The extraordinary story of the species that became our allies.
Dogs became our companions
Wheat fed a booming population
Cattle gave us meat and milk
Maize fuelled the growth of empires
Potatoes brought us feast and famine
Chickens led us to wonder about tomorrow
Rice promised us a golden future
Horses gave us strength and speed
Apples travelled with us
HUMANS TAMED THEM ALL
For hundreds of thousands of years, our ancestors depended on wild plants and animals to stay alive – until they began to tame them.
Combining archaeology and cutting-edge genetics, Tamed tells the story of the greatest revolution in human history and reveals the fascinating origins of ten crucial domesticated species; and how they, in turn, transformed us. In a world creaking under the strain of human activity, Alice Roberts urges us to look again at our relationship with the natural world – and our huge influence upon it.
Alice Roberts is an anthropologist, writer and broadcaster, and is currently Professor of Public Engagement in Science at the University of Birmingham. She has presented several landmark BBC series including The Incredible Human Journey, Origins of Us, Coast and The Celts. Her latest book on evolutionary biology, The Incredible Unlikeliness of Being, was shortlisted for the Wellcome Book Prize in 2015.
‘Lyrical storytelling untangles the current thinking on how we’ve entwined our lives with those of plants and animals. From dogs to apples to potatoes to chickens, Roberts provides fascinating insights into domestication, offering anecdotes from past and present that link genetic and archaeological findings.’
BBC Wildlife Magazine, Book of the Month
‘Superb: fascinating, intimate biographies of the species that have shared our white-knuckle ride to the present and have helped to make us what we are. Read if you want to know what and why you are.’
Charles Foster, author of Being a Beast
‘Roberts remains composed, engaging and undogmatic throughout … Tamed is an excellent point of entry for anyone who wants to understand the new deep human history.’
Peter Forbes, Guardian
ALSO BY ALICE ROBERTS
Don’t Die Young: An Anatomist’s Guide to Your Organs and Your Health
The Incredible Human Journey
The Complete Human Body
Evolution: The Human Story
The Incredible Unlikeliness of Being: Evolution and the Making of Us
The Celts: Search for a Civilisation
To Phoebe and Wilf, who love the wild places
‘HEAR and attend and listen; for this befell and behappened and became and was, O my Best Beloved, when the Tame animals were wild. The Dog was wild, and the Horse was wild, and the Cow was wild … and they walked in the Wet Wild Woods by their wild lones …’
Rudyard Kipling, ‘The Cat That Walked By Himself’
For hundreds of thousands of years our ancestors existed in a world where they depended on wild plants and animals. They were huntergatherers – consummate survival experts, but taking the world as they found it.
Then the Neolithic Revolution happened – at different times, and in different ways, in different places – but across the globe, those hunter-gatherers were changing how they interacted with other species in a crucial fashion. They tamed those wild species – and became herders and farmers. The domestication of plants and animals would pave the way for the modern world – allowing the human population to boom, and the first civilisations to grow up.
By uncovering this deep history of familiar species, we’ll discover just how important those plants and animals were – and are – to the survival and success of our own species. These others have teamed up with us, and are now found right around the world, and have changed our lives immeasurably. We’ll dig back in time to trace their – sometimes surprising – origins. But we’ll also find out how becoming part of our world changed those plants and animals, as we tamed them.
When the Victorian scientist Charles Darwin set about writing On the Origin of Species – the foundation stone of evolutionary biology today – he knew he was about to drop a bombshell – and not just into the world of biology. He understood that he had to prepare some serious groundwork before he leapt into explaining his extraordinary insight into how species changed over time, through the unthinking action of natural selection, working its magic, generation by generation. He needed to bring his readers along with him. They’d be climbing a mountain together; it would be fraught with difficulty, but the view from the top would be stupendous.
And so Darwin refrained from jumping straight into explaining his revelation. Instead, he devoted an entire chapter – a whole twenty-seven pages in my edition – to describing examples of species evolving under the influence of humans. Within a population of plants or animals, there is variation – and it’s by interacting with that variation that farmers and breeders are able to modify breeds and species, generation by generation. Over hundreds and thousands of years of humans promoting the survival and reproduction of some variants, and limiting the success of others, our ancestors had wrought change in domesticated species and strains, moulding them until they more neatly fulfilled human needs, desires and tastes. Darwin called the effect of human choice on those domesticated species ‘artificial selection’. It was an idea that he knew his readers would be familiar and comfortable with. He could describe how selection by farmers and breeders – picking out particular individuals to breed from, discarding others – would, over generations, produce small changes, and that these changes would accumulate over time so that sometimes diverse strains or subtypes would emerge – from a single, ancestral stock.
