Whether you like your cats striped or spotted, sleek or fuzzy, there is a breed for you. Indeed, cat breeding has become a multi-billion dollar business around the world, with breeders constantly competing to create exotic new varieties that might win the blue ribbon at the next pet show. Often, cat breeders will carefully comb wild and domestic breeds looking for just the right combination of characteristics, matching long hair from one breed, for example, with racy stripes from another. But other times, chance plays as big a role as design in the development of a popular breed.

The remarkable curve-eared American Curl, for instance, got its start with a stray cat discovered in California in 1981. “On a sunny day in June, a longhair silky black female kitten with unusual ears wandered up to the doorstep of Joe and Grace Ruga,” explains one Web site devoted to the cats with the gracefully-arced ears. “Joe [asked] Grace not to feed the kitten. Grace, not abiding by her husband’s wishes but listening to her heart instead, left a bowl of food on the porch. The affectionate black kitten quickly worked her way into the Rugas’ hearts (especially Joe’s) and they named her Shulamith, which means “black but comely.” Such are the beginnings of the American Curl as it is known today.

Like other breeds, the American Curl is officially registered as a breed with one of the several associations that keeps track of new varieties. The associations help define what makes a champion show cat. For the American Curl, for instance, the degree of curl to the ear is a key factor. Tufts of ear fur — called “furnishings” — and plumed tails are also considered handsome additions. The Curl, however, is just one of the thousands of cat breeds that people have created over time. And at Wild Side Exotics, a consortium of feline breeders in California, the search for new breeds continues. Using domesticated descendants from some of the 28 species of wild small cats, the breeders aim to produce “beautiful, elegant, hybrid felines with the exotic looks of their wild heritage and the predictable temperaments of domestic cats.”

Current offerings include such exotic-sounding and -appearing breeds as the Asian leopard cat, or Bengal, sporting leopard spots and rosettes or marbled pelts. Some have “glittered” coats, meaning the fur includes strands of shimmering and glistening hair. Savannahs are another striking breed, with golden black-spotted coats, long legs and neck, and large ears.

Given the work that goes into creating these breeds, it’s not surprising that the cats don’t come cheap. Even a homely kitten of uncertain quality can cost more than $400 — with especially unusual varieties reaching $3,500 or more. These custom-bred cats’ values have led some owners to begin looking for new ways to safeguard their treasured pets from catnappers, who can make big gains reselling their victims on the pet black market. One possibility that some researchers have suggested is taking a cat’s noseprint. Like fingerprints, it appears that the skin on every cat’s nose “leather” has its own unique pattern. So far, however, few owners have taken up the idea. The prospect of ending up with an angry, hissing, spitting, and smudge-nosed cat on their scratched-up hands seems to be too much effort for too little reward.

To order a copy of EXTRAORDINARY CATS, please visit the NATURE Shop.
Online content for EXTRAORDINARY CATS was originally posted February 1999.

In the same way that inbreeding among human populations can increase the frequency of normally rare genes that cause diseases, the selective breeding that created the hundreds of modern dog breeds has put purebred dogs at risk for a large number of health problems, affecting both body and behavior.

Some conditions are directly related to the features breeders have sought to perpetuate among their dogs. As they deliberately manipulated the appearance of dogs to create or accentuate physical characteristics that were considered aesthetically pleasing, like the flat face of a bulldog or low-slung eyelids of a Bloodhound, breeders also created physical disabilities. The excessively wrinkled skin of the Chinese Shar-Pei causes frequent skin infection; Bulldogs and other flat-faced (or brachycephalic) breeds such as the Pekingese have breathing problems because of their set-back noses and shortened air passages; Bloodhounds suffer chronic eye irritation and infection.

The unnaturally large and small sizes of other breeds encourage different problems. For example, toy and miniature breeds often suffer from dislocating kneecaps and heart problems are more common among small dogs. Giant dogs such as Mastiffs, Saint Bernards, and Great Danes are nearly too big for their own good. Researchers have found a striking correlation between a dog’s large size and a frequency of orthopedic problems like hip dysplasia. Large dogs are often prone to heat prostration because they can’t cool down their bodies (tiny dogs, by contrast, have a hard time staying warm), and because of the massive weight they must support, these breeds are prone to malignant bone tumors in their legs. Meanwhile, the huge head and narrow hips of the Bulldog can necessitate that their pups must be born by Caesarean section.

