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Even in the Stone Age, humans may have loved their dogs. A reanalysis of a prehistoric dog that was buried with two humans reveals that the animal had experienced several bouts of potentially lethal illness. The fact it survived suggests its owners cared for their dog as a pet.

The Bonn-Oberkassel dog was unearthed a century ago in Germany, alongside the remains of a man in his 40s and a woman in her 20s. All are about 14,200 years old.

The dog probably lived long after dogs were domesticated, as evidence for domestication stretches back at least 32,000 years. But the Bonn-Oberkassel dog is still a key specimen because it is the oldest known dog burial, says at Ghent University in Belgium. That means it can help us understand why dogs were domesticated.

Researchers have often assumed that humans domesticated dogs so they could put them to work. Maybe the first dogs helped us hunt, guarded settlements or were used as pack dogs for transport.

However, Janssens and his colleagues say there is an alternative: that humans domesticated dogs simply because they liked having them as pets.

One sick puppy

Their reanalysis of the dog reveals it had terrible oral health. Although only about seven months old when it died, the dog suffered three periods of severe illness when it was between 19 and 23 weeks, possibly due to a virus that causes canine distemper.

“The first infection would be enough to be lethal to most dogs in the wild,” says Janssens. “Then came two extra bouts, and the probability that the animal would survive without human help is very, very low.”

The researchers argue that the sick puppy could not do any useful work. In fact, keeping it alive was probably an unpleasant burden on its owners: the dog might have had diarrhoea and vomited regularly.

Its survival hints that its owners felt a bond of friendship, just like a modern dog owner. “This is the first time we find [evidence] to suggest that dogs were treated emotionally, without expectation of any benefit,” says Janssens.

Love your dog

Bonds of friendship may have helped drive domestication, says at the Royal Belgian Institute of Natural Sciences. “Wolf pups could have been ‘adopted’ to provide company,” she says. “This raising of wolf pups as pets could have been a stepping stone, together with other motives, on the pathway to the domestication of the dog.”

It’s significant that the dog was buried, says at Pennsylvania State University in University Park. “When you start burying animals, it indicates a special relationship of some kind.”

Nevertheless, Shipman thinks we can’t rule out that the Oberkassel dog was – or could have become – a useful working dog. That might explain why its owners cared for it through its illness.