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? Question #1: Did humans evolve from modern apes? 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.

APESAfrican Asian

Gorilla Gibbon

ChimpanzeeOrangutan

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 AncestryMorphological tree:

Illustrated relationships among organisms 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: ___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

DNA as Evidence of EvolutionModern 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 DNAHuman DNA compared

to:Number of matches Unmatched bases

Chimpanzee DNAGorilla 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?

PigDonkeyHorse

Dog

RodentRabbitRhesus monkeyGibbon

AGorillaChimpanzeeHuman

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 AncestorCommon Ancestor DNA

compared to: Number of matches Unmatched basesHuman DNA

Chimpanzee DNAGorilla 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 ancestorb) 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?