Dog

The dog (Canis familiaris) is the domesticated companion we know as man's best friend. Dogs vary enormously in shape, size and colour. A Great Dane can weigh 50-79 kg and stand 71-81 cm tall, while a Chihuahua may weigh just 0.5-3 kg and stand 13-20 cm.

Dogs have powerful jaws with about 42 teeth, and a skeleton well suited to running. Their coats are either double, with a coarse guard hair over soft down, or single, with a topcoat only. Some breeds are hairless and others have thick corded coats.

People keep dogs for companionship, and also for hunting, herding, pulling loads, protection, therapeutic support, assisting people with disabilities, and police and military work. There are around 450 official breeds, more than any other mammal.

Dogs are descended from wolves. They share a common ancestor with the modern grey wolf, and DNA shows all dogs descend from an ancient, extinct wolf population distinct from any modern wolf lineage. The dog was the first species to be domesticated, before farming began, by hunter-gatherers.

The earliest remains generally accepted as a domesticated dog, found at Bonn-Oberkassel in Germany, date to about 14,223 years ago. That dog was buried alongside a man and a woman. It had survived canine distemper as a puppy, which would have been unlikely without human care. Genetic studies suggest domestication may have started over 25,000 years ago, though exactly when and where is still uncertain.

Most modern breeds come from small numbers of founders within the last 200 years. Dogs began diversifying in the Victorian era, when people took control of breeding. The keeping of dogs as companions, particularly by elites, has a long history, and from the second half of the 20th century more owners came to see their dog as part of the family.

Dogs have been shaped by thousands of years of contact with people. They can understand and communicate with humans, and are unusually attuned to human behaviour. Compared with wolves, dogs tend to be less timid and less aggressive, and they were bred mainly for desirable behaviour.

Dogs communicate through eye gaze, facial expression, barking and other sounds, body posture, and scent. Tail movements show emotional state. They mark territory by urinating, which is more likely in a new environment. Puppies begin socialising with other dogs at around 3 to 8 weeks, and at about 5 to 12 weeks their focus shifts from dogs towards humans.

Their senses are sharp in some ways. Dogs have roughly forty times more smell receptors than humans and hearing up to four times better. Their vision is dichromatic, mostly yellows, blues and greys, and less acute than ours. Border Collies have been recorded learning the names of hundreds, and in one case over 1,000, words.

Some dogs have a strong prey drive, which breeding can influence. Dogs can become aggressive from fear, anxiety, trauma or abuse, territorial protection, or guarding something they value.

Many disorders are known to affect dogs, some present from birth and others acquired. These include heart, kidney, liver, skin, eye, joint, hormonal and digestive conditions. Cancer is the most common cause of death, and heart and kidney failure are other common causes.

Common parasites include fleas, ticks, lice, mites and worms. Common infections include canine distemper, parvovirus, adenovirus, leptospirosis, canine influenza and canine coronavirus, and vaccines exist for all of these.

Dogs are the companion animal most often reported for exposure to toxins. Chocolate, xylitol, grapes and raisins, garlic and onions, human drugs and cleaning products are among the commonly reported culprits, and metaldehyde, a common slug and snail pesticide, typically causes severe outcomes when eaten.

Median lifespan is about 12.7 years, though it varies widely between breeds. Obesity is linked to shorter lives, and one study found obese dogs had a life expectancy about a year and a half less than dogs of healthy weight. A 2024 UK study of 584,734 dogs found purebreds living longer than crossbreds, although other studies suggest mongrels live about a year longer than pedigrees. Small dogs with longer muzzles tend to live longer than medium-sized dogs with much flatter faces.

This is general awareness only, not veterinary advice. Always consult a vet about your pet's health.

How long do dogs live?

The median lifespan is about 12.7 years, though it varies widely between breeds. Weight, size and muzzle shape all appear to make a difference.

Can dogs see colours?

Yes, but fewer than we do. Dogs see mainly yellows, blues and greys, and have difficulty telling red from green.

Can dogs give people diseases?

Dogs can be a source of zoonoses, including leptospirosis, ringworm, toxocariasis, hydatid disease and pasteurellosis. Worldwide dogs cause 99% of rabies cases, but in the UK rabies is absent from dogs and is only carried by bats.

How much do dogs vary in size?

A great deal. A Chihuahua can weigh as little as 0.5 kg, while a Great Dane can reach 79 kg. All healthy dogs have the same number of bones, apart from the tail.

Is the alpha dog idea true?

Not really. The idea of an alpha dog trying to dominate is based on a controversial theory about wolf packs, and it has been disputed that trying to achieve status characterises dog-human interactions.

Can all dogs swim?

Not all. In one study of 412 dogs, around 36.5% could not swim, while the rest swam in a pool unaided.

Dogs may be able to sense small variations in Earth's magnetic field, and one study found they prefer to defecate with their spines aligned north-south in calm magnetic conditions.

Because of their long history with people, dogs can thrive on a starch-rich diet that would be inadequate for other canids.

Dogs have an upturning tail, which Linnaeus cited in 1758 as a reason to treat them as separate from wolves.

The skull, body and limb proportions across dog breeds show more variety than is found in the whole order of carnivores.

In 1957 a dog named Laika became one of the first animals launched into Earth orbit.

Dogs seem to respond more positively to social rewards than to food rewards, according to one brain study.