Dogs have been selectively bred for thousands of years, sometimes by inbreeding dogs from the same ancestral lines, sometimes by mixing dogs from very different lines. The process continues today, resulting in a widening in appearance without speciation, "from the Chihuahua to the Great Dane."
Though groups like the American Kennel Club make very specific designations about breeds and breed hybrids, there continue to be new breeds and breed variants developed all the time, as well as "up and coming breeds" not officially recognized by kennel clubs and experts. (Many dogs not purchased directly from breeders are also mixed-breeds of some kind, or have less than purebred ancestry.)
Dog breeds are dogs that have relatively uniform physical characteristics developed under controlled conditions by humans, with breeding animals selected for phenotypic traits such as size, coat color, structure, and behavior. The Fédération Cynologique Internationale recognizes 337 pure dog breeds. Other uses of the term breed when referring to dogs may include pure breeds, cross-breeds, mixed breeds and natural breeds.
Dogs can either serve as watchdogs or guard dogs or both. A watchdog s job is to bark and raise the alarm when a stranger enters your property. Their job is to warn you. Many small dog breeds make great watch dogs. Whereas a guard dog s job is to look intimidating and protect his family by keeping intruders out. Some breeds are great guard dogs but not great watchdogs. And vice versa. And a few breeds are both great guard dogs and great watchdogs.