Investigating Common Descent: Formulating Explanations and Models
Pre-Activity Question: Did humans evolve from apes? (YES or NO) _________
What is the difference between these two questions?
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Question #1: Did humans evolve from modern apes?
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Question #2: Do modern apes and humans have a common ancestor?
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Gibbons, chimpanzees, gorillas, and orangutans are four groups included in the ape family.
APES
African
Asian
Gorilla
Gibbon
Chimpanzee
Orangutan
Chimps and gorillas represent the African side of the family; gibbons and orangutans represent
the Asian side of the family. We will only focus on the African side of the family in the
following activity.
Analyzing a Morphological Tree for Common Ancestry
Morphological tree:
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Illustrated relationships among organisms
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Is based on comparisons of skulls, jaws, skeletons, and other structures
Find the part of the morphological tree that shows the relationships between gorillas, chimpanzees, and humans
(No lines showing relationships). Work with your partner and develop a hypothesis to explain how these organisms
are related.
Make a diagram of your hypotheses by drawing lines from Point A to each of the three organisms: G
= gorilla, C = chimpanzee, H = human, A = common ancestor.
Hypothesis:
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DNA as Evidence of Evolution
Modern research techniques allow biologists to compare the DNA that codes for certain proteins and to make
predictions about the relatedness of the organisms from which they took the DNA.
Purpose: To test the hypothesis you developed in the previous section (morphological trees).
Procedure: Observe the strands of DNA from a human, chimpanzee, gorilla, and the common ancestor. These
strands represent a small section of the gene that codes for the hemoglobin protein (the protein found in the red
blood cells of all these organisms that allows your red blood cells to carry oxygen). Complete the following tables.
Hemoglobin Gene Hybridization Data for Human DNA
Human DNA compared to:
Number of matches
Unmatched bases
Chimpanzee DNA
Gorilla DNA
1. How do the gorilla DNA and the chimpanzee DNA compare with the human DNA?
2. What do these suggest about the relationship between humans, gorillas, and chimpanzees?
3. Do the data support any of your hypothesis? Explain why or why not.
4. What kind of data might provide additional support for your hypothesis?
Hemoglobin Gene Hybridization Data for Common Ancestor
Common Ancestor DNA compared
to:
Number of matches
Unmatched bases
Human DNA
Chimpanzee DNA
Gorilla DNA
5. Which DNA is most similar to the common ancestor DNA? ________________________________
6. Which two DNA’s were most similar in the way they compared to the common
ancestor?______________________________ and ___________________________________
7. Do your findings prove that this hypothesis is correct? Why or why not?
8. Based on the data, which of the following statements is most accurate? Explain your answer in a short
paragraph.
a) Human and apes have a common ancestor
b) Humans evolved from apes
9. A comparison of many more DNA sequences indicates that human DNA and chimpanzee DNA are 98.8 percent
identical. What parts of your data support this result?