Breeds today denote specific variations in size, appearance, behavior and lifespan, yet despite those characteristics, they still share quite a bit with their wolf ancestors. Underneath it all, they are still predators with sharp teeth.

Dogs are different

As noted earlier, dogs and wolves are similar enough to breed together, even today. But what are the differences between them, and how do dogs compare with other members of their species?

Beginning with wolves, if a dog and a wolf are of equal sizes, the dog's skull will be roughly 20 percent smaller; the teeth are proportionately smaller as well. Interestingly, the brain is only 10 percent smaller in the dog, (not 20 percent as you might have guessed).

The way dogs evolved contributed to other differences. They need fewer calories to function than wolves, probably because they learned to survive and thrive on a diet of human scraps and refuse. Over time, that diet also made the heavy jaw muscles of the wolf unnecessary, experts believe. In fact, on theory is that the dog's limp ears (as compared to the upright ears of the wolf) are the result of those jaw muscles atrophying.

Dog paws are a lot smaller than those of a wolf — they are only about half the size, and the dog has sweat glands on their paw pads; wolves don't. The survival advantage of that difference is questionable; some experts attribute it to early cross breeding with coyotes, who have the same sweat glands in their paw pads.

Eyesight

Most mammals are dichromats, meaning they have two-color vision. While that equates to color blindness in humans, it is the normal vision for many animals. Think of a black and white photograph — details and shadings are just as rich and varied, but it's all variations of two colors. People see the whole spectrum because we enjoy trichromatic vision. Dichromats — and there are color blind people who have dichromatic vision — probably don't have the ability to see green to red. If that's true, dogs see mostly in shades of blue and yellow.

Dogs have other visual advantages: like cats, they can see in much dimmer light than we humans. Our species and theirs have retinas composed of rods and cones but the proportion is different: dogs have mostly rods, humans have mostly cones. Rods need less light to function than cones do.

They can also detect motion far better than we can, which makes them very valuable companions for hunting, herding and protection. But overall, we see better than they do. While no one can be completely sure, veterinarians currently believe that if we want to describe the dog's vision in human terms, at our best, we have 20/20 eyesight: dogs have 20/75. Put simply, things we can see clearly at 75 feet away, they can only see at 20 feet away.

As with other mammals, not every dog has perfect vision. Nearsighted, myopic, farsighted — all the vision problems we're familiar with in ourselves also occur in our canine companions. A recent study found that in a group of German Shepherd guide dogs, only 15 percent were myopic, but in another random group of the same breed, 53 percent were myopic. This would seem to indicate that in the guide dogs, genetic selection for normal vision may have occurred. Testing a group of Rottweilers, scientists found that 64 percent were myopic.

Generally, our eyes and the dogs' have similar parts (cornea, retina, etc.). But the dog's retina has a region called the visual streak, which is an oval area centered on the part of the retina closets to the animal’s nose. It is oval in shape, and contains the highest concentration of photoreceptors and ganglion cells (humans have a similar concentrated spot on the retina called the fovea). This area aids the dog's vision in low light, and probably increases their peripheral vision, and their ability to scan the horizon. Sight hounds have a field of vision of up to 270 degrees while the average human can only view 180 degrees.

Hearing

Anyone with a dog knows that their hearing far exceeds ours. Just try to open a package without your dog coming to investigate! Dog whistles, used by hunters and trainers, are undetectable to the human ear but can be heard by dogs over great distances; they are generally in the range of 16 to 22 kHz. Overall, dogs can detect sounds as low as the 16 to 20 Hz frequency range (compared to 20 to 70 Hz for humans) and above 45 kHz (compared to 13 to 20 kHz for humans). That means they can hear sounds at approximately four times the distance we can. They can rotate, cock and adjust their ears; that mobility aids them in determining the exact location of a sound. The amount of ear mobility varies by breed, but overall there are at least 18 muscles that make those motions possible. Floppy eared breeds (think of a Bassett hound) do not hear as well as those with more natural ear shapes.

