Canines

Kennel societies in the United States recognize 130 breeds of domestic dog, while those in Britain recognize 170 breeds, and the Federation Cynologique Internationale (representing 65 countries) recognizes 335 breeds. The size range of domestic dogs is from about 4 lb (2 kg) to 200 lb (100 kg). Some breeds, such as the dachshund, have short legs, while others, such as the greyhound, have long legs.

For dog owners, these animals can serve a number of different purposes. Pet dogs provide companionship and protection, while working dogs may herd sheep or cattle, or work as sled dogs. Police use dogs to sniff out illegal drugs and to help apprehend criminals. Dogs are also used for hunting and for racing. Guide dogs help blind people find their way around.

Female dogs may reproduce at an age of 7-18 months. Gestation lasts about two months, and the size of a litter is from three to six puppies. Born unable to see, like other canines, domestic dog puppies develop all their senses by 21 days. Around the age of two months, puppies are less dependent on their mother and begin to relate more to other dogs and people. Typical vocalizations of domestic dogs include barking and yelping.

About 10,000 years ago human civilization changed from a gatherer-and-hunter society to a farming culture, and the domestication of the dog began. However, dogs probably also associated with humans before this time. It is believed that all breeds of domestic dogs, whether small or large, long-haired or short-haired, are descended from a wolf-like animal. Breeds of domestic dogs have been produced through selective breeding. One distinguishing feature between domestic dogs and wolves is the orbital angle of the skull. Dogs have a larger angle, which is measured from lines at the top of the skull and at the side of the skull at the eye socket.

The dog, sometimes known as "man's best friend," is treasured by humans. Dog stories abound in children's literature, from Lassie to Rin Tin Tin, and many politicians, including Presidents Franklin D. Roosevelt and Richard Nixon, used dogs to enhance their personal image.

Excessive hunting for their fur or as pests, often coupled with the destruction of habitat, have endangered some species of canines. Their reputation as predators has added to efforts to eradicate them from areas where livestock is raised or where they live close to human settlements. Some of the rare wild dogs, for instance the jackal of Ethiopia, are very few in number. The maned wolf (Chrysocyon jubatus) of Argentina and Brazil has a population of only 1,000-2,000. A successful effort has been made to reintroduce the gray wolf into Yellowstone National Park in the United States, but this is opposed by many local ranchers.