Name: ______________________
Group: ____________________
Human Variation Reading and Quantifying Human Skin Color Using ADI
Part A: Background Reading: Humans-- we are more similar than different
If you look around, you see a lot of variation in the way people look. However, humans are WAY MORE SIMILAR
than they look. First of all, all humans have 23 pairs (a pair = 2) of chromosomes, for a total of 46 chromosomes. This
means humans are all the same species. Scientists claim that 99.9% of all human’s DNA is exactly the same between
people who may look very different from each other. All humans can trace their most distant ancestors back to Africa.
Because of that, humans are all related. Mathematicians have determined that everyone on the planet is at most 50th
cousins of each other! Most of the DNA in people has gene codes that say make a human, not a fish or a bacterium or a
tree. A very small fraction of the DNA code (.01% ) creates many of the visible traits that we notice as the variation we
see in people: different hair color, hair texture, eye color and skin color.
The diagram above shows real human chromosomes. There are 23 pairs of them. One of the chromosomes in each pair
comes from a person’s mother. The other chromosome in the pair comes from a person’s father. Sections of
chromosomes, called genes, are what control traits. Notice that the person has two X chromosomes so they are female.
If the person had an X chromosome and a Y chromosome, the person would be a male.
Part B: Human Variation—Your very own DNA!
If people have nearly the same DNA, why do they look so different? Each person has their very own DNA code
(except identical twins which have EXACTLY THE SAME DNA). You have your own code which is a unique combination of
genes which you got from your mother and father. Your mother and father got a unique combination from their
parents! So, every person has their own DNA and their DNA is slightly different from some else’s DNA. Your DNA is so
unique, that, if someone finds just one of your cells and takes the DNA out, the code can be read and it proves that the
DNA is yours! This proof is better than your fingerprint! This is because EVERY ONE OF YOUR CELLS has all of your own
unique DNA code in it. You could (in theory) take the nucleus out of one of your skin cells, put it inside another cell (an
egg cell that has its nucleus removed) and create an entire whole other you… a clone!!
The way that people end up looking different from one another happens in one of three ways: genes from
parents combine in different ways (usually), changes in the DNA code (mutations) create new traits (less common), or
babies have more or less chromosomes than they should (very rarely). With chromosomes and DNA, more is not
better. Notice that the person below has 3 chromosomes on number 21. Usually, there are 2—one from the mother
and one from the father. Because this person has 3 chromosomes on 21, they have Down’s Syndrome. Can you tell
what gender they are by looking at the chromosomes, not the picture?
Part C: Human Variation and Human Groups—The Good, The Bad and The Ugly
Human variation is based on different DNA codes. But, grouping people into broad categories like Black, White,
and Asian is not based on DNA. Human groups are made up by humans for a variety of reasons. In fact, it is believed
that the notion of black, white and Asian originated in Europe in the 1800’s as a way to distinguish Europeans (whites)
from other people.
If you consider racial groupings based on skin color, you will see that there are many problems with classifying
people this way. Let’s take the groups, “black and white.” We have all heard people either identify as black or white or
refer to another person as black or white. However, there is no such thing as pure black skin or pure white skin. In fact,
every person has varying shades of brown pigment in their skin. There is no actual point at which everyone would agree
that a person would be called black or white based only on skin color. Also, a person who might be called black in the
United States may not be called black in Brazil. A person who might be called white in the United States might not be
called white in Norway.
People have varying shades of brown skin based on how much melanin (brown skin pigment) their genes
produce. Additionally, people have other skin pigments such as carotene (which is yellow). The color of a person’ skin is
related to where their ancestors came from. Remember that the reason why you are here is that the people that came
before you had to have been winners! You are the product of many, many generations of people who survived! And, if
you go way back (before sunscreen and lots of clothing), a major determinant of survival or not was skin color. Melanin
protects skin from the harmful rays of the sun which can go into skin cells and cause a change in the DNA which may
result in cancer. However, some amount of sun is needed to keep people healthy! Sun rays are needed because your
body makes vitamin D when you are in the sun. Vitamin D is necessary for strong bones! Sunlight is also associated
with a chemical called folic acid which is needed for healthy babies. So, everyone’s skin needs to let sunlight in and it
does! This is why there is no such thing as pure black skin. Pure black skin would not let sun in and people would have
weak bones and unhealthy babies and we know this is not true. On the flip side, there is no thing as pure white skin,
except for people who are albinos. This is because pure white skin would have no melanin in it which protects the skin
from the harmful rays of the sun which can cause DNA damage and skin cancer.
