CLIP C (9 minutes) - on non-concordance and within-group vs. between-group variation. Begins with Alan Goodman talking about concordance, ends with the narrator explaining that sickle cell results from having ancestors who lived in malarial regions. (32:20 - 40:46; DVD Scenes #10, #11, #12)

To view a complete transcript of the episode, click here.

Before moving on to a discussion of why racial classification doesn't work, make certain your students understand sickle cell trait and the skin color stories told in the film. You can use the following handouts for this.

NOTE: For an excellent lab on how selective forces affect allele frequencies using the example of sickle cell, visit the Genetics Project Web site:

Sickle Cell Handout

Sickle cell anemia is a hereditary disease that arises from a single mutation (SNP or single nucleotide polymorphism) in one of the genes that code for the hemoglobin protein in our red blood cells. Hemoglobin carries oxygen through the bloodstream to the body.

People who inherit two copies of the mutated hemoglobin gene, one from each parent, get sickle cell anemia. Their red blood cells become sticky and stiff and sometimes become sickle shaped. These "sickled" cells tend to get stuck in the narrow blood vessels known as capillaries, blocking the flow of blood. Sickle cell anemia is a very painful disease and can be life threatening.

But the larger number of people who inherit just a single copy of the mutated gene are known as sickle-cell carriers. They usually don't become anemic and interestingly, sickle cell carriers tend to be resistant to malaria, a deadly disease.

Malaria is caused by a parasite carried by the Anopheles mosquito. After humans started practicing agriculture, the mosquito thrived in standing pools of water that appeared on the cleared land. Scientists believe that the sickle cell mutation arose independently four or five different times in human history, no more than 10,000 years ago, and probably much more recently. Because carrying one sickle cell gene conferred a survival advantage in areas of the world where malaria was common, the sickle cell mutation was positively selected and passed on in those regions.

As humans migrated, the sickle cell trait spread, not by contagion, of course, but through reproduction. Population geneticists call it 'gene flow' when a gene variant like sickle cell passes from one population to another. As a result of these historical and environmental influences, sickle cell is commonly found in central and western Africa, but not Southern Africa. It is also found on the Arabian peninsula and over into India, as well as up through Turkey, Greece, Albania, Sicily and Italy and other parts of the Mediterranean basin.

Carrying the sickle cell variant of the hemoglobin gene, therefore, is a marker not of race, but of descent from people who once lived where malaria was common.

For a map showing the spread of sickle cell, click here and scroll down to the map images.

NOTE: another mutation on the same gene but at a different locus also confers resistance to malaria, and in its double form also causes a blood disease. This disease is known as thalassemia. Thalassemia is most common in parts of southern/southeastern Asia and southern Europe.


Skin Color Handout

Why do we have different skin colors? Scientists can only hypothesize at this point because the genetics of skin color is poorly understood. But we do know that skin color tends to correlate not with 'race' but with the amount of ultraviolet radiation in the environment.

People in equatorial areas of the world, where sunlight is most intense, have the darkest skin. This includes sub-Saharan African peoples; Tamils, Dravidians and others from southern India and Sri Lanka; Aborigines in Australia; and Melanesians in the South Pacific. People living in areas where sunlight is less intense, further north and south, tend to have lighter-colored skin.

Scientists don't know why this is, but they have several theories. One theory highlights the role of vitamins and natural selection. The reasoning is as follows:

Dark melanin (skin color variation is controlled by the kind and amounts of pigment in our skin called melanin) acts as a natural sunscreen, blocking ultra-violet (UV) radiation. Too much UV radiation destroys an important enzyme made under the skin called folate. If pregnant mothers don't get enough folate, their infants may be born without a full brain, spinal cord or with other neural-tube disorders. By this reasoning, anthropologist Nina Jablonski suggests that dark skin would be a selective advantage in the equatorial areas of the world because it would block more UV radiation and thus prevent the destruction of folate (see "A New Light on Skin Color" in Resources, below). Thus, darker-skinned people would be better able to survive and reproduce in these areas.