Other health problems among purebreds are the product of both inbreeding and bad genetic luck. The genes responsible for many genetic diseases are “recessive,” which means that two copies of a damaged gene, one from the mother and one from the father, must be present in an individual for the disease to occur. Individuals that carry only one copy of the disease gene don’t have the condition, and are carriers of the disease. Normally, because disease genes are relatively rare, it is unlikely that both the mother and the father will be carriers, and even less likely that they’ll both give the disease gene to their offspring. But that’s not the case for purebred dog breeds, where genetically similar individuals are intentionally mated, increasing the concentration of disease genes. It’s like stacking a deck of cards with ten extra aces and ten extra face cards; the loaded deck increases your chance of hitting blackjack in a game of 21-but what you “win” might be allergies or a predisposition to cancer.

Bloodhounds suffer chronic eye irritation and infection.

Skin problems

A skin allergy, atopic dermatitis, inflicts itchy, inflamed skin on as many as 15 percent of all dogs, but certain breeds are particularly susceptible. Dog breeds prone to atopic dermatitis include Dalmatians, Vizslas, and several terriers, such as the Boston Terrier, Bull Terrier, and the West Highland White Terrier. The numerous skin folds of a Chinese Shar-Pei, so valued by some breeders, can become breeding grounds for staphylococcus and other bacteria, which cause frequent skin infections. Also, excess wrinkles of skin on the face can rub on the eye, causing lesions and, potentially, blindness.

Immune system disease

In autoimmune disorders, an individual’s immune system, which normally works to fight off foreign invaders, launches a misguided attack against its own tissues and cells. A number of inherited diseases compromising the immune system have been noted in dogs, including primary severe combined immunodeficiency (a dog version of the “bubble boy” disease) among Basset hounds, Cardigan Welsh Corgis, and Dachshunds. Addison’s disease, an autoimmune disease that affects the hormone-producing adrenal glands, occurs more frequently among several particular breeds, including the Bearded Collie, Portuguese Water Dog, and Standard Poodles. Diabetes mellitus, an autoimmune disorder affecting the body’s response to sugars, shows up more frequently among Samoyeds and Australian Terrier dogs.

Blood disorders

Bassett Hounds are prone to an inherited abnormality the effects the ability of the platelets in the blood to clump together after an injury. The blood doesn’t clot properly, leading to hemorrhage and bruising. Clotting problems also plague dogs with von Willebrand’s disease, a genetic condition frequent in Doberman Pinschers.

Neurological, behavioral, and sensory

Neurological and behavioral problems afflict many pure breeds. Bull Terriers, for example, often compulsively chase their tails. Pugs are be predisposed to Pug Dog encephalitis, a fatal brain disease. Scottish Terriers are affected by Scottie Cramp, a disorder that causes the dogs to lose muscle control when they get excited. German Shepherds may inherit degenerative myelopathy, a crippling spinal cord disease that causes weakness and eventually paralysis.

Hearing and vision

Hereditary hearing loss is common in Dalmatians, Australian Cattle Dogs, and English Setters. Alaskan Malamutes, Siberian Huskies, Samoyeds, Bichon Frise, and more than 60 other purebred dogs suffer from inherited forms of cataracts, while progressive retinal atrophy, a common cause of blindness in purebreds, is particularly a problem in Old English Sheepdogs and Papillons.

Heart disease

Sudden death from cardiac disease is recurrent in several dog breeds, including Doberman Pinschers, Great Danes, Irish Wolfhounds, and German Shepherds. Boxers can be genetically predisposed to an irregular heartbeat. High blood pressure afflicts many small breeds including Poodles, Cocker Spaniels, Staffordshire terriers, among others.

Other organs and systems

Low thyroid function crops up most frequently in Alaskan Malamutes, English Setters, Golden Retrievers, Keeshonds, Samoyeds, and Siberian Huskies. Gastric torsion, or bloat, a potentially life-threatening inability to expel gas from the digestive system, is common among deep-chested breeds such as the Great Dane, Doberman, and German Shepherd. An inherited form of kidney disease affects English Cocker Spaniels, while Dalmatians are prone to kidney stones and Basenjis suffer from Fanconi Syndrome, a potentially fatal inherited disease in which the kidneys fail to reabsorb nutrients. Liver damage and cirrhosis are common in Bedlington Terriers because of an inherited condition called copper toxicosis, in which high levels of copper accumulate in the liver.