In fact, this gentle introduction to the power of selection to wreak biological change wasn’t just a literary device. Darwin had set out to study domestication himself, because he believed that it could cast light on the mechanism of evolution more generally – on how wild plants and animals could become gradually modified. He wrote, ‘… it seemed to me probable that a careful study of domesticated animals and cultivated plants would offer the best chance of making out this obscure problem. Nor,’ he added, almost with a glint in his eye, ‘have I been disappointed.’
After discussing the effects of artificial selection, Darwin could then go on to introduce his key concept of natural selection as the mechanism behind the evolution of life on the planet, the unthinking process that would, over time, propagate modifications and grind out – not just new strains – but entirely new species.
Reading his book today, the word ‘artificial’ trips us up. Firstly there’s the other meaning of ‘artificial’ – where it’s synonymous with ‘fake’. That wasn’t the sense in which Darwin was applying the word; he meant artificial as in ‘by artifice’. But even then, there’s a knowingness implied by this word which overplays the role of conscious intent in the process of domestication of species. Modern plant and animal breeding may be carried out with careful, deliberate aims in mind, but the earlier history of our liaisons with the species that have become our major allies reveals a shocking lack of any planning.
So we could try to come up with a new word for ‘artificial’, but there’s another problem. Given that we now accept the fundamental role of natural selection in evolution, given that Mr Darwin doesn’t need to persuade the majority of us of this biological reality – do we actually need a separate description for the way that humans have affected the evolution of domesticated species?
Describing artificial and natural selection separately helped Darwin to build his argument, and to introduce a challenging, new idea, but the distinction is actually false. It doesn’t really matter that it’s us humans – rather than the physical environment or other species – that are mediating the assortment of individuals into those more or less likely to successfully reproduce. You wouldn’t make this distinction for any other species. Take the selective pressure exerted by honeybees on flowers – which leads to changes in those flowers over time, making them more attractive to their pollinators. The colours, shapes and scents of flowers are not designed to delight our senses – they have evolved to entice in their winged allies. Have the honeybees been effecting artificial selection? Isn’t this just bee-mediated natural selection? Perhaps, when it comes to our own influence on domesticated species, instead of ‘artificial selection’ it’s better (although, admittedly, slightly clunkier) to think of it as ‘human-mediated natural selection’.
Natural selection works its wonders by weeding out particular variants, while others survive and reproduce – passing genes on to the next generation. Artificial or ‘human-mediated natural selection’ often works in the same way, as farmers and breeders reject certain plants or animals which aren’t as docile, productive, strong, tall or sweet as others. Darwin described this negative selection in the Origin:
When a race of plants is once pretty well established, the seed-raisers do not pick out the best plants, but merely go over the seed-beds, and pull up the ‘rogues’ as they call the plants that deviate from the proper standard. With animals this kind of selection is, in fact, also followed; for hardly any one is so careless as to allow his worst animals to breed.
By pulling up the rogues, sifting out the animals that we don’t want to breed on, or even just looking after certain animals better than others, humans have become powerful agents of natural selection. We’ve roped in a great variety of plants and animals to become our allies in the game of life.
Yet, as we’ll see, sometimes this taming seems to come about almost by accident. And sometimes it appears as though the plants and animals are actually domesticating themselves. Perhaps we’re not as all-powerful as we once believed ourselves to be. Even when we’re setting out deliberately to break in a species, to make it more useful to us, we’re really only unlocking a natural, latent potential to be tame.
The deep histories of plants and animals that are very familiar to us today take us to strange and exotic locations. It’s a good time to be tracing these stories. Arguments have raged on over how each domesticated species sprang into being – from a single origin, a single discrete centre of domestication, or from a wider geographic area, as different wild species or subspecies were tamed and then interbred to form hybrids. In the nineteenth century, Darwin thought that separate wild species could explain the immense variety we see in our domesticates. In contrast, the great, early-twentieth-century plant-hunter and biologist Nikolai Vavilov thought that he could pinpoint discrete centres of origin. Archaeology, history and botany provide plenty of clues, but also leave us with plenty of unresolved questions. With the arrival of genetics – a new historical source – on the scene, we now have a hope of testing competing hypotheses and solving these seemingly intractable puzzles, to uncover the real story of the plants and animals that have become our allies.
The genetic code carried by living creatures contains within it not just the information to make the modern, living organism, but also traces of its ancestry. Looking at the DNA of living species, we can delve into their deep past – thousands, even millions of years back – and glean some clues. We get further insights if we can add genetic clues from DNA extracted from ancient fossils. The first contributions from genetics focused on small fragments of genetic code, but in just the last few years, genetics has broadened its scope to look at entire genomes, and has produced a panoply of surprising revelations about the origins and histories of some of the species closest to us.
