The data lend support to the hypothesis that the chimpanzee is more closely related to humans than the gorilla is.

  1. What kinds of data might provide additional support for your hypotheses?

    The students could test the hypotheses using additional data from DNA sequences or morphological features. They also could gather data from the fossil record.    

Instructional Strategy: Part III

Begin this part by pointing out that biologists have determined that some mutations in DNA occur at a regular rate. They can use this rate as a "molecular clock" to predict when two organisms began to separate from a common ancestor. Most evolutionary biologists agree that humans, gorillas, and chimpanzees shared a common ancestor at one point in their evolutionary history. They disagree, however, on the specific relationships among these three species. In this part of the activity, you will use data from your paper-clip model to evaluate different hypotheses about the relationships between humans, gorillas, and chimpanzees.

Evolutionary biologists often disagree about the tempo of evolutionary change and about the exact nature of speciation and divergence. Reinforce the idea that models can be useful tools for testing hypotheses.

Procedure Step 1. Assume that the common ancestor DNA synthesized in Part II represents a section of the hemoglobin gene of a hypothetical common ancestor. Compare this common ancestor DNA to all three samples of DNA (gorilla, human, and chimpanzee), one sample at a time. Record the data in a table.

The data for the comparisons are as follows: human DNA, 10 unmatched bases; chimpanzee DNA, 8 unmatched bases; gorilla DNA, 3 unmatched bases.

Evaluate

  1. Which DNA is most similar to the common-ancestor DNA?  

    Gorilla DNA is most similar to the common-ancestor DNA.

  2. Which two DNAs were most similar in the way that they compared to the common-ancestor DNA?  

    Human DNA and chimpanzee DNA have similar patterns when compared to the common ancestor DNA.

  3. Which of the hypotheses developed in Part I do your data best support?  

    Answers will vary.

  4. Do your findings prove that this hypothesis is correct? Why or why not?  

    Data from the models do not prove the validity of a hypothesis, but they do provide some direction for additional research.

  5. Based on the hypothesis that your data best supported, which of the following statements is most accurate? Explain your answer in a short paragraph.  

    1. Humans and apes have a common ancestor.  

    2. Humans evolved from apes.  

  1. The students should infer that humans and apes share a common ancestor, represented by a common branching point.

  1. According to all the data collected, which of the following statements is most accurate? Explain your answer in a short paragraph.  

    1. Chimpanzees and humans have a common ancestor.  

    2. Chimpanzees are the direct ancestors of humans.  

  1. The students should infer that chimpanzees and humans share a common ancestor and that modern chimpanzees are not the direct ancestors of humans.

  1. 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?

    The morphological tree and the DNA comparison data indicate that humans are closely related to chimpanzees.

  2. What methods of science did you use in this activity?

    Many answers are possible, including making observations, forming and testing hypotheses, and modeling.



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