Dog

The dog (Canis familiaris or Canis lupus familiaris) is a domesticated relative of wolves. It is also called the domestic dog. Hunter-gatherers selectively bred dogs during the Late Pleistocene. Dogs and the modern gray wolf share a common ancestor. Dogs were the first species to be tamed, more than 14,000 years ago, before farming began. Some scientists think the process may have started even earlier, over 25,000 years ago. Because dogs have lived with humans for so long, they can eat a starch-rich diet that other canids could not easily digest.

People have bred dogs for certain behaviors, senses, and body features. Dog breeds come in many shapes, sizes, and colors. Dogs have the same number of bones as humans, except for the tail. They have strong jaws and many teeth. They also have good senses of smell, hearing, and sight. Compared to humans, dogs smell and hear much better, but their visual acuity is weaker. Dogs do many jobs for people. They help with hunting, herding, pulling loads, protection, companionship, and therapy. They also help disabled people and assist police and the military.

Dogs communicate in many ways. They use eye contact, facial expressions, sounds, body posture, and movements of their bodies and legs. They also use smells, pheromones, and taste. Dogs mark their territory by urinating on it, which they do more often in a new place. Over thousands of years, dogs have adapted well to life with people. They can understand and communicate with humans. Communication in dogs and the human–canine bond have been studied often. Dogs have had a big influence on human society, so they have earned the nickname "man's best friend" (sobriquet).

Scientists estimate there are between 700 million and 1 billion dogs in the world. Dogs are distributed around the world. The dog is the most popular pet in the United States, where it lives in about 34 to 40 percent of homes. Developed countries have about 20 percent of the world's dogs. Most dogs, around 75 percent, live in developing countries. Many of these are feral or street dogs.

Taxonomy

Further information: Canis lupus dingo § Taxonomic debate – the domestic dog, dingo, and New Guinea singing dog

Dogs are domesticated members of the family Canidae. They belong to the Canis genus, along with wolves (Canis lupus). Some people have considered dogs a subspecies of Canis lupus. The dingo is usually considered a type of dog. Studies of genes show that dogs likely split from wolves between 27,000 and 40,000 years ago. Hunter-gatherers tamed wolves into dogs at least 14,000 years ago, before farming began. The dingo and the New Guinea singing dog developed after geographic isolation and after some dogs went wild in Oceania, over 8,000 years ago.

In 1758, the Swedish scientist Carl Linnaeus gave the domestic dog the name Canis familiaris. He thought it was a separate species from the wolf because of its upturned tail. Scientists have grouped dogs and wolves in different ways over time. In Australia, how dingoes are classified is also a political question, because it affects how dingo populations are managed. The oldest remains clearly identified as a pet dog were found in Bonn-Oberkassel, Germany, and are about 14,000 years old. Today there are around 450 official dog breeds, more than any other mammal. Most breeds were formed in the last 200 years, starting in the Victorian era, when people began controlling how dogs were bred.

Domestication

Main article: Domestication of the dog

Breeds

Anatomy and physiology

Dogs vary greatly in size. The Great Dane is one of the largest breeds, weighing 50–79 kg (110–174 lb). The Chihuahua is one of the smallest, weighing 0.5–3 kg (1.1–6.6 lb). All healthy dogs have the same number of bones, except in the tail, though skeletons differ between types. The skeleton is well suited for running. The vertebrae in the neck and back have extensions for epaxial muscles and hypaxial muscles. The long ribs leave room for the heart and lungs. The shoulders are not attached to the skeleton, which allows flexibility. Since dogs were first tamed, breeding has made some dogs larger, such as mastiffs, and others smaller, such as terriers. Dwarfism has been bred into some types with short legs, such as dachshunds and corgis. Most dogs have 26 vertebrae in their tails, but some with naturally short tails have as few as three.

The skull has the same parts in every breed, but its shape differs a lot. Some types, like sighthounds, have long skulls. Others have very short, broad ones. Dogs have about 42 teeth. Their carnassial teeth cut food into bite-sized pieces. Dogs have senses of sight, hearing, smell, taste, and touch. They also have magnetoreception. One study suggests they can feel small changes in Earth's magnetic field. Their sense of smell is the strongest sense they have. They have many more smell-sensitive receptors than humans do, and they can hear sounds from much farther away. Dogs also have whiskers that sense air changes and nearby objects. A dog's dewclaw is the fifth digit on its legs. Dog coats come in "double" or "single" types. The Yorkshire Terrier is often groomed into a set style. The tail is the end of the vertebral column. It helps a dog show its feelings and keep its balance. Some dogs have a violet gland on the tail. The tail can be hurt by forceful wagging, which is called kennel tail. Some hunting dogs have had their tails docked to prevent injuries. However, many American Veterinary Medical Association and British Veterinary Association groups oppose this practice.