On the other hand, the body needs some UV radiation to manufacture Vitamin D under the skin. Without enough Vitamin D, humans are prone to rickets, a crippling bone disorder most common in young children. Scientists hypothesize that among groups of early humans who migrated to regions far from the equator, where there was less sunlight, those individuals with lighter skin were better able to survive and reproduce (because they could absorb enough UV radiation to produce adequate amounts of Vitamin D). Thus light skin was increasingly selected for in those areas. (Today, most of us get Vitamin D from fish oil, cereals, and fortified milk - foods not available to early humans until we developed fishing and farming technologies).

Over time, these two contrasting influences created a marked difference in the appearance of people living in areas with different amounts of UV radiation.

NOTE: Some people assume that dark melanin provides a selective advantage because it protects against skin cancer by blocking UV radiation. While dark skin does protect against skin cancer, it does NOT provide a selective advantage. That's because skin cancer doesn't usually manifest until later in life, after the childbearing years. Unless a trait affects the ability to reproduce, no natural selection will occur and traits - positive or negative - will continue to be passed down.

An alternative theory (favored by Darwin) suggests that sexual selection drove the evolution of different skin colors and the distribution of other surface traits like hair form. According to this scenario, certain cultures (for one reason or another) came to value dark skin while others valued lighter skin color pigments. Individuals with the favored appearance in a particular culture would have the most opportunities to mate and have more children, just as peacocks with the biggest tale feathers are favored by peahens and thus out-reproduce other peacocks. Over time, this skewed reproduction would result in differences between cultures that preferred different traits. The advantage to this theory is that sexual selection can spread a favored trait through a population very quickly, while natural selection works more slowly.

Now, based on the film clips, ask the class to identify and describe three characteristics of human variation that would explain why it is so difficult to classify humans into racial boxes.

The three characteristics are:

Gradual Variation. Variation of traits is generally continuous, with no clear boundaries between them. As Joseph Graves illustrates in Episode 1 (through his imaginary walk), it is impossible to say where one race ends and another begins. Because of gene flow, groups living close to each other tend to be more visibly similar, while groups far away tend to be less so. Geography is a better explanation for similarity than race.

Non-Concordance. Human variation is highly non-concordant. One trait rarely co-varies with or predicts for another. This is because most traits are influenced by different genes, and genes are inherited independently one from another. Knowing a person's skin color does not help you predict other traits, such as height, blood type, or sickle cell. As Alan Goodman says, "Skin color or eye color or hair color is not correlated with height or weight. And they're definitely not correlated with more complex traits like intelligence or athletic performance." In a nutshell, racial profiling doesn't work on a genetic level.

Within-Group vs. Between-Group Variation. Most of the world's diversity can be found in any local population. As Richard Lewontin first observed, on average, 85% of all human variants can be found within any local population, be they Swedes, Hmong or Fulani. (About 93-96% can be found on any continent, which means only about 4-7% of human variation is explained by continental divisions). In other words, as Lewontin points out in his book Human Diversity, if a neutron bomb tomorrow wiped out everyone in the world except for Nelson Mandela's Xhosa people, 85% of the world's genetic variation would still be left, though the remaining population would on average be darker skinned. Because of this huge within-group diversity, knowing an individual's purported race tells us little about his or her specific genes and traits.

ACTIVITY #5: Final Reading Assignment and Essay

As a final exercise, ask the students to read the following article about our myths and misconceptions about racial classification and its inherent subjectivity.

Jonathan Marks, "Scientific and Folk Ideas About Heredity."

They may also want to read the "Go Deeper" article in the Sorting People section of the RACE web site.

As a culminating activity, ask students to write an essay addressing the following questions (this essay will be used for assessment):

Consider this conventional definition of race: "The idea of race assumes humans come divided into several distinct groups, each of which carry a set of innate traits. Those who are members of one race are more genetically similar to each other, and more different from members of another race."

Is this definition scientifically sound given the results from the student activity, the film clips and the readings? Why or why not? What basic scientific criteria have to be met for this definition to work? Have your ideas about race been changed by this exercise? Explain.


Students can be evaluated based on their participation in class exercises, the thoroughness of their research and analysis, and their final essay. The essay should be judged according to how well students use evidence from the exercise, the film, and background readings to support their positions.


  1. 1. Read Stephen Jay Gould, "The Geometer of Race." Discover Magazine (November, 1994). Gould tells the fascinating story of how white people came to be named after a mountain range in Georgia, and how German naturalist Freidrich Blumenbach's visual model of five races became popularized and inadvertently fueled notions of racial superiority and inferiority.

  2. Students can explore human genetic diversity further using the Cold Spring Harbor Laboratories computer exercise titled "How Unique Are You?" This exercise will calculate how many other students, out of thousands that have participated in this exercise, have the same genetic profile that they do. Don't be surprised if the answer is zero. Go to the DNAI Web site ( and navigate to the activity by clicking on Human Origins, then Variation, then Interactive Variation Activity.

  3. Explore or discuss in class the related essay taken from the "Go Deeper" article associated with the "Sorting People" section of the RACE Web site. Also read the Background Reading on the history of the Census:

    Should We Classify?

    Following are the U.S. federal government's current definitions for the racial and ethnic groups we used in the sorting activity:

    • American Indian or Alaskan Native. A person having origins in any of the original peoples of North and South America (including Central America), and who maintains tribal affiliation or community recognition.
    • Asian. A person having origins in any of the original peoples of the Far East, Southeast Asia, the Indian subcontinent including, for example, Cambodia, China, India, Japan, Korea, Malaysia, Pakistan, the Philippine Islands, Thailand, and Vietnam.
    • Black or African American. A person having origins in any of the black racial groups of Africa. Terms such as "Haitian" or "Negro" can be used in addition to "Black or African American."
    • Hispanic or Latino. A person of Cuban, Mexican, Puerto Rican, South or Central American, or other Spanish culture of origin, regardless of race. The term "Spanish origin" can be used in addition to "Hispanic or Latino."
    • Native Hawaiian or Other Pacific Islander. A person having origins in any of the original peoples of Hawaii, Guam, Samoa, or other Pacific Islands. White. A person having origins in any of the original peoples of Europe, the Middle East, or North Africa.

    Most of these categories were introduced in 1977, in response to new civil rights laws designed to remedy discrimination. Look closely at these definitions. Is everybody defined in the same way? To be categorized as Native American, for example, requires "tribal affiliation or community recognition" - a condition of no other category. The definition for African American includes a reference to "black racial groups" while none of the other categories mention race. In fact, Hispanic or Latino is defined as a "Spanish culture of origin, regardless of race." The category Native Hawaiian or Other Pacific Islander was only introduced in 1996 - previously, it was lumped together with Asians.

    What reasons might exist for defining these groups in these seemingly contradictory ways? Are the criteria social or scientific?

Even though there's no consistently objective way to classify people, can you think of reasons why we would want the government to categorize or track information on racial groups? What would happen to efforts to remedy discrimination and inequality if we didn't have any racial data?


RACE Web Site:

Richard Lewontin, Human Diversity, Scientific American Library, 1982, 1995

Stephen Jay Gould, The Mismeasure of Man, W.W. Norton, 1981, 1996

Saadia Iqbal, "A New Light On Skin Color," National Geographic Magazine Online. (

DNA From the Beginning (

DNAi Web site: (


From Mid-Continent Research for Learning and Education at

Nature of Science Standard 11 Level IV (Grades 9-12):

  1. Knows ways in which science distinguishes itself from other ways of knowing and from other bodies of knowledge (e.g., use of empirical standards, logical arguments, skepticism)
  2. Knows that scientific explanations must meet certain criteria to be considered valid (e.g., they must be consistent with experimental and observational evidence about nature, make accurate predictions about systems being studied, be logical, respect the rules of evidence, be open to criticism, report methods and procedures, make a commitment to making knowledge public)
  3. Understands how scientific knowledge changes and accumulates over time (e.g., all scientific knowledge is subject to change as new evidence becomes available; some scientific ideas are incomplete and opportunity exists in these areas for new advances; theories are continually tested, revised, and occasionally discarded)
  4. Knows that from time to time, major shifts occur in the scientific view of how the world works, but usually the changes that take place in the body of scientific knowledge are small modifications of prior knowledge



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