Some of those genetic revelations challenge the way that we divide up the biological world. It’s useful – and meaningful – to identify species. That concept embraces a group of organisms that are diagnosably similar to each other – and diagnosably different to others. But the fact that populations undergo evolutionary change, over time, can make drawing boundaries around species quite difficult. We do like to put things in boxes, but biology seems to delight in breaking itself out of such constraints, as we shall learn again and again in this book. How far do lineages have to diverge before they are truly separate species? That’s still a question which taxes taxonomists. When it comes to domesticated animals and plants, some are considered to be subspecies of their wild counterparts, and are given the same species name as their untamed progenitors, and surviving wild cousins – if there are any. Some biologists have advocated using entirely separate species names for domesticates, even if they’re very similar to wild relatives, for ease of reference. The debate over naming shows just how blurred the borderlines are.
In each case, the evolutionary trajectory of the domesticated species – from cattle and chickens to potatoes and rice – was profoundly influenced by becoming intertwined with that of an African ape that had already spread across the world and gone global. These stories are extraordinary and manifold, but I have focused on just ten species. One of those species is us, Homo sapiens. The astonishing transformation we’ve undergone – from wild apes to civilised humanity – suggests that we have somehow tamed ourselves. And only after that happened could we set about taming others. I leave the story of humans to the last chapter. There are many surprises and very new revelations there – hot off the scientific press – but you’ll have to wait for those. Spend time first with nine other species. Each one has had a huge impact on us and our history – and is still important to us today. These domestications are scattered through time and space, so that we’ll understand how human societies have been interacting with plants and animals in various ways, around the world and through history. Their spread around the globe accompanies our own movements – sometimes even fuelling and propelling those human migrations. We find dogs running with hunters; wheat, cattle and rice travelling with the earliest farmers; horses carrying their riders out of the steppe into history; apples stowed in saddlebags; chickens spreading with empires; potatoes and maize crossing the Atlantic on trade winds.
The Neolithic, which first started around 11,000 years ago in East Asia and the Middle East, formed the foundations for the modern world. It was the most important development in the entire history of humanity. We became entangled with other species – in symbiotic relationships that meshed our evolutionary paths together. Farming created the capacity to grow the global human population to immense proportions. Our population is still growing, but we’re pushing at the boundaries of the capacity of this planet to support us. We need to – quickly – develop sustainable ways of feeding at least a billion or two more of us than already live on earth.
Some solutions may be low tech – organic farming has proven much more promising than its detractors suggested, even just fifteen years ago. But high tech may form part of the solution, too. We need to decide how we feel about embracing – or rejecting – the newest generation of genetic modification – tools which can deliver precise genetic adjustments to suit our needs, bypassing the selective breeding our ancestors relied on – or even creating new possibilities that are limited only by our imaginations.
There are other challenges – with a human population that’s still growing, and four-tenths of land already farmed, we need good evidence to show us the best solution for preserving as many wild species as possible. We’re clever – that’s always been a characteristic of humans. But we need to be cleverer than ever if we’re to find a way of balancing the voracious appetite of a growing human population, and the hordes of tame species we need to survive, with biodiversity and real wilderness. It can sometimes feel as though we humans are a plague on the planet, and it would be a complete catastrophe if the real legacy of the Neolithic Revolution was mass extinction and ecological devastation. We have to hope that there might be a greener future for us – and our allies. Scientific research may not only illuminate the history of our interactions with other species, it provides us with powerful tools to inform the future directions that we can choose to take. Knowing more about the histories of our domesticated species will help us plan for the future.
But let’s start with the past, and see where that takes us. We’re going back far into prehistory to begin the journey, to a world unrecognisable today. A world with no cities, no settlements, no farms. A world still in the chill grip of the Ice Age. Where we meet the first of our allies.
When the Man waked up he said, ‘What is Wild Dog doing here?’ And the Woman said, ‘His name is not Wild Dog any more, but the First Friend, because he will be our friend for always and always and always. Take him with you when you go hunting.’
Rudyard Kipling, ‘The Cat That Walked by Himself’
The sun had set and the temperature had dropped even further. These were the cold, hard months, when the day was so short that there was barely enough time to hunt, to mend the tents, to chop wood for the fire. The temperature outside never rose above freezing. Towards the end of winter, things always got difficult. The dried berries from last summer would eventually run out. Then there was meat for breakfast, meat in the middle of the day, meat for supper. Mostly reindeer meat, of course. But occasionally, just for a change, a bit of horse or hare.
