A successful alliance between our two species must have depended on a predisposition on both sides – a mutual willingness. Both humans and dogs are social animals, but it must go further than that; after all, there are plenty of social animals that we haven’t teamed up with. Meerkats, monkeys, mice – none of them have ended up domesticated in the way that dogs have. It seemed possible to me that there was something else, something special about wolf behaviour, that could have paved the way for them forming a bond with humans. In order to find out what that might have been, I needed to get close to some wolves.
High on the ridge above the floodplain of the Severn River, a small pack of wolves roams through ancient woodland. There are just five wolves in the pack, all brothers. Two of them are three years old; three are four years old. They are European grey wolves – slender, compact and long-legged. They are more colourful than their name suggests, with russet flanks, black peppering over their lower backs. Their tails are black at the base and at the tip. Their jaws and cheeks are white. Their pointed black ears are fringed with black fur.
The wolves regularly patrol their territory, loping with a springy, trotting gait along woodland tracks, leaping over fallen trees with flowing, effortless ease. When startled, they run faster, breaking into a canter, but then they will settle, finding a clearing to lie in. When it rains, they find shelter in the undergrowth. They eat meat – from horses, cattle, rabbit and even chickens. But they’ve never hunted anything larger than a magpie. They don’t have to, because the humans looking after them provide them with all the meat they need. This is the captive wolf pack that lives at the Wild Place – a rural enclave of Bristol Zoo, out in the wilderness of South Gloucestershire.
I visited the wolves, staying safely on the outside of their enclosure, with one of their keepers, Zoe Greenhill. She knew the wolves very well, working closely with them every day, and was trying to get them used to being transferred to a smaller enclosure where vet checks could be carried out when needed. That was the limit of the training, though; there was no intention to tame these wolves. And although they’d grown accustomed to Zoe’s company, they were still wary of humans in general and easily startled by sudden movements or loud noises. They were also twitchy about new objects in their enclosure; Zoe told me that it had taken quite some time for them to get used to a few newly planted fir trees. I wondered if this group – a small pack of young animals – was particularly nervous, but Wild Place animal manager Will Walker told me that all the wolves he’d ever met had been similarly cautious and shy.
‘I’ve worked with three different packs of wolves in captivity, and I’ve never experienced any wolves that actively approach you and are confident around you,’ he said. ‘We work in the enclosures with them – always two of us at a time, in case anything does go wrong – but the wolves always stay away, at the far end of the enclosure. They’re so nervous of us – sometimes they even regurgitate their food, before running away.’
‘There’s surely a conundrum here then,’ I suggested. ‘If wolves are naturally that cautious around people, how did they ever come close enough to end up becoming domesticated?’
‘Well, they are nervous – and if you confront them, they turn and run in the opposite direction. But you can play with them. If you turn your back on them, and skip around and hide behind trees, on the other side of the enclosure, they all come running, tails up in the air – and they seem really confident. But if you turn to face them – they’re gone again. They’re certainly inquisitive animals – they check out what we’re doing – but they’re not at all bold.’
Of course, it’s perfectly possible that wolves have only become this cautious around humans relatively recently – though even people with spears rather than guns would have posed a serious threat to them in the deep past. Caution was surely a good survival instinct. But there was something else which could make wolves overcome their nervousness.
Will told me how the wolves would also follow the keepers when they carried out their morning checks. As the keepers walked around the fence line, the wolves would trot a few steps behind them on the other side. Curiosity must surely have been what first drew wolves to humans. Nevertheless, while the hunter-gatherers were highly mobile, moving on all the time, that inquisitiveness could only ever have led to brief, sporadic encounters – the opportunity simply wasn’t there to develop an enduring alliance.
This is where changes in the environment may have played a significant role. Some 30,000 years ago in the Altai, the environment was increasingly conducive to human hunter-gatherer communities becoming settled in the landscape. They were still nomads, but they may have stayed in one place for months at a stretch before moving on. Once people began to settle down a bit more, there would have been time for the relationship with wild wolves to develop. Undoubtedly, the meat brought back by human hunters – and the leftover carcasses – would have been a strong attraction. Eventually, then, curiosity and hunger drove the wolves closer and closer to humans, despite their natural cautiousness. And perhaps the nervousness even acted in their favour. Wolves are large, ferocious-looking animals – formidable predators. But if they looked nervous, rather than too bold, perhaps people would have been less frightened, and more tolerant, of them. From cautious contact to tolerance to partnership – gradually, the alliance between the two very different packs, humans and European grey wolves, grew stronger.
At the point when some wolves started to hang out with humans, their future changed and they changed. Wolves who were nervous but friendly would be tolerated. Wolves who were more erratic, perhaps even aggressive, would be driven away or worse. Humans were exerting an evolutionary pressure on the wolves close to them – and the impact of them choosing the friendliest, least aggressive animals would go much further than influencing just that particular facet of their behaviour.
