Dogs came from wolves, a very long time ago, and they have lived with people for at least 14,000 years. They belong to a family of animals called canids, along with wolves, coyotes, foxes and jackals; people still argue about when, where and how dogs were domesticated, and scientists have worked out the time, place and ancestry of nearly every other domesticated animal, from sheep to chickens, but not dogs. Some archaeologists say there were domestic dogs by at least 15,000 years ago; how much earlier is argued, with some saying 30,000 years. Most genetic evidence says dogs emerged in the farming era, but some dog fossils are much older, dating as far back as about 33,000 years ago. One article says dogs worked for people as shepherds, guard dogs and hunters from the beginning of their domestication, and calls the pet-and-family bond a relatively recent thing.
Dmitri Belyaev asked Lyudmila Trut to lead an experiment with foxes, which are closely related to dogs, to see how domestication unfolded and which evolutionary forces were at work. Scientists chose Siberian silver foxes for it because they are close genetic cousins of wolves. Trut worked on the fox experiment from 1959, and continued it after Belyaev died in 1985; it began hidden inside a larger program to breed better foxes for the fur industry. Trut tested each fox by seeing how it reacted when she approached its cage, opened the door and put in her gloved hand, and the calmest foxes were bred to make the next generation. As the experimenters kept choosing the calmest foxes, later generations were calmer and new behaviors began to appear; after about 15 generations of selective breeding, the experiment had foxes that could live with people.
In 2015 a study found that when a dog gazes at its owner, the owner's oxytocin level rises, which prompts more social contact. In the study, 30 dog owners spent half an hour with their dogs, and owners whose dogs gazed at them longest had the biggest rises in oxytocin. Owners who got more gazes looked back, touched and talked to their dogs more, and dogs that got the most attention in return also had the biggest oxytocin spikes, so each raised the other's oxytocin in a loop. Eleven pure-bred wolves raised by people did not make regular eye contact with their owners, and their gaze did not raise the owners' oxytocin. Some scientists say it is too early to tell whether the gaze loop evolved with domestication, because the same loop might also form between puppies and any caregiver, including a dog mother.
A Duke study of 44 dog puppies and 37 wolf puppies, 5 to 18 weeks old, tested how well puppies read human gestures. The dog puppies followed a person's pointing at hidden food without training, but the wolf puppies did no better than chance. The wolf puppies had near-constant human contact from just after birth, and were hand-fed, so the difference was not due to a lack of time with people. Chaser the border collie was trained by retired psychology professor John Pilley starting in 2004, and he showed her 1,022 objects in total. Chaser was tested for three years, and in 838 tests she never scored below 90 percent, according to the researchers' report. Before Chaser, Rico, a border collie in Germany, held the record by being taught about 200 objects, which inspired Pilley to train Chaser. Chaser also understood that objects belong to groups such as balls and Frisbees.
About 12 percent of the air a dog breathes in detours into a recessed area at the back of the nose that is only for smelling, and the rest goes to the lungs. In that smelling area, odor-laden air passes through scroll-like bony structures called turbinates, and receptors in the tissue that lines them recognize odor molecules by their shape and send signals to the brain. When a dog breathes out, the air leaves through slits at the sides of its nose, which helps bring in new smells and lets dogs sniff almost continuously. A dog's nostrils each reach only a small area, which helps it tell which nostril a smell came in through and so work out where the smell is coming from. In a study in Norway, a hunting dog with its head high into the wind sniffed in a continuous stream of air for up to 40 seconds, across at least 30 breaths.
Dogs also have a vomeronasal organ, also called Jacobson's organ, a second smell system we do not have, built for chemical communication. The organ's pheromone signals go to their own part of the brain, so they do not get mixed up with ordinary smells. In one study, dogs led at right angles to a trail that a person had just walked could tell which direction the person went from as few as five steps. A dog researcher wrote that a dog could detect a teaspoon of sugar in a million gallons of water, about two Olympic-sized pools. A dog's nose has more than 100 million smell receptors, while a person's has about 6 million; the part of a dog's brain that works on smells is about 40 times bigger than the same part of a person's brain. A wet nose helps a dog smell because scent particles stick better to damp surfaces.