With some understanding of your dog's hearing abilities, you can more easily train your pet. Dogs distinguish different pitches very clearly, so the tone of your voice is as important as the command itself. All dogs respond quickest to sharp sounds. That's true even for puppies, so when you begin training, add a sharp noise to reinforce your voice command. Handclapping, whistling, using a wooden 'clacker' or castanet will all help the pup react faster to your instruction. Sharpness of tone is important when using the STOP command; otherwise it is just another pleasant word to your pet. Recognize that an unexpected or unusual tone of voice will alert your dog, in the same way that any new noise will. Most will face the direction of the unusual sound to better identify it, and then approach it slowly as they process the data.

Dogs 'feel' sounds through their ears as well. To get a sense of what that is like, sit down in a car with multiple speakers, tweeters and woofers and crank up the volume. You'll feel the vibration of the bass notes throughout your body as well as hear them with your ears. That's how your dog 'feels' sounds too — only for him, many common events produce that sensation, which can be very painful over an extended period of time. Many people report that their dog is 'afraid' of thunderstorms, when in reality the poor animal is significant physical pain from the repeated deep percussive noises of the storm. The same holds true for 4th of July fireworks and other explosives. Since earthquakes produce deep vibrations, dogs are aware of them long before we are. The roar of an airplane reaches your dog's ears before you've seen the plane.

By the same token, dogs hear high pitched noises that are invisible to us. When your animal suddenly starts a frenzied digging out in the yard, moments later revealing a mole or bunny, rest assured he heard the creature beneath the soil and knew just where to find it!

Smell

Some humans have remarkable senses of smell. The perfume industry relies on such individuals for their unique ability to distinguish scents, often from a single whiff. Once upon a time, they were called 'noses' because of their olfactory talents. But most of us humans only have about 5 million smell cells over an area roughly one square inch in size. By comparison, dogs have nearly 220 million smell cells spread over an area about the size of a pocket handkerchief; dogs that have been selectively bred for scent detection have even more than that.

Most agree that dogs cannot be trained to track; those that do so do it naturally. The trainer's job is to keep the dog motivated so it will keep on tracking, and to teach the dog to focus on a single scent. Some scents are carried in the air; others are on the ground; the work is difficult and often tedious. The bond between trainer and tracker is the key to success.

Over the last several years, scientists have begun looking at the dog's olfactory strength as a means to identify illness in people by scent alone. A diagnosis of cancer is often difficult to ascertain in the early, most-treatable stages of the disease when lab work and imaging technologies may be inconclusive as to the presence of cancer cells. However, some dogs can accurately identify the presence of even a few of these deadly cells. In a recent study conducted by the Pine Street Foundation, a cancer research organization in San Anselmo, California, five dogs were trained over a three-week period to identify the smell of lung or breast cancer in the breath of a human patient. After the 21-day training cycle, the dogs were given breath samples of 86 cancer patients and 83 healthy (control) patients in identical containers. The five dogs detected lung and breast cancer with sensitivity and specificity between 88 and 97 percent, even in the early stages of those cancers.

Color

Imagine we are hunting in a forest. The sun filters down on the vegetation and you are looking for a deer. You'll be watching for the sunlight on the top half of a moving animal; when you finally see the deer, there will be a shine along its spine and top fur, while its lower half will be dark, unlit by the sun and in the animal's own shadow. As a predator, you routinely watch for that pattern to find your dinner. No surprise to learn that this has caused prey to evolve away from that easily-discovered coloration. Instead, they developed countershading — dark on top and light on the bottom, confounding the predator's assumptions and blending into the darkness at the lower levels of brush and marsh.

Many dogs are still countershaded — darker on top, with lighter coloring on the lower half, including the common blaze or star of white fur on many canine chests. Overall, today's dogs come in a rainbow of colors, depending on each breed's characteristics. From the familiar black spotted white Dalmatian to the blue American Staffordshire terrier, dogs have departed from their wolf ancestors' colorations thanks to generations of breeding. Put simply, there are two types of pigment creating all dog colors and patterns: eumelanin and phaeomelanin. Each pigment has a default color (eumelanin is black, phaeomelanin is red); those default colors can be changed by a host of different genes.