There were five tents in the camp: tall and conical, like robust tipis. Each was built on a skeleton of seven or eight larch poles, covered with hides, all stitched together and tied in place against the wind. Under the snow, a ring of stones held the skirt of the tent down. The fallen snow, at least half a metre deep around the sides of the tipi, also helped to keep the hides secure. Between the tipis, the snow was trampled. The remains of a hearth lay in the centre. It was barely used now – during these frozen weeks, it was much better to light fires inside the tents. And so, in each one, a fire blazed in a central hearth. The contrast in temperature was extreme. As the families retreated into their tipis for the night, fur coats and trousers and boots were discarded in a great pile by the door.
Outside the ring of tipis was a place for chopping wood. One or two men would split felled larch trees all day, enough to keep the fires in the tents burning. In another place lay the scant remains of what had been a reindeer. It had been butchered into pieces, and there was little left apart from a few ribs and blood-stained snow. The hunters had killed it that morning, and brought it back to the camp. When they arrived, they had immediately opened up its belly to take slices of still-warm liver to eat, and to drink its blood. The rest was divided up amongst the five families, and carried off into the tents. Apart from the head – once the tongue and cheeks had been removed, the antlered skull had been carried back into the edge of the forest. A young man had taken it, tying it to his belt and climbing several metres up a larch tree before wedging the skull between a branch and the trunk: a sky burial; an offering to the spirits of the forest and the spirit of the reindeer itself.
After another meal of mainly meat, the families started to settle down for the night. Children were tucked up under piles of reindeer skins. The last adult to go to sleep in each tent stacked logs onto the fire. It would burn on for another hour or two. Then the temperature inside the tent would drop, almost to the ambient chill outside. But the reindeer fur would keep them warm, just as it had kept its original owners warm through the icy winters in this cold, northern land.
As the skeins of blue smoke escaping from the tops of the tents grew thinner, and the murmur of conversation died down, that meagre carcass on the edge of the camp drew scavengers out of the forest. Emerging from the taiga – like shadows, skulking and silent – the wolves approached the camp. They made short work of the remains of the deer, and then they prowled around the tents and the central hearth, searching for other scraps, before disappearing back into the trees.
The hunters were used to the proximity of wolves. They even saw a spiritual link with these animals, who were also eking out an existence in these sparse forests on the edge of the true tundra. But this winter, the wolves were more of a constant presence than ever before. They were in the camp every night. In previous years, they had occasionally come near during the hours of daylight – never within the circle of tipis, but close enough. Perhaps they were driven by hunger. Perhaps these wolves had been becoming bolder over years, even generations. Mostly, the humans tolerated them. But stones, bones and sticks were thrown at the wolves if they came too near.
It was at the end of that long, hard winter – surely longer and harder even than the one before – that one wolf, a youngster, came right into the centre of the camp. A girl of about seven was sitting on a log, mending her arrows, and the wolf came very close to her. The girl stopped what she was doing. She laid down the arrows, rested her hands on her knees and looked down at the trodden, compacted snow. The wolf padded a few steps closer. The girl glanced up and down again. Then the wolf came right up to her. She felt the wolf’s warm breath on her skin. Then the wolf licked her hand and momentarily sat back on its haunches. The girl looked up and into the blue eyes of the young wolf. An astonishing moment of connection. And then the wolf leapt up, spun round and bounded away, back into the taiga, back into the shadows.
The wolves seemed to be tracking the people that summer, as they in turn tracked the huge herd of reindeer, migrating in stages across the landscape. The snow melted and gave way to vast expanses of grassland. The reindeer would graze and move on. The people were always just one step behind, striking their camp each time the herd began to shift, setting up again when they were settled. Usually, the wolves would melt away in summertime, as hunting became more profitable than scavenging from human hunters. But these wolves – or at least some of them – had somehow found themselves drawn to the side of the humans, even joining in with the hunts – and profiting from the fallen prey.
It was a nervous, fragile alliance. The wolves were wary of the humans, and the humans of the wolves. There were stories of these predators snatching babies from camps, although no one seemed to have experienced this first-hand. There were tales of hunters bringing down a deer, only for wolves to claim the carcass, driving the human hunters away. The older members of the tribe were suspicious and cautious. But there was no doubt that the wolves had improved the success of the hunts. They could help to separate a reindeer or a horse from the herd, sometimes even bringing the animal down before the hunters got near enough to throw their spears. The wolves would flush out smaller game, too. The hunters rarely came home empty-handed. And so there was less hunger – especially during the tough winter months. More wolves ventured into the camp during daylight, and they didn’t seem aggressive. After a few more winters and summers, parents would even let their children play with the friendly wolf pups, tumbling and play-fighting in the space between the tents. Some wolves started sleeping close to the