“Who is Who’s Best Friend?” Evolution of the Dog Case Study 2

Unit 2- Natural Selection, Evolution and Change Over Time

Please answer the questions (A, B, C and D) on a separate sheet of paper.

Introduction:

Where did the dog come from? If you look at the hypothetical family tree shown here, you can see that the canine group began evolving about 30 million years ago from a tiny tree climbing animal, Miacis. The dog appears to be the first animal domesticated by humans. DNA evidence indicates that dogs were initially domesticated from wolves about 100,000 years ago. Tribes used dogs for help with hunting, for protection at night, and for companionship. After dogs were domesticated, they were selectively bred for particular characteristics. Just as other domesticated animals have been bred, dogs were bred so that they had the characteristics most desired by humans. In different parts of the world, the choice of desirable characteristics varied, resulting in the diversity we see today. As dogs continued to live as human companions, many new breeds were developed for specific tasks, such as hunting, guarding, working, and companionship. The basic principles of dog breeding are those that apply to any animal. Breeding pairs are selected for the desirable genes they will pass on. Some characteristics involve single-gene inheritance. However, many characteristics, such as coat color, depend on more than one gene. A cross between two heterozygous parents can produce a puppy with blue eyes even though both parents have brown eyes. In German Shepherds, the alleles for white fur and dark eyes are recessive. Two black or two tan parent dogs can still produce a white puppy.

Objectives: By the end of this case study, you will be able to…

• Understand how natural selection can act on a population to cause speciation.

• interpret phylogenetic diagrams.

• Distinguish between natural selection and artificial selection events.

Case Study: Read the story below. Answer the questions that follow about early relationships between human and wolf.

A young boy is sitting near the edge of a cave 20,000 years ago. He has just taken out the garbage from the group’s previous day’s activities. The garbage consists of mostly bones and scraps of food from a recent successful hunt. As dusk approaches, the wolves start to arrive. The boy is not frightened. He has seen the wolves many times before. In fact, their arrival is almost ritualistic. They move in from the forest and wait until all the humans have gone into the cave for the night. The boy notices that the same wolf is the first one to get to the good scraps. It doesn’t immediately run off when it sees the boy.

Part A: Recognize and Recall.

1.  Describe how natural selection illustrates why wolves not fearful of people are more fit in this environment.

2.  How would the wolf pups inherit the selective factor of lack of fear towards humans?

3.  Why would or would not the transformation from ancient wolf in the story to domesticated dog happen quickly?

Part B: Interpret, Classify, Infer and Explain.

Look at the phlyogenetic tree and the notes below of the molecular evolution of the dog family.

4.  According to the diagram, what is closest living common ancestor of the Domesticated Dog? How can you tell from the phylogenetic tree?

5.  How was this phlyogenetic tree made? Why is this a better method of categorizing relationships than grouping by common physical characteristics?

6.  What does the “?” from the Red Wolf mean? Why do you think (via natural selection) that Red Wolves have not fully speciated from Gray wolves or Coyotes?

Part C: Apply and Analyze.

On Monday in class, we will view the film Dogs and More Dogs, a PBS NOVA presentation. The video investigates how and why man’s best friend evolved from wolves, and why dogs are so remarkably diverse today. As you watch the film, jot down ideas to help you answer the question that follows. (A transcript of the movie is available on my webpage!)

a.  Discuss the two possible explanations (adoption / adaptation) for the evolution of dogs.

b.  Cite reasons for each explanation.

c.  Which hypothesis do you support? Why?

Part D: Evaluate and Create.

Dogs and humans have benefitted from their close and personal relationship throughout history. Now, they are helping us understand ourselves by studying genetic diseases in dogs. We are able to develop genetic tests to identify diseases in dogs and to gain insight into human genetic diseases.

a.  Research a disease that is studied in dogs that affects humans. Name the disease and give its cause and symptoms.

b.  Explain why dogs make good models for studying human disease.

c.  Give your opinion: Is this an ethical practice? Have we irrevocably hurt our “best friends” through artificial selection, selective breeding and inbreeding?

Source: Not Necessarily on Purpose: Domestication and Speciation in the Canidae Family by Tom Horvath

Department of Biology at SUNY College at Oneonta

Available online at http://sciencecases.lib.buffalo.edu/cs/collection/detail.asp?case_id=477&id=477