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Ch. 22 - Descent with Modification: A Darwininan View of Life
Chapter 22, Problem 7

A swim bladder is a gas-filled sac that helps fish maintain buoyancy. The evolution of the swim bladder from the air-breathing organ (a simple lung) of an ancestral fish is an example of a. exaptation. b. changes in Hox gene expression. c. paedomorphosis. d. adaptive radiation.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Exaptation

Exaptation refers to a trait that originally evolved for one function but later became useful for a different purpose. In the case of the swim bladder, it evolved from an ancestral lung, initially serving respiration, and later adapted to help fish with buoyancy. This concept highlights how evolutionary processes can repurpose existing structures for new functions.
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Hox Gene Expression

Hox genes are a group of related genes that control the body plan of an embryo along the head-tail axis. Changes in Hox gene expression can lead to significant morphological changes in organisms. While Hox genes play a crucial role in development, they are not directly related to the evolution of the swim bladder from lungs, making this concept less relevant to the question.
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Adaptive Radiation

Adaptive radiation is the process by which organisms diversify rapidly into a wide variety of forms to adapt to different environments. This concept explains how species evolve to fill various ecological niches. Although it is a significant evolutionary mechanism, it does not specifically address the transition of the swim bladder from a lung, which is more accurately described by exaptation.
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Related Practice
Textbook Question

Within six months of effectively using methicillin to treat S. aureus infections in a community, all new S. aureus infections were caused by MRSA. How can this best be explained? a. A patient must have become infected with MRSA from another community. b. In response to the drug, S. aureus began making drug- resistant versions of the protein targeted by the drug. c. Some drug-resistant bacteria were present at the start of treatment, and natural selection increased their frequency. d. S. aureus evolved to resist vaccines.

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Textbook Question

DNA sequences in many human genes are very similar to the sequences of corresponding genes in chimpanzees. The most likely explanation for this result is that a. humans and chimpanzees share a relatively recent common ancestor. b. humans evolved from chimpanzees. c. chimpanzees evolved from humans. d. convergent evolution led to the DNA similarities.

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Textbook Question

The upper forelimbs of humans and bats have fairly similar skeletal structures, whereas the corresponding bones in whales have very different shapes and proportions. However, genetic data suggest that all three kinds of organisms diverged from a common ancestor at about the same time. Which of the following is the most likely explanation for these data? a. Forelimb evolution was adaptive in people and bats, but not in whales. b. Natural selection in an aquatic environment resulted in significant changes to whale forelimb anatomy. c. Genes mutate faster in whales than in humans or bats. d. Whales are not properly classified as mammals.

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