Cancer

Cancers are strongly influenced by genetics, and so it is not surprising to find various types of cancer among different dog breeds. For example, bone cancer, or osteosarcoma, is considerably more frequent among large and giant breeds of dogs, such as the Irish Wolfhound, Great Dane, Rottweiler, Labrador and Golden Retriever, Greyhound, and Saint Bernard, because their bones are stressed by carrying so much weight. High rates of malignant blood vessel tumors are seen among Golden Retrievers, which are also prone to leukemia and brain tumors. German Shepherd Dogs and Chow Chows are predisposed to gastric cancer, while Scottish Terriers are 18 times more likely to develop bladder cancer than are other breeds.

Orthopedic

Hip dysplasia, in which looseness in the hip joint causes excessive wear that eventually leads to arthritis, is most common among large dogs, especially those like the German Shepherd Dog and the Saint Bernard which have heavy, broad hips. The long neck and large head of breeds such as the Great Dane and the Doberman can cause the compression of the spinal cord in neck vertebrae, leading to wobbling and falling (”wobbler syndrome”). Selective breeding of the disproportionately short legs of breeds such as the Basset Hound and the Dachshund has led to bowed legs and chronic problems with elbow dislocation; the short legs and long back of Dachshunds causes them to suffer more often from ruptured vertebral disks. Because of their small bones, toy and miniature breeds are more likely to experience patellar luxation, the slipping or dislocation of the kneecaps.

Background:
Cattle originally evolved over millions of years through a process of natural selection-also known as “survival of the fittest”-which made them adaptable to a wide variety of environments, including most of those inhabited by another highly adaptable species: humans. Once humans discovered how to domesticate cattle about 4,000 years ago, they began to selectively, or “artificially,” breed them for specific desired traits like meat and milk production. This resulted in animals fit less for survival in the wild than the satisfaction of human needs, but in purely genetic terms, the arrangement has proven highly successful for cattle. Cattle now thrive throughout the world in over 800 different breeds, each more or less successfully adapted to their environment and the needs of their human caretakers.

The excerpted clips from the NATURE episode “Holy Cow!” illustrate some of the naturally evolved and artificially selected attributes of cattle.

Suggested Focus Questions:

Clip 1: A Cow’s Digestive System

1. What role do microbes serve in a cow’s rumen?
2. Does this clip illustrate naturally or artificially selected attributes?
3. Why would a cow’s ability to eat grass make it ideal for human domestication?

Clip 2: Desirable Breeding Traits in Cattle

1. How many different breeds of cattle have humans created?
2. Would the qualities that make good beef cattle help them survive in the wild?
3. Besides milk and meat production, what other traits might humans wish to breed in cattle?

Clip 3: Different Breeds of Cattle

1. What might indicate that a cattle breed is adapted to cold climates like Scotland?
2. What do the different breed names refer to?
3. Why might “adaptability” be a desirable trait in a specific breed?

Downloadable QuickTime versions of the video segments:
(Note: To downoad a video, right-click on the video title and click “Save Link As…” or “Save Target As…” On a Mac, press the CTRL key and simultaneously click the mouse, then save the link.)

Clip 1, “A Cow’s Digestive System”

Clip 2, “Desirable Breeding Traits in Cattle”

Clip 3, “Different Breeds of Cattle”

GRADE LEVEL: Grades 9-12

TIME ALLOTMENT: Two to three 45-minute class periods

OVERVIEW: Cattle evolved through the slow process of natural selection until human domestication, which rapidly accelerated their development as an artificially selected species fit less for survival than to satisfy human needs. This lesson focuses on how and why humans have been so successful in selectively breeding cattle to suit these needs, while also exploring the limitations and consequences of this success.

Natural selection describes the process by which organisms best adapted to their environments are the ones that survive and reproduce. The Introductory Activity helps students understand that some traits, such as the ability to digest grass, made certain species more desirable for domestication by humans. The Learning Activities explore how, by nurturing and protecting animals that might not have survived in the wild, human domestication interrupted the process of natural selection. Reproductive success was no longer primarily determined by an animal’s most naturally adaptive survival traits, but rather by its artificially selected traits desirable to humans (primarily milk and meat production). The culminating activity presents a case study in which students consider the consequences of losing the naturally selected attributes of breeds less adapted to domestication.

