NATURE’s two-part special Dogs That Changed the World tells the epic story of the wolf’s evolution, how “man’s best friend” changed human society and how we in turn have radically transformed dogs.

From the tiniest Chihuahua to the powerful and massive English Mastiff, modern domesticated dogs come in a bewildering array of shapes and sizes, with an equally diverse range of temperaments and behaviors. And yet, according to genetics, all dogs evolved from the savage and wild wolf — in a transformation that occurred just 15,000 years ago.

In Part One, “The Rise of the Dog,” you’ll learn about how the domestication of dogs might have taken place, including the theory of biologist Raymond Coppinger that it was the animals themselves — and human trash — that inspired the transformation. The genetic analysis of Peter Savolainen of the Royal Institute of Technology in Sweden has placed the origins of domesticated dogs — and those of the first dog — in East Asia. You’ll also discover 14 dog breeds that controversial genetic studies show are the most ancient — and the best living representatives of the ancestors to all living dogs.

Preview Part Two: Dogs by Design

Over 400 breeds of dog are recognized around the world, each unique for its personality, habits, and form. Most of these breeds exploded onto the scene over the past 150 years, spurred by the Victorian-era passion for the “dog fancy” — the selective breeding of dogs to enhance particular characteristics. By tinkering with its genetics, humans made the dog the most varied animal species on the planet — and also created a host of hereditary health problems.

Despite the plethora of new shapes and sizes, dogs have retained the instincts bred into their ancestors by thousands of years of work: the urge to herd or hunt, to dig and to guard. In Part Two, “Dogs by Design,” you’ll discover how these hard-wired behaviors help different types of dogs, from hounds to herders, excel at different tasks (and why it can sometimes be so difficult to train them to do otherwise). You’ll also learn how dogs’ finely tuned senses are serving humans and saving lives. Buy the DVD. This film premiered April 2007.

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.

Why do puppies make such wonderful pets? “If you have to ask, you’ve never owned a dog,” laughs Ellen Hovde of Middlemarch Films, one of the two producer-directors of NATURE’s Dogs: The Early Years. “It’s a matter of unquestioning love: you don’t get it from people, but you get it from dogs.”

Dogs and humans are ideal partners. That’s partly because the dog is a social animal that thrives in the company of his family, whether canine or human. Dogs are by nature loving, loyal, protective, and, in many cases, model employees: “Dogs began as wolves and were bred by human beings for very specific jobs,” Hovde explains. “You have dogs that were bred as workers, like service and seeing-eye dogs, hunting dogs, dogs that were bred as companions. For hundreds of years, we’ve been refining them.” The end result of this careful breeding: a species designed to be our ideal partners in work and play.

Dogs and humans are ideal partners

Has reading all this made you want a puppy of your own? Before you make your decision, think carefully. Puppies — who grow up to be bigger, somewhat less cute dogs — require lots of attention and more than a little cash. Imagine training a squirmy, energetic puppy to come, sit, and stay. Remember that for the rest of her life, you’ll be walking your pooch several times a day and paying for food, medical care, and supplies. Are you ready for the time commitment and financial responsibility? Will you still be in love with your adorable little puppy when she grows up to be a large, messy dog that may outweigh you? If the answer is still yes, here are some tips on achieving puppy love.

Mutts vs. Purebreds:

There are two basic varieties of puppies: purebreds and mixed breeds, sometimes called mutts or mongrels. If you adopt from a shelter, you’ll probably be taking home a mixed-breed dog. Owning a mutt comes with some advantages. For one thing, getting one can be much less expensive than purchasing a purebred from a breeder, which can cost hundreds of dollars. Then too, mutts are free of some of the genetic health problems from which purebred dogs can suffer. It’s also a wonderful feeling to know you’ve saved a dog’s life! Petfinder can help you locate a shelter in your area.

