When did people start keeping pets? Regardless of when pet ownership began, there is no denying that pets have been harnessed to humans for possibly tens of thousands of years. Today, our attachment to these animals is still going strong with Americans owning approximately 78 million dogs, 85 million cats, 14 million birds, 12 million pocket pets and 9 million reptiles.

Greger Larson is the director of the University of Oxford’s palaeogenomics and bio-archaeology research network. The network is leading a major international project to determine the origins of dogs. According to Larson, the archaeological and genetic record is being studied for evidence of when and how the bond between humans and animals first developed. This is particularly important as it relates to the evolution of human society.

Pets are animals kept for pleasure that have been tamed and domesticated. Not all domestic animals (chicken, pig, cow) are pets, although they can be. Also, not all tame animals (elephant, tiger) are domestic. A domestic animal that has been tamed is kept by people as a source of food, for work or simply companionship. Although scientists are certain dogs were the first domesticated animal, it is unclear if dogs were the first pets kept solely for companionship. “We know that dogs, without a doubt, were the first domestic animal,” says Larson. What animal was the first pet? According to Larson, “The answer to that question is, nobody really knows.”

Larson points out that the story and history of the domestication of pets and their subsequent relationship with humans is not a linear progression from wild to domestic. “These things exist on a continuum,” says Larson. The question regarding when the first pet came into existence is “a bit like asking when did life begin,” he says.

In 2011, researchers at the University of Maine published a study based on a small dog bone found in ancient human fecal matter that proves dogs were being bred by humans in Texas 9,400 years ago. Although the bone fragment provides the oldest known record of dogs in the New World, scientists at the Smithsonian’s National Museum of Natural History are analyzing dog bones found in Colorado they believe may be 11,000 years old. Larson and his colleagues recently published evidence that dogs have been domesticated twice in history from two separate wolf lines. The first occurred in Europe about 16,000 years ago with the second occurrence in Asia approximately 14,000 years ago.

It is possible that domestication may have happened even earlier. Mietje Germonpre of the Royal Belgian Institute of Natural Sciences is a scientist participating in Larson’s project who has published information indicating that a 32,000-year-old canine like skull found in a Belgium cave was possibly the first dog. “What she has posed is an interesting hypothesis,” says Larson. Through studying the data of nearly 1500 ancient dog and wolf remain DNA samples, Larson’s network hopes to not only solve the domestication mystery, but to also determine when dogs first became “man’s best friend.”

Larson reports that some clues exist as both dogs and cats were buried with humans some 12,000 years ago. Dogs also got special burials around 8,000 years ago. The reasons for these burials and special treatments are unknown.

Small toy dogs were kept by the Romans about 2,000 years ago. Although the dogs primary use at the time may have been black rat control, evidence also suggests the dogs may have also been for companionship. Even a few years hundred years ago the evolution from working animals to domesticated pets is evidenced in Europe in which royalty began making garments with special pockets to keep small dogs. The practice of trading dogs and commissioning of animal portraits in the home is also evident. There is even proof that dogs were being bred for specific aesthetics and behaviors at the time.

This article was adapted from a story by Alicia Ault featured on Smithsonian.com titled “Ask Smithsonian: When Did People Start Keeping Pets?”