The History of Dogs as Pets

— -- In honor of National Dog Day, ABC News looked back at how our furry four-legged companions evolved from feral wolves into our best friends.

It was originally believed the first domesticated wolves appeared around 15,000 years ago in the Middle East. New evidence, however, suggests it was much earlier than that. Swedish geneticist Pontus Skoglund published a study last year in the journal Current Biology, describing his findings of a 35,000-year-old Siberian wolf bone. He concluded that canine domestication may have first occurred 27,000 to 40,000 years ago.

According to genetic studies, modern day domesticated dogs originated in China, the Middle East and Eastern Europe. According to Greger Larson, an archeologist and geneticist, gray wolves were domesticated by humans somewhere in western Eurasia. He surmises people in the East were also domesticating wolves at the same time.

Scientists believe wolves were first attracted to human camps to scavenge for leftover food. Over time, some wolves started traveling with the nomadic humans and a sort of natural selection for domestication occurred, Dr. Stephen L. Zawistowski, science adviser emeritus to the American Society for the Prevention of Cruelty to Animals (ASPCA), told ABC News. Women may have been the first to make these wolves a pet, according to Katherine M. Rogers, professor emerita of English from Brooklyn College, in her book "First Friend." It takes six to eight generations to domesticate a canine, according to a 40-year experiment that began in the late 1950s by Russian researcher Dmitri K. Belyaev.

There’s even scientific evidence supporting the bond between humans and dogs. When people look into each other’s eyes, we bond emotionally and release a hormone called oxytocin. A study led by Nagasawa found that when dogs and people gaze into each other’s eyes, the same hormone is released in both the humans and the dogs.

Dog breeds vary in popularity. In the 1890s, Saint Bernards were the No. 1 breed but since the 1990s, Labrador Retrievers have been the favorite.

Special thanks to Alison Jimenez and Dr. Stephen L. Zawistowski at the ASPCA and Brandi Hunter at the American Kennel Club for their help with the research for this story.