People still argue about when, where and how dogs were domesticated. 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. Where dogs first appeared is hard to say. It could have been in the Middle East, China, Siberia or several places at once. 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.

The scavenger hypothesis says wolves that were less afraid of people lived near villages and ate scraps from garbage piles. Over time, it says, they became dogs. One idea about how dogs began is that calmer wolves hung around people's camps to eat leftover food. Other ideas say people trapped wolf pups on purpose to train them as sentinels or hunters. Another says wolves and people helped each other, with people learning to hunt by watching wolves. An evolutionary biologist who studies dog origins said there are as many scenarios for how dogs began as there are people working on it, because it was so long ago.

Dogs have lived with people for at least 14,000 years. A puppy buried with two people about 14,000 years ago had been sick for weeks, and people took care of it. The researchers who re-examined the grave said the sick puppy would have been kept warm and clean. They said it would have been given water and probably food. That suggests a relationship of care 14,000 years ago. The puppy probably could only have survived thanks to long and intensive human care, the study's authors said, because distemper is a life-threatening sickness.

Scientists chose Siberian silver foxes for a farm-fox experiment because they are close genetic cousins of wolves. In it, Dmitri Belyaev asked Lyudmila Trut to lead an experiment with foxes, which are closely related to dogs. The aim was to see how domestication unfolded and which evolutionary forces were at work. Trut tested each fox by seeing how it reacted when she approached its cage, opened the door and put in her gloved hand. 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 many generations the foxes acted like friendly dogs.

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. Owners whose dogs gazed at them longest had the biggest rises in oxytocin. Another study, at Duke, looked at puppies: it used 44 dog puppies and 37 wolf puppies, 5 to 18 weeks old, to test 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. A third line of work followed Chaser the border collie, who was trained by retired psychology professor John Pilley starting in 2004. He showed her 1,022 objects in total.

A dog's sense of smell is far, far stronger than a person's. 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. 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. This helps bring in new smells and lets dogs sniff almost continuously.

Dogs also have a vomeronasal organ, also called Jacobson's organ, a second smell system we do not have, built for chemical communication. Its pheromone signals go to their own part of the brain, so they do not get mixed up with ordinary smells. A dog's nose has more than 100 million smell receptors, while a person's has about 6 million. Scientists have estimated that dogs smell thousands of times better than people, though the estimates vary a lot. A dog researcher wrote that a dog could detect a teaspoon of sugar in a million gallons of water, about two Olympic-sized pools.

Guide dogs help people who are blind get around. Morris Frank read about dogs trained to guide blinded veterans of World War I in 1927. 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. Other dogs search for people. 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.

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 it, 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. They found 12 of the 14 breeds had some breathing abnormality. Flat-faced dogs also have a harder time cooling off than other dogs.

A wagging tail or a crouching body does not always mean a dog is friendly. 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. If a dog you do not know comes up to you, stay still and quiet instead of running. Even a friendly family dog can snap if it is startled, so give dogs their space. Some dogs show they are scared or angry before they bite, so stay away from any dog that growls or backs away.

Words to know

• hypothesis: a testable idea
• scavenger: eats leftovers
• oxytocin: bonding chemical
• turbinates: scroll-like bones
• brachycephalic: short-skulled