Friendly foxes and mysterious laws
In 1959, the Russian scientist Dmitry Belyaev decided to test out how selective breeding – focusing on specific behaviours – could transform animals over time. He believed that there were fundamental characteristics that were key to dog domestication, that natural tameness would have been positively selected in any wolf cubs, while aggressive tendencies would have been ruthlessly rooted out. He embarked on what has become a famous experiment in domestication, with another species fairly closely related to wolves: silver foxes, Vulpes vulpes. Selecting the tamest foxes in each generation and breeding those foxes together, he and his team found that tameness spread quickly through the population. After six generations of highly selective breeding, 2 per cent of the population were extremely tame. After ten generations, that was up to 18 per cent. After thirty generations, half of the foxes were very tame. By 2006, just about all of the foxes in the ongoing experiment were very friendly towards humans – just like domesticated dogs.
But it wasn’t just the foxes’ behaviour that had changed. While some of them were still silver, others had turned red. That’s still a standard Vulpes vulpes colour – not so surprising. Some, however, had turned white with black markings – the so-called ‘Georgian White’ variety – a complete novelty, never seen in the wild. In fact, the domesticated Georgian White silver fox looks uncannily like a tiny, fox-shaped sheepdog. Some foxes developed a brown mottled colouring, over a silver-white background. Some had floppy ears. And there were changes to their skeletal structure as well, with shorter legs, muzzles and a widened skull appearing. There were changes to reproductive physiology too: wild foxes only mate once a year, but the tame vixens were coming into heat twice, each year. The tame foxes also reached sexual maturity more quickly than their wild counterparts.
Along with the specific attributes of friendliness towards humans, and a lack of aggression, that had specifically been selected for in the experiment, the tame foxes showed other familiar types of behaviour. They held their tails up in the air, and they wagged them. They whined and whimpered to get attention. They sniffed and licked their keepers. They pai
d attention to human gestures and direction of gaze. By selecting for tameness, the Russian fox-breeding scientists had ended up with a host of other characteristics that seemed to have just come along for the ride but which were also undeniably dog-like.
This fox-breeding experiment shows just how quickly the friendliest and least aggressive wolves from thousands of years ago may have become tamer and tamer with each generation. The hunter-gatherers didn’t need to have been selectively breeding like the Russian scientists, following their strict protocol of only allowing the friendliest 10 per cent of their foxes to breed in any generation. The wolf ancestors of dogs could have been self-selecting to some extent – only the friendliest ones would have tolerated living in close proximity with humans. Wolf packs are families, all closely related to each other. If one tended to be tolerant and even friendly to humans, it’s likely that others in the pack would have shared the same genes and behavioural tendencies. So it’s possible that a whole pack, or even most of a pack, could have formed an alliance. Tame wolves would have been able to form an attachment with humans and to start following human social cues such as gestures and glances. Dogs will make eye contact with humans in a way that a wolf would never do. And dogs have evolved to understand human signals in what can seem to be an uncanny way. Having owned a half-trained Border terrier who rarely did anything I wanted him to do, I was recently astonished at the ability of a springer spaniel to understand my cues. I went for a walk with this spaniel, called Linny, on the shore of Loch Long in Scotland. I threw an old ball for her and it went bouncing off amongst seaweedy rocks. Linny didn’t watch it closely enough, and looked at me for some assistance. I shouted, ‘Over there, Linny!’ and pointed, imagining that I would be clambering over the rocks to retrieve the ball, but she followed the line of my point – perfectly – and found the damp ball in a crevice. I was just as pleased as she was, as she bounded back up the beach to drop it once more at my feet. Linny not only recognised that my pointing finger was a referential cue, she knew what it meant, and how to follow this direction to the damp and smelly prize. She was clearly bred from a long line of dogs who had not simply learnt to attend to human cues, but to follow them to an astonishing degree. Springer spaniels are gun dogs, bred for flushing out game and retrieving the quarry. A soggy ball could stand in for a dead duck. Linny was still delighted to bring it to me. Our modern breeds are relatively new inventions – most are the result of highly selective breeding over just a couple of centuries. But although this uncanny ability to understand human gestures has become finely honed in spaniels, the basis of this behaviour is likely to have emerged a very long time ago. The earliest domesticated dogs probably understood human signals – just as Belyaev’s foxes do today.
It seems that domestic dogs – and those domestic foxes – have developed a whole suite of behaviours, as well as anatomical and physiological traits, which seem quite distinct from those of their wild forebears. Yet some of these traits are not entirely novel. I was amazed to learn from Will Walker that wolves occasionally wag their tails and he’d even heard them barking.
‘But I’ve only ever heard them do that as an alarm,’ he told me. ‘There’s an electric fence around the enclosure, and when we first let them in, they were inquisitive and checked it out – touched it – and barked. It just sounded like there was a big dog in there. It was the first time I’d ever heard a wolf bark – but it was a very clear bark. Along with wagging their tails when they’re happy – and all the other traits you see in a dog – it’s all there.’
This seemed to make a lot of sense; after all, dogs are just domesticated wolves. Many of the traits we associate with dogs haven’t just appeared out of nowhere, they were elements of behaviour that were already there in their wolf ancestors. Those traits certainly didn’t feature as prominently in the behavioural repertoire of wolves, but they existed. As wolves were domesticated, certain elements of existing behaviour were selected for or promoted and became more common, while others were selected against and pushed out.
Over time, the relationship between tame wolf and human was changing. This wasn’t just about two species living side by side and tolerating each other. This was symbiosis; the beginning of a beautiful friendship. Humans were no longer just a source of free food, when wolves could get close enough to the camp. Wolves were no longer simply tolerated, they were encouraged: they clearly had something to offer in return for food. That benefit could well have included companionship, for both adults and children. This is rarely mentioned in theories of domestication, perhaps because it seems too frivolous or fluffy, but I think it’s hard to imagine that it didn’t play a role. And surely some wolf cubs would have been adopted. Given how much my own kids clamour for a puppy, it’s not inconceivable that some Ice Age parent would have given in to this pressure.
But companionship, and amusement for children, certainly wouldn’t have been the only benefit of having tame wolves around. Having been a very occasional alarm call amongst wild wolves, a loud bark may have been important in the developing symbiotic relationship between humans and wolves. Maybe those earliest dogs made themselves useful by running with the hunters – helping to track, hunt and even bring back prey. Once farming began, dogs could fulfil a crucial role by protecting livestock from predators such as bears, hyenas – and wolves. But long before that, back in the Ice Age, having tame wolves that could help to protect your camp, and that could sound an alarm by barking, would surely have been very useful indeed.
Barking and wagging tails, then, are not true novelties. We don’t need to invoke some new genetic mutations to explain these traits in dogs, because they already existed in wolves. But even if we can explain away some of the differences between dogs and wolves in this way, there still seems to be too much of a gulf between some of the characteristics of dogs and wolves, or between the traits of wild silver foxes and those of the experimental domestic variety, to be biologically feasible. In fact, the same puzzle also exists when we look at the here and now – at the amount of difference within living dogs today. Their variability is just astonishing: from chihuahuas to chow-chows, Dalmatians to dingoes, the range far exceeds what you see in any wild species.
Darwin was intrigued by the amazing variety of domesticated dogs. He suggested that the diversity could have been drawn from a number of different wild canid species, but we now know that dogs came from a single wild species: the grey wolf, Canis lupus. In a way, that leaves us with an even bigger question about where all the variety amongst modern dogs comes from. In speculating about the generation of diversity, Darwin thought that a lot of variation could be explained by a multiplicity of environmental factors somehow affecting fertilisation or the development of the embryo. Darwin knew that some characteristics were inherited, but he didn’t know how they were inherited. And he was very open to the idea that these environmental factors – nurture, if you will – played an important role.
In the early twentieth century, the work of the nineteenth-century monk and scientist Gregor Mendel – who made great inroads into understanding how traits were inherited – was rediscovered, and formed the foundations for the emerging science of genetics. Combined with the observations of naturalists, and with Darwin’s mechanism of natural selection, genetics helped to explain how evolution worked. The fusion of these separate branches of biology was described in 1942 by Julian Huxley – the grandson of Darwin’s great supporter, Thomas Henry Huxley – in his book Evolution: The Modern Synthesis. But the Synthesis had had a difficult birth.
Huxley described how, at the end of the nineteenth century, Darwinism had dug itself into a rut, becoming overly theoretical and overly adaptationist. Every single character of an organism had to be described as an adaptation, wrought by natural selection. Darwinism had become something approaching natural theology – just that natural selection, not a divinity, was cast in the role of designer. At the same time, new biological disciplines had appeared, including genetics, the study of heredity. Experimental
genetics and embryology seemed at odds with classical Darwinism.
‘Zoologists who clung to Darwinian views,’ wrote Huxley, ‘were looked down on by the devotees of the newer disciplines, whether cytology or genetics [developmental mechanics], or comparative physiology, as old-fashioned theorists.’ But gradually, between the 1920s and 1940s, ideas started to converge – and to make more sense as parts of a whole:
The opposing factions became reconciled as the younger branches of biology achieved a synthesis with each other and with the classical disciplines: and the reconciliation converged upon a Darwinian centre … Biology in the last twenty years, after a period in which new disciplines were taken up in turn and worked out in comparative isolation, has become a more unified science … As one chief result, there has been a rebirth of Darwinism.
The ideas represented by the Modern Synthesis continue to underpin modern evolutionary biology today. We know that the gradual changes which occur within species are essentially due to random genetic mutations. Selection – whether natural or artificial – then acts on those mutations in a non-random way, favouring ones that are advantageous, weeding out any that are not. Still, the variability of domestic species, and of dogs in particular, seems to be just too extreme to be explained only through the accumulation of genetic changes over time – by the simple interaction between random, new mutations in genes and selective breeding. Selection can quickly lead to the spread of advantageous genes (and traits) through a population, but it can’t speed up the underlying rate of mutation.
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