The black pigment, either straight or modified by another gene, will dictate the color of the dog's eyes and nose as well as its coat. Black, liver, blue or Isabella noses are created by the type of eumelanin a particular dog produces. Iris color is also a result of this pigment; full strength eumelanin produces brown eyed dogs; eumelanin changed or reduced by another gene will give a dog gold or amber colored eyes. The default black of eumelanin can be turned into blue (diluted black) by one set of genes, or turned into isabella (diluted liver) by a different set of genes.

Whatever the coat color of a dog, the nose indicates whether the animal carries the eumelanin pigment.

The red pigment, phaeomelanin, appears as everything from light cream to deep auburn red, including all the various tan colors. This pigment, unlike eumelanin, is only produced in the coat and has no effect on the dog's eye or nose color.

Think of this pigment as one color that extends from deep to light tones. The highest production of phaeomelanin occurs in the Irish Setter and others with deep red coats. Golden Retrievers and other breeds with less phaeomelanin are golden or tan, the lighter versions of the red pigment. While it is known that the default color of eumelanin is black, at this time it is simply presumed that the default color of phaeomelanin is golden. As genetic research continues, this will no doubt be confirmed or disproven within the next several years.

White dogs lack both of these pigments. Look closely at the coat of a white dog; you’ll often find they possess an ivory or cream highlight, which is the indication that they do produce slight amounts of phaeomelanin; eumelanin is unaffected by this quality, which is why white dogs (except for albinos) will still have black/liver/blue or Isabella noses and brown eyes. If they lack enough eumelanin, they will have a pink nose and blue eyes. Albinos fully lack pigment; a true Albino would have red eyes. There are no full (true) Albino dogs; there are degrees of Albino that present in certain breeds, and there are dogs with such diluted pigment that they appear to be without any at all. Most are pale eyed, not red-eyed. Chinchilla and platinum whites are created by a gene that dilutes phaeomelanin to such a degree that it becomes white.

Heads you lose, tails you win

The wolf's tail is long, densely furred and has a rounded end. It accounts for roughly one quarter of its body length. Although they are usually seen with their tails down, wolves are capable of holding them up if they wish. While some dogs have similar tails (the Alaskan Husky and the Lapponian Herder, for example), there are as many other shapes as there are breeds of dog. Long and short, straight and curly, down or up, cork-screwed or coiled — all that and everything in between as well. Naturally occurring bob tails occur in over a dozen different breeds as a genetic trait.

In some breeds, the tail is traditionally docked to avoid injuries (especially for hunting dogs). Animal rights activists, pet owners and veterinarians have recently challenged this practice on a number of grounds; it will be interesting to see if the larger kennel clubs change their breed standards accordingly. In the E.U., the European Convention for the Protection of Pet Animals bans ear cropping and tail docking. This doctrine became effective in 1992, although several nations specifically did not sign it initially so as to continue docking tails in their countries (the U.K. and France both opted for that approach; both nations later banned the practice). Today, only a handful of nations allow dogs' tails to be docked.

Sprint metabolism

Dog owners often remark that one minute, their animal is racing around the house; the next moment, they plunk down without warning for an immediate rest. That, in a nutshell, is their sprint metabolism at work. For a short period of time, your dog is capable of creating a great deal of energy. The actual capacity of their heart and lungs (both of which are oversized) is well beyond its everyday needs. Additionally, dogs have more red blood cells than a human does, relatively speaking. Until those are needed, they are stored in the spleen. When the dog suddenly needs (or wants) to use its full metabolism (fighting off another animal will create the need; so will your offer to play catch with his Frisbee), the extra cells are released into the bloodstream and suddenly, the dog's entire system ramps up to full capacity. That frenzy of activity will produce copious quantities of internal heat. Covered in fur, with limited sweat glands, cooling down is difficult for dogs. They can only lie down, pant and wait to cool off. So after a short time, the dog has to stop all that accelerated activity or risk harm from overheating. Next time your dog suddenly stops a vigorous game of fetch to go lie down and pant in the shade, you'll know its his sprint metabolism at work.