Dogs evolved from wolves—either grey wolves or another, now-extinct type of wolf—though there is some scientific debate about their exact origin. Genetics suggest that dogs broke off from their wild ancestors between 14,000 and 29,000 years ago and became domesticated through human interactions.

There are over 400 dog breeds, but every variation is a member of the same species, Canis lupus familiaris, and all are related to

Dogs come in all shapes and sizes, ranging from huge Great Danes to tiny teacup Chihuahuas. Dog weights range wildly from 1.8 kilograms (4 pounds) for toy poodles to 104 kilograms (230 pounds) for the largest mastiffs.

Humans used simple forms of genetic engineering to breed dogs for specific instincts and characteristics, and the first domestic dogs were likely bred for hunting.

Today, many people keep pet dogs for companionship and comfort, though there are still many modern jobs for dogs, from providing services to individuals to sniffing out wildlife crime.

Unfortunately, feral dogs can wreak havoc in their local ecosystems, primarily by preying on native wildlife, leading to severe population declines.