So a person’s particular shade of brown skin depends on where a person’s ancestors came from. People who
migrated out of Africa and lived along the equator tended to have darker brown skin (for health reasons) than people
who migrated out of Africa and went to areas where the sun was less intense. If you were to walk from the equator to
the North Pole, you would see this. In general, people’s skin goes from dark brown to light brown as you go farther from
the equator. However, on your walk there would be no point at which you would say you have walked from the black
people to the white people.
In spite of people’s inability to actually measure traits, like skin color, people continue to group people by them
and there are advantages and disadvantages to doing so. The good thing about grouping people is that people can feel
part of a group and have a group identity and a shared culture. However, grouping people may not always be a good
idea. Because groups are made by people, they change over time and place. In the U.S., Irish used to be called a race
and so did Italians. They would now be considered “white.” A person who is considered to be “black” in the U.S. may
not be considered “black” in Haiti. Also, not every person identifies with a group and there are not groups for everyone.
Additionally, within a group, there is a lot of variety of people. There are a lot of different kinds of people who would be
classified as either Asian, White or Black. Grouping people can lead to stereotypes (either positive or negative) about
people rather than considering individual people. When there are race and ethnic groups, some people may pre-judge
someone based on the group they are in. Sometimes the pre-judging is positive as in some people generalize and say
“Asians are good in math.” Sometimes the pre-judging is not positive as in “white people can’t jump.”
Putting people in groups can also lead to some very bad things. Grouping people enables some people to claim
they are in a superior group and justify (to themselves) treating another group poorly, as in denying people jobs or
access to health care and education. In the worst cases, one group can feel superior enough to enslave another group of
people or even rationalize killing another group of people (as in the Holocaust and other instances of genocide).
In summary, every human is unique but also nearly the same as every other human. Humans are all one species
whose ancestors originated in Africa. Putting people into groups is not based on DNA. There is natural variation in the
color of human skin. However, there is no such thing as pure white skin or pure black skin. The notion that there are
black, white, yellow and red skinned people is one that was made up by people to classify them and is not based on
biology. In this activity, you will investigate skin color and see the variety of colors that make up the varying shades of
brown skin that we see around the world.
Part D: Mixing Light—Color Basics
1. Review the major concepts of mixing light vs pigment in the Color Basics software. Remember: black is 0%
intensity for all R, G, B values. White is 100% intensity for all R, G, B values
Part E: Quantifying Human Skin Color Using ADI software
1. Use a marker to make a 1 cm square on the underside of your forearm. Try to make the square on an area of
skin that DOES NOT have an obvious blood vessel running through it.
2. Take a picture of the area of skin just inside the square and analyze the color in it using ADI. Record the R, G, B
values in a data table.
3. Repeat steps 1 and 2 with other people. Aim to get a variety of people from various racial and ethnic groupings.
See if you can get images of people who identify as being either “black,” “white,” Asian (“yellow”), Latino, or
Native American (“red”).
4. Summarize the data from your table in a paragraph and explain what you have learned about variation in human
skin color based on this lab.
5. Can you say that anyone that you sampled has either black, white, red or yellow skin? Use data to support your
answer.
Part F: Sample Data Table
Participant Number
1
Self-Described Racial/Ethnic
Group
White
ADI values from the forearm skin photo
R:
R:
R:
R:
R:
R:
R:
71
G: 63
G:
G:
G:
G:
G:
G:
B: 73
B:
B:
B:
B:
B:
B:
Average: 69
Average:
Average:
Average:
Average:
Average:
Average: