Why do dogs and humans have such a special affinity? They tamed each other.
Sharing our lives with animals is a relatively recent human habit. We worshipped, painted, hunted, ate and sacrificed them long before we invited them in to join us by the fire.
Nor do we really know when or how we managed to transform the wolf into the wolf hound curled up at our feet.
The most recent evidence suggests a single domestication event as long ago as 40,000 years ago, but most palaeontologists favour a scenario in which dogs were domesticated in Asia, at least 14,000 years ago, and their lineages split some time before 6,400 years ago into East Asian and Western Eurasian dogs, from which all our modern breeds derive. What this means is that we were living with and using dogs well before the advent of agriculture.
This is important because it tends to support the idea that, rather than humans capturing wolf cubs and ‘taming’ them, wolves domesticated themselves by hanging around human camps and scavenging for scraps.
This theory, known as ‘the survival of the friendliest’, suggests that over an extended period, the friendlier wolves were rewarded with a regular source of food from humans. This rapprochement might have happened quicker than we think. A famous experiment by Russian scientist Dmitri Belyaev in the 1950s showed that, within 20 years, selectively bred wild silver foxes had lost all fear of humans, wagged their tails, developed floppy ears and black and white fur. To all intents and purposes, they had become ‘dogs’.
Once they had been be-friended by them, it didn’t take our hunter-gatherer ancestors long to recognise the value of dogs in tracking, herding and killing prey.
After that, the next logical step was to begin breeding the best animals to preserve and sharpen these natural skills. This was the beginning of individual breeds. The skills a wolf needs, all in one package – aggression, speed, tracking, tearing, digging carrying – were fine-tuned into hounds, terriers, greyhounds and retrievers.
Today, the largest registry of dog breeds to be internationally accepted is the Fédération Cynologique Internationale (FCI) which recognises 339 breeds of dog, divided into 10 groups organised according to purpose, function or appearance.
The dramatic differences in the size and shape of dogs – a Chihuahua and Great Dane can, in theory, successfully mate – is mostly down to us: the result of centuries of selective breeding. Dogs may look very different, but the section of their genome that controls physical traits has been artificially shrunk by this process, creating genetic bottlenecks. These bottlenecks have left some breeds increasingly susceptible to disease and physical deformity (most pedigree bulldogs now require human intervention to mate or give birth). In humans, the opposite is the case, with most inheritable physical traits controlled by the complex interaction of hundreds of genes.
Despite – or perhaps because – they are largely our own invention, our affection for dogs runs very deep.
One further reason may be that we do share a one obvious genetic condition: neoteny. Neoteny means literally ‘stretching of youth’ (from the Greek neos meaning ‘young’, and teínein ‘to stretch’). In the same way that dogs are like wolf cubs that never evolved into adult wolves, so humans are primates who have retained the large heads, flat faces and relatively short arms of baby apes.
In our case, this might have selected for us to grow our brains and develop the skills needed to build complex social relationships. Interestingly, when humans and dogs look into one another’s large, expressive eyes, each of their brains secretes oxytocin, a hormone linked to maternal bonding and trust. This is the only example recorded of such hormonal bonding happening between different species.
There’s one more change – other than the loyalty, affection and stray hair – that dogs may have lavished on us. Over the past 15,000 years, the size of the human brain has progressively shrunk by about 10%. One theory is that, with the rise of civilisation, we have become more sedentary and, as our bodies have become smaller and weaker, so the brain has followed. But another suggestion is this shrinking may be due, in part, to the fact that as we outsourced many of our cognitive hunting skills to dogs – tracking, chasing, herding – we’ve needed less brain capacity to survive.
Under this scenario, dogs and humans have helped to tame each other. Or, to put it another way, dogs have enabled us to find the time to sit, think and create rather than just hunt and gather.
John Mitchinson is a writer and publisher and co-founder of Unbound, the world’s leading crowdfunding platform for books. He was one of the founders of BBC’s QI.