Health

Many congenital and acquired disorders can affect dogs. Dogs can have problems in the nasal cavity, larynx, and trachea, and in the lungs, such as pulmonary disease. They can also have heart diseases, blood problems like anaemia and clotting disorders, and stomach problems like diarrhoea and gastric dilatation volvulus. Other problems include hepatic diseases such as liver failure, pancreatitis, renal disease, bladder problems like cystitis, and hormone problems like diabetes mellitus and hypothyroidism. Dogs can also have seizures, arthritis, skin conditions like alopecia, eye diseases like glaucoma, and neoplasia. Common dog lice, fleas, ticks, and mites can bother dogs. Rabies is a serious disease that dogs can pass on to people. There are vaccines for many common infections, such as canine parvovirus and canine distemper virus. Dogs often come into contact with toxins, and most of these poisonings are accidents. The most common food poisoning is theobromine poisoning from chocolate. Neoplasia is the most common cause of death for dogs, followed by heart and renal failure.

Lifespan

Further information: Aging in dogs

The lifespan of dogs depends a lot on the breed. The typical (median) lifespan is about 12.7 years. Overweight dogs tend to live about a year and a half less than dogs at a healthy weight. A 2024 study in the UK found that purebred dogs lived longer than crossbred dogs. The authors noted that designer dogs were counted as crossbred, and that purebred dogs often received better care. Other studies show that fully mongrel dogs live about a year longer on average than dogs with pedigrees.

Reproduction

Main article: Canine reproduction

Dogs usually reach sexual maturity around six months to one year old, though some large breeds take up to two years. Female dogs have an estrous cycle that usually lasts 4 to 20 days. A litter usually arrives about 63 days after fertilization. An average litter has about six puppies. Neutering means removing the reproductive organs through gonadectomy. In male dogs this is orchidectomy, and in female dogs it is ovariohysterectomy. Neutering can reduce some problems, and spayed females are less likely to develop some cancers. However, it can also raise the risk of other health problems, such as urinary incontinence, prostate cancer, and obesity. The ASPCA advises neutering dogs not meant for breeding. The Society for Theriogenology and the American College of Theriogenologists oppose required neutering.

See also: Inbreeding depression

Mating close relatives, which is common for pet dogs, has been linked to smaller litters and lower survival. One study of Dachshund litters found that more puppies were born dead as inbreeding increased. A study of Boxer litters found that many puppies died before 7 weeks of age.

See also: Dog intelligence

See also: Dog behavior § Behavior compared with other canids

Dogs have been shaped by thousands of years of living with people. This helps them understand and communicate with humans, and they pay close attention to human behavior. Scientists say that domestic dogs have social thinking skills that their wild relatives and very smart animals such as great apes do not have. These skills are similar to those of children. Dogs have about twice as many neurons in their cerebral cortex as cats, which suggests they could be about twice as smart. Most farm animals were bred for useful goods, but dogs were bred for behavior traits people liked. A 2016 study found that only 11 fixed genes differed between wolves and dogs. This showed artificial selection and changes in behavior and body features. Most of these genes affect the catecholamine synthesis pathway, the fight-or-flight response, and emotional processing, which is linked to tameness. Compared with wolves, dogs tend to be less shy and less aggressive, though some of these genes are linked to aggression in certain breeds. High sociability and lack of fear may involve genetic changes related to Williams-Beuren syndrome in humans. These changes can make people very social, but they may reduce problem-solving ability. A 2023 study of 58 dogs found that some dogs similar to those with attention deficit hyperactivity disorder had lower levels of serotonin and dopamine. Dogs can become aggressive after being hurt or treated badly, from fear or worry, when protecting their territory, or when guarding things they value. Acute stress reactions from post-traumatic stress disorder (PTSD) can grow into chronic stress. Police dogs with PTSD can often refuse to work.

Researchers have tested how dogs take in information, remember it, and use it to solve problems. A study of Rico, a Border Collie, showed that he knew over 200 item names and learned new names through inference. Another Border Collie, Chaser, could link over 1,000 words to items. Dogs' thinking abilities are similar to those of horses, chimpanzees, or cats. Dogs show a theory of mind by engaging in deception. Australian dingos did better than domestic dogs at solving problems that did not involve people.

Dogs have an instinct called prey drive. This term is mostly used to describe training dogs' habits, and breeding can influence it. It can make dogs see objects or animals as prey or act possessively. It has been strengthened in some breeds so they can hunt vermin or other pests. Puppies or dogs sometimes bury food underground. One study found that wolves were better at finding food caches, likely because of a "difference in motivation." Some puppies and dogs engage in coprophagy out of habit, stress, a wish for attention, or boredom, and most stop later in life. A study suggests this behavior was inherited from wolves, where it likely reduced intestinal parasites in dens. Most dogs can swim, though in a study of 412 dogs, about 36.5% could not. The rest could swim without a trainer in a swimming pool. A study of 55 dogs found a link between swimming and improvement in the hip osteoarthritis joint.

