A dog (Canis lupus familiaris) is a domesticated subspecies of wolves that has been trained to perform tasks for humans. Over thousands of years, simple forms of selective breeding have accentuated instincts and characteristics that make dogs a good fit for hunting, herding livestock, pulling sledges in the snow, and guarding properties. Dogs are also used as companions, and in a variety of other roles including therapy, assisting police and the military, and providing security and comfort for people.
There are more than 400 different breeds of dog, but no two dogs are exactly alike. Their differences are visible in their body shape, facial expressions, and vocalizations, as well as in the way they walk, smell, and mark their territory. Dogs have excellent hearing and sight, powerful jaws that house 42 teeth, and can distinguish up to 10 distinct scents from other canids such as coyotes.
As a result of the humanization of dogs, they are a highly adaptable species and can live in a variety of habitats. Their sense of smell is 10,000 to 100,000 times more sensitive than ours, and they can detect drugs and explosives, as well as locate injured or lost people. They have a profound impact on their human owners’ lives, reducing stress, encouraging movement and exercise, and promoting socialization with other dog owners and pets. In addition, they can lower blood pressure and help a person feel less anxious by raising levels of the hormone oxytocin.