If you’re looking for a purebred, examine your motives: Are you trying to replace a dog you loved as a child? Do you admire a friend’s pedigreed pup? Have you always liked the looks of a particular breed? Think about it carefully. What makes a “good dog” is temperament and training, not looks. The most important thing about the puppy you take home is that you get along well.

Buyer Beware

If you have your heart set on taking home a specific breed, a breeder is the way to go. Inbreeding — the breeding of animals related to one another — can result in inborn illnesses in purebred dogs. Experts caution that many of the dogs for sale at pet stores come from “puppy mills” where inbreeding has led to health problems. So it’s important to get your purebred dog from a responsible breeder; even though it’s more expensive, your dog is much more likely to be healthy. To find a breeder near you, check out the American Kennel Club’s Breeder Referral Search.

Here are some people-friendly dog breeds:
Golden retriever: A warm, gentle, laid-back breed.
Shetland sheepdog: Very energetic and fun-loving, eager to please.
Labrador retriever: The ideal family dog, sweet-natured and loyal.
German shepherd: Intelligent, agreeable, obedient — a good all-around dog.
Maltese: Excellent with children, needs less exercise than larger breeds.
Poodle: Responsive, easy to train, and extraordinarily bonded to its humans.

No matter what kind of puppy you decide to take home, don’t make your decision based on looks alone. Spend as much time with the dog as you can and try to gauge her temperament: Is she shy? Friendly? Aggressive? See how she reacts to strangers and surprises like loud noises. Some early detective work can help you find just the right puppy for you.

Puppy Health

Once you get your puppy home, make sure that your new friend is in the best of health, physically and mentally. Here are some things you should expect to take care of:
Spaying/neutering: Fixing your puppy helps cut down on pet overpopulation.
Vet visits: Schedule an annual trip to the veterinarian for a routine examination that includes shots, and flea and tick prevention. A sick or injured dog may require more care, meaning higher bills.
Training: For your and his own safety, it’s essential to train your puppy to heed your commands, from “sit” to “stay,” “come” to “heel,” and many more. If you’re having trouble training him yourself, a local obedience school can work wonders.
Dog license: Your town may require that you license your dog and get a set of tags to show that she’s had her shots.

Essential Puppy Supplies

Keep your dog happy, healthy, and safe by having these on hand:Leash: Keep your puppy from running off when you go out. Leather leashes cost more than cotton or nylon ones, but can be more comfortable for you to hold.
Collar: Think loose: you should be able to get two fingers between the collar and your dog’s neck.
I.D. tag: Put your phone number on your puppy’s tag in case she ever wanders off.
Dog brush: Brushing your puppy often will keep her coat healthy and shiny.
Shampoo: Experts recommend bathing your puppy about once a week.
Nail clippers: Clip your puppy’s nails regularly to keep them from cracking and splintering.
Food bowl: If your puppy is a larger variety, she may be more comfortable eating out of a raised dish.
Water dish: Every day, dogs need to consume about two and a half times as much water as food, so make sure to refill the bowl often with clean water.
Toys: If you don’t get him a toy to sink his teeth into, your puppy may give your shoe a chew instead

Choosing a puppy isn’t child’s play, as NATURE illustrates in Dogs: The Early Years.
Puppies of any breed enchant and beguile us. But choosing one as a pet solely on the basis of its visual appeal can lead to a mismatch with unfortunate consequences for both owner and dog. Dogs: The Early Years presents an incisive look at the breeding, behavior, and training of humankind’s best friend, including useful pointers on how to avoid mistakes when selecting a puppy.

To choose a compatible puppy for a relationship that will last the dog’s lifetime, it’s important to understand the history of the breeds the prospective owner is considering. Viewers are shown, for example, that dogs bred for the outdoor work of hunting, tracking, herding, or retrieving are not wise choices for people seeking a quiet companion or a gentle playmate for their children. Besides helping viewers make informed choices about puppies, the program illustrates the importance of proper training — also key to a satisfying relationship.

To order a copy of Dogs: The Early Years, please visit the NATURE Shop.

Online content for Dogs: The Early Years was originally posted September 2004.