Dogs mark their territories by urinating on them. They use eye gaze, facial expressions, sounds, body posture, and scents to communicate. People talk to dogs using voice, hand signals, and body posture. Dogs use their good hearing to understand barking patterns. A study using functional magnetic resonance imaging (fMRI) found that dogs respond to voices in a brain region near the temporal pole, similar to humans. Dogs also tend to respond more positively to social rewards than to food rewards. A female dog (bitch) may produce colostrum, a nutrient-rich milk, 1–7 days before giving birth. Milk production lasts about three months.

Ecology

Dogs are the most common large carnivoran living near people. In 2020, there were an estimated 700 million to 1 billion dogs in the world. A study found that the dog is the most popular pet in the United States, living in about 34 out of every 100 homes. About 20% of dogs live in developed countries. In 2011, World Animal Protection estimated that about three-quarters of the world's dogs live as feral, village, or community dogs. Most of these dogs are scavengers that have never been owned by people. Feral and free-ranging dogs have a hard time competing with other large carnivores because they live so closely with humans. Wolves sometimes kill dogs, but wolves often live in pairs and are heavily hunted, so they are at a disadvantage against large groups of dogs. Coyotes and big cats have also attacked dogs. Leopards prefer dogs and have been recorded hunting them, whatever their size. Siberian tigers in the Amur river region have taken dogs in the middle of villages, and striped hyenas are known to hunt dogs in their range. Dogs have also affected wildlife. They have helped make 11 vertebrate species extinct, are a 'potential threat' to at least 188 threatened species around the world, and have been linked to the extinction of 156 animal species. In New Zealand, which had no native land-based mammals before people arrived, dogs have changed the ecology. Dogs have also killed a few birds of the endangered kagu in New Caledonia.

See also: Dog food

Dogs are usually described as omnivores. Dogs from farming societies have extra copies of amylase and other genes that help them digest starch, so they can do well on a diet rich in starch. Some dog breeds produce amylase in their saliva, similar to humans. Dogs can only combine bile acid with taurine, and they must get vitamin D from their food. Dogs cannot make ten of the twenty-one amino acids common to all life forms, including selenocysteine: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Like cats, dogs need arginine to keep their nitrogen balance, which places dogs halfway between carnivores and omnivores. Some places never had dogs. These include the land of the Aboriginal Tasmanians, who were cut off from Australia before dingos arrived there. They also include the islands of the Andamanese peoples, who were cut off when rising sea levels covered the land bridge to Myanmar. The Fuegians instead tamed the Fuegian dog, a type of canid that is already extinct. Several Pacific islands never had dogs, or lost them soon after people first settled there. These islands include the Mariana Islands, Palau, most of the Caroline Islands (with exceptions such as Fais Island and Nukuoro), the Marshall Islands, the Gilbert Islands, New Caledonia, Vanuatu, Tonga, the Marquesas, Mangaia in the Cook Islands, Rapa Iti in French Polynesia, Easter Island, the Chatham Islands, and Pitcairn Island. On Pitcairn Island, the Bounty mutineers got rid of their dogs so that passing ships would not find them. Dogs were brought to Antarctica as sled dogs. Starting in December 1993, dogs were banned there by the Protocol on Environmental Protection to the Antarctic Treaty international agreement because of the possible risk of spreading infections.

Roles with humans

Main article: Human–canine bond

See also: Dog show

The domesticated dog first lived as a predator and scavenger. It inherited some behaviors from its wolf ancestors, such as bite inhibition. This may help explain why dogs are easy to train, playful, and good at living with people. Dogs do many jobs for people. They can go hunting, herd animals, pull loads, offer protection, help police and the military, keep people company, and help people with disabilities. In the Western world, people often call dogs "man's best friend." In some cultures, however, dogs are also a source of meat.

Dogs have long been kept as pets. The number of pet dogs grew after World War II, when more families moved to suburbs. Many owners now see their dog as part of the family. Some families enjoy activities together, such as dog dancing and dog yoga. Dogs also help as herding animals, search and rescue dogs, detection dogs, and police dogs. Some dogs take part in shows and dog sports. Dog meat is a social taboo in most parts of the world, although it is still eaten in some East Asian countries.

Terminology

• Dog: the species (or subspecies) as a whole. It also means any male dog.
• Bitch: any female dog.
• Puppy or pup: a young dog under 12 months old.
• Sire: the male parent of a litter.
• Dam: the female parent of a litter.
• Litter: all the puppies born at one time from the same mother.
• Whelping: when a female dog gives birth.
• Whelps: puppies that still depend on their dam.