Dog Variety

Podcast

Dog Variety

Transcript

The truth about cats and dogs. I'm Bob Hirshon and this is Science Update.

Compare a cute little Chihuahua to a hulking St. Bernard, and it might be hard to believe they're the same species. Traci Watson of Washington, DC, noticed this, and asked us why cats don't show the same variety in size and shape.

Well, Traci, we consulted Jasper Rine, a geneticist at the University of California at Berkeley.

Rine:
Your listener raises a very interesting question about what happened to cats. No creature has changed so much through its interactions with humans as dogs, nor as little through its interactions with humans as cats. And that really is an interesting question.

Dr. Rine says no one really knows the answer to that question, but he speculates that dogs were bred more extensively than cats. People wanted dogs with useful traits, such as speed for racing or hunting, or strength for pulling a sled. Cats, though, were bred mostly for their appearance.

Rine:
And hence what we end up with is cats that have some different kinds of coats and colorations, but no one has ever really tried to select for a cat that could be a draft animal or that would hunt on command.

If a science question is dogging you, call us at 1-800-WHY-ISIT. If we use it on the show you'll get a free Science Update mug. For the American Association For The Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

Dogs come in a mind-boggling range of sizes, from tiny ones that fit in your handbag to those that can practically be saddled up like a horse. Strangely, cats don't seem to show the same level of diversity. This Science Update explores how selective breeding - selecting individuals that have a desirable trait and breeding them - will eventually get the population average of a species moving in the direction you've chosen. It also attempts to explain why dogs, more than any other domesticated animal, demonstrate such remarkable differences in size and shape. Researchers are mapping the dog genome to identify the slight genetic variations that account for these differences. Through this research they are also identifying the genes responsible for inherited diseases in dogs, in the hopes of one day eliminating the threat of these illnesses.

As you read or listen to the transcript for this Science Update, and explore the websites below, keep in mind the following questions:

1. What accounts for the vast diversity in the shapes and sizes of dogs?
2. What breeds of dog would you think were bred for appearance? for hunting? for work (sled dogs, rescue dogs, guard dogs, seeing eye dogs, etc.)? What other characteristics or behaviors do you think dogs have been bred for?
   
3. Why don't cats demonstrate the same level of diversity?
4. What other domesticated animals show a high level of diversity?
5. How would a population average of a species in the wild move toward a particular trait?
6. Can you think of examples of plants that have been selectively bred for a particular trait?

Going Further

To learn more about Dr. Rine's work, go to The Rine Lab website.

Younger students can visit Choosing a Dog: Purebred Basics from AnimalPlanet.com to see different categories of purebred dogs, and the characteristics and behaviors for which they are bred.

To explore how a lack of genetic diversity can impact a species' survival, go to the Science NetLinks lesson for grades 9-12 entitled Genetic Diversity. Using the example of a cheetah, students investigate how heritable characteristics can influence an organism's ability to survive and reproduce.