Students should already be familiar with the concepts of evolutionary adaptation, natural selection, and DNA/genetic engineering.

SUBJECT MATTER: Biology/ Living Environment

LEARNING OBJECTIVES:

Students will be able to:

• Describe the traits of cows that make them suitable for domestication.
• Explain how the cow’s digestive system has adapted to its environment.
• Compare and contrast natural and artificial selection.
• Describe various breeds of selectively bred cattle and their desirable traits.
• Discuss some limitations and negative consequences of selective breeding.

STANDARDS AND CURRICULUM ALIGNMENT:

From the National Science Standards for Science Content, Grades 9-12.

CONTENT STANDARDS C: Life Science
As a result of activities in grades 9-12 students should develop understandings of:

Biological Evolution

• Species evolve over time. Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuing selection by the environment of those offspring better able to survive and leave offspring.
• The great diversity of organisms is the result of more than 3.5 billion years of evolution that has filled every available niche with life forms.
• Natural selection and its evolutionary consequences provide a scientific explanation for the fossil record of ancient life forms, as well as for the striking molecular similarities observed among the diverse species of living organisms.

Behavior of Organisms

• Like other aspects of an organism’s biology, behaviors have evolved through natural selection. Behaviors often have an adaptive logic when viewed in terms of evolutionary principles.

New York State Core Curriculum Alignments
From the Living Environment Core Curriculum.

STANDARD 4: Students will understand and apply scientific principles and theories pertaining to the physical setting and living environment and recognize the historical development of ideas in science.

Key Idea 2: Organisms inherit genetic information in a variety of ways that result in continuity of structure and function between parents and offspring.

Performance Indicator 2.2: Explain how technology of genetic engineering allows for human to alter genetic makeup of organisms.

2.2a: For thousands of years new varieties of cultivated plants and domestic animals have resulted from selective breeding for particular traits.

2.2b: In recent years new varieties of farm plant and animals have been engineered by manipulating their genetic instructions to produce new characteristics.

Key Idea 3: Individuals and species change over time.

Performance Indictor 3.1: Explain the mechanisms and patterns of evolution.

3.1e: Natural selection and its evolutionary consequences provide a scientific explanation for the fossil record of ancient life-forms as well as for the molecular and structural similarities observed among the diverse species of living organisms.

3.1f: Species evolve over time. Evolution is the consequence of the Interaction of (1) the potential for a species to increase its numbers… (4) the ensuring selection by the environment of those better able to survive…

3.1j: Behaviors have evolved through natural selection. The broad patterns of behaviors exhibited by organisms are those that have resulted in greater reproductive success.

3.1k: Evolution does not necessitate a long-term progress in some set direction. Evolutionary changes appear to be like the growth of a bush: Some branches survive from the beginning with little or no change, many die out altogether, and others branch repeatedly, sometimes giving rise to more complex organisms.

MEDIA COMPONENTS

Video

NATURE, Holy Cow, selected segments:

Clip 1, “A Cow’s Digestive System”

Clip 2, “Desirable Breeding Traits in Cattle”

Clip 3, “Different Breeds of Cattle”

Access the streaming and downloadable video segments for this lesson at the Video Segments Page.

Web sites

Breeds of Livestock
An Oklahoma State University Web site featuring photos and descriptions of various breeds of cattle from around the world.

World Climate Map
A map of the world showing different climate zones.

Genetic Engineering
A Regents’ preparatory Web site featuring a description of how the meaty English Shorthorn cow was selectively bred with the heat-resistant Brahman cow to produce the Santa Gertrudis, a hybrid which possesses the positive characteristics of both parent breeds.

Punnett Squares
An interactive Web-site which explains how Punnett squares can be used to determine the likelihood that certain traits will be passed on to future generations.

A Dying Breed
A New York Times article which discusses the pros and cons of increasing hybridization by Bahiman cattle ranchers in Uganda of their native Ankole cattle with Holstein cattle from the United States.

