How did a wild animal become a pet? Dogs came from wolves, a very long time ago. They belong to a family of animals called canids, along with wolves, coyotes, foxes and jackals. Dogs have lived with people for at least 14,000 years. But scientists do not agree on when or where dogs were first tamed. One idea about how dogs began is that calmer wolves hung around people's camps to eat leftover food.

Russian scientists bred the tamest foxes with each other. After many generations the foxes acted like friendly dogs. A puppy buried with two people about 14,000 years ago had been sick for weeks, and people took care of it. Dogs have been helping people since ancient times. People have used dogs for hunting, guarding and herding. Search and rescue dogs use their noses to find missing people, including after disasters.

A dog's sense of smell is far, far stronger than a person's. Scientists have estimated that dogs smell thousands of times better than people, though the estimates vary a lot. 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. Dogs use their noses and their eyes to learn about the world around them.

Dogs have two kinds of color cones where people have three. So dogs see blues and yellows well and have trouble telling red from green. Dogs hear sounds as high as about 45,000 hertz, while people top out near 20,000 hertz. Chaser, a border collie, learned the names of more than 1,000 objects, mostly toys. Dogs follow a person's pointing finger to find hidden food, even puppies that were never trained to.

Dogs cool off mostly by panting, not by sweating the way people do. A dog has some sweat glands in its paw pads, but they do little to cool it down. Dogs also widen blood vessels in their ears and face to cool down. A dog's fur coat helps keep it warm in winter. It can help it stay cooler in summer. Flat-faced dogs have a harder time cooling off than other dogs.

Here is how to meet a dog. 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. Even a friendly family dog can snap if it is startled, so give dogs their space.

Words to know

• canids: dog family
• receptors: smell sensors
• cones: color cells
• hertz: a sound unit