Working dogs often use their excellent sense of smell to help where people fall short; service dogs are individually trained to perform specific tasks for people with disabilities under the Americans with Disabilities Act. Morris Frank read about dogs trained to guide blinded veterans of World War I in 1927, and he founded America's first guide-dog school with Dorothy Eustis in 1929. As of November 2026, the oldest existing guide dog school in the world is the Seeing Eye in New Jersey. The Seeing Eye works with three main breeds, German shepherds, Labrador retrievers and golden retrievers, and up to 230 people who are blind are partnered with one of its dogs each year. Sled dogs have worked too: in 1925 sled dog teams carried medicine across Alaska to the town of Nome, and more than 20 mushers and their dog teams passed the medicine along in the 1925 relay. Every March, sled dog teams race in the Iditarod, which remembers the 1925 serum run.
Search and rescue dogs use their noses to find missing people, including after disasters; training a reliable search-and-rescue dog often takes several years. In FEMA training, dogs search plastic bark barrels with an opening just big enough for a snout, and only one has a person inside. Dogs trained to find living people usually work as tracking, trailing or air-scent dogs; tracking and trailing dogs follow the scent of one specific person. Herding dogs move sheep by pressure: the dog must learn how and when to press on the sheep to keep them moving the right way. Breeders have sharpened the border collie into a dog whose predator-like behavior makes sheep wary but does not end in a kill. In a stockdog trial, a handler directs a border collie with whistles to gather sheep, drive them through gates and put them in a pen.
Brachycephalic dogs are flat-faced breeds with shorter skulls, like pugs and bulldogs; people bred them to have these features and found the look attractive. BOAS, short for brachycephalic obstructive airway syndrome, is a chronic disease of short-skulled dogs in which narrowed airways cause noisy breathing and can limit exercise, sleep and coping with heat. From 2021 to 2024 a team in England studied nearly 900 dogs of 14 short-skulled breeds, and found 12 of the 14 breeds had some breathing abnormality. In the study, 89 percent of Pekingese and 82 percent of Japanese Chin were affected by BOAS, rates like those of pugs, French bulldogs and bulldogs. From 2006 to 2016 the number of registered bulldogs in the U.S. went up by 60 percent and French bulldogs by 476 percent. The most severely affected flat-faced dogs struggle constantly to get air, but many owners think this is normal for the breed and do not seek treatment. A veterinary professor argues that breeders and vets should be trained to grade the fitness of dogs before breeding to avoid producing offspring with the worst problems.
A wagging tail or a crouching body does not always mean a dog is friendly; one study showed dogs videos of other dogs wagging their tails: dogs that watched a dog wag to the left had faster heart rates and looked anxious, but those that watched a dog wag to the right stayed relaxed. The same research team had found that dogs wag to the right when they feel positive emotions and to the left when they feel negative ones; the researchers do not think the dogs are necessarily meaning to tell other dogs. Before you pet a dog, ask its owner if it is okay. If a grown-up says you can, let the dog sniff your closed hand first; leave a dog alone when it is eating, sleeping or chewing on a toy. If a dog you do not know comes up to you, stay still and quiet instead of running.
A new analysis of the bones and teeth in a grave at Bonn-Oberkassel found two dogs, an older dog and a younger one, where researchers had thought there was one. Other ancient dog burials date to about 11,600 years ago in the Near East, about 8,500 to 6,500 years ago in Scandinavia and about 8,000 years ago in Illinois. A 2018 study found that the younger Bonn-Oberkassel puppy probably caught canine distemper at about 19 weeks old and had two or three periods of serious illness lasting five to six weeks. A study author said the puppy was too sick to be a working animal, which suggests people cared for it for something other than its use. A museum curator on the study said that at least some Paleolithic people saw dogs not just as useful but already had a strong emotional bond with them.
Words to know
- domesticated: tamed over time
- pheromone: chemical signal
- brachycephalic: short-skulled
- Paleolithic: Stone Age
- oxytocin: bonding chemical
