Dog

The dog is a furry, four-legged mammal that lives with people all over the world. Scientists call it Canis familiaris. Dogs belong to the same family as wolves, foxes, and coyotes. They come in hundreds of shapes and sizes, from tiny chihuahuas that weigh three pounds to Great Danes that stand taller than a small child when they put their paws on your shoulders.

Every dog alive today, no matter the breed, is descended from wolves. Scientists think the first dogs appeared somewhere between 15,000 and 40,000 years ago. The change probably began when friendly wolves came close to human camps looking for scraps. The tamest ones were allowed to stay. Over many generations, those wolves became dogs. This makes the dog the very first animal that humans ever tamed, long before cows, sheep, or horses.

Dogs have keen senses. Their ears can pick up sounds four times farther away than ours. Their noses are even more amazing. A dog has about 300 million smell cells in its nose. A human has only about 6 million. Dogs use their noses to track animals, find lost people, and sniff out things like bombs, drugs, and even certain illnesses.

People have bred dogs for thousands of years to do different jobs. Border collies were bred to herd sheep. Retrievers were bred to fetch ducks shot by hunters. Bloodhounds were bred to follow scents over long distances. Huskies were bred to pull sleds across the snow. Today there are more than 200 official dog breeds, and each one was shaped by humans to fit a purpose.

Dogs are also famous for their bond with people. They can learn hundreds of words and hand signals. A border collie named Chaser learned the names of more than 1,000 different toys. Dogs read human faces, follow where we point, and notice when we are sad. Scientists have found that dogs and their owners release a chemical called oxytocin when they look at each other. It is the same chemical a parent and baby release when they bond.

Dogs work for humans in many ways. Service dogs guide people who cannot see. Therapy dogs visit hospitals and schools to cheer people up. Police dogs help catch criminals. Search-and-rescue dogs find people trapped after earthquakes. Sled dogs still pull teams across frozen parts of Alaska and Canada.

There are about 900 million dogs on Earth. Some live in homes, some live on farms, and some live on the streets. Wherever humans have gone, dogs have followed. The friendship between our two species is older than farming, older than writing, and older than cities.