1. Humans use negative pressure to fill the lungs, and frogs use positive pressure.
a. What is the difference between negative and positive pressure?
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b. Birds have a flow-through system-the air flows from the lungs into air sacs and then out by way of a separate set of tubes. In what way is this more efficient than human breathing?
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c. Frogs have thin, moist skin, and reptiles have thick skin. Which animal do you predict practices skin breathing? Which animal most likely has better developed lungs?
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d. Humans have a diaphragm, reptiles do not. In what way does a diaphragm assist breathing?
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2. Refer to Figure 31.16 to answer the following questions.
a. What might have caused the evolution of the upright posture of A. afarensis?
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b. How does the hominid evolutionary tree illustrate adaptive radiation?
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c. How does the evolution of Homo erectus and Cro-Magnon support the concept of punctuated equilibrium?
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d. How do you know that all human races should be considered the same species?
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