MATERIALS

For each student:

• “Traits of Ankole and Holstein Cattle” Student Organizer (PDF)(RTF)

For each group:

• “Man’s Best Friend?” Student Organizer (PDF)(RTF)
• “Cattle Breeding” Student Organizer (PDF)(RTF)
• “Finding the Balance” Student Organizer (PDF)(RTF)

For the class:

• “Traits of Ankole and Holstein Cattle” Student Organizer Answer Key (PDF)(RTF)
• “Man’s Best Friend?” Student Organizer Answer Key (PDF)(RTF)
• “Cattle Breeding” Student Organizer Answer Key (PDF)(RTF)
• “Finding the Balance” Student Organizer Answer Key (PDF)(RTF)
• Computer with Internet access, projector, and screen

PREP FOR TEACHERS

Prior to teaching this lesson, you will need to:

Preview all of the video clips and Web sites used in the lesson.

Download the video clips used in the lesson to your classroom computer, or prepare to watch them using your classroom’s Internet connection.

Bookmark the Web sites used in the lesson on each computer in your classroom. Using a social bookmarking tool such as del.icio.us or diigo (or an online bookmarking utility such as portaportal) will allow you to organize all the links in a central location.

Next: Proceed to Activities.

Nature vs. Nurture

During the 20th century, as humans have encroached more and more on animals’ territory, zoos have come to be more than just places to view wild animals. They have become breeding facilities, wild animal hospitals, and research centers. As you see in Animal Attractions: Amazing Tales from the San Diego Zoo, a lot goes on behind the scenes, away from the ordinary visitor. And much of this activity is focused on a single goal: trying to save species from extinction.

The thought behind this idea is that as humans have spread across the globe, the breeding, migratory, and behavior patterns of wild animals have been forever changed. Since we cannot put the world back the way it was, scientists reason, we must try to invent new ways to deal with the problem of endangered animals, some of whose ranks have dwindled to the double — or even single — digits.

The Species Survival Plan (SSP) is sponsored by the American Zoo and Aquarium Association (AZA). The plan’s aim is to help “ensure the survival of selected wildlife species” through cooperative captive-breeding and training programs. Zoos share animals with other zoos, which keeps gene pools diverse as well as increasing the chances of conception in the event that a particular male and female don’t seem to have the right “chemistry.”

The Center for Reproduction of Endangered Species at the San Diego Zoo is headquarters for the SSP of the giant panda. If the resident pandas are not on exhibit at the zoo, they are probably under the scrutinizing eye of researchers studying their behavior. This program, headed by scientist Dr. Don Lindburg, began in 1987 as a long-distance collaboration with Chinese scientists at the Woolong Giant Panda Conservation Centre in Sichuan Province, China. This rare species faces the double threat of habitat fragmentation and illegal hunting, even though the latter carries the steep penalty of execution in China. Today, an estimated 1,000 pandas survive in the remote bamboo forest areas of the Qionlai Mountains.

In September, 1996, Lindburg’s team became foster keepers for a 15-year-old rescued male named Shi Shi and a six-year-old captive-born female named Bai Yun, both on loan from Woolong. The pair was introduced in February, 1997, in the hopes that when Bai Yun was ready to mate, Shi Shi would accept her.

They noticed each other, and it was not friendly, but it was not aggressive either,” describes Lindburg of the pandas’ first meeting. “It is sort of what you would expect from a solitary animal.” Wild pandas are rarely found in pairs, unless a mother is nursing a youngster or a couple is about to copulate. To put the pandas “in the mood,” Lindburg rotated them in each other’s play spaces, recording their reactions to various aromas placed in the environment. He eventually put the pair together.

“What happened was that the female became very solicitous,” says Lindburg. “Unfortunately, the male basically ignored her, and then responded to all of her overtures in an unfriendly manner.” Shi Shi growled, chased Bai Yun away, and swatted at her.

This means the researchers will have to wait a whole year to run the process all over again: females receive males only once a year for two or three days, attracting them with a “panda perfume” in the form of scent markings on trees or the ground. Scientists believe that this method is one of the main reasons pandas face extinction: their habitats, once solid swaths of forest, have been split up by a sprawling human population. Now pandas cannot find each other during the crucial one to two days when the female is in season.

Meanwhile, Lindburg and his colleagues are studying Bai Yun and Shi Shi intensely, hoping that their behavior will give researchers a clue as to how to boost the falling population of pandas in the wild.

Update: On Auguest 21, 1999, Shi Shi gave birth to Hua Mei, the first giant panda born in the Western Hemisphere since 1990. On February 11, 2000, visitors to the San Diego Zoo were able to get a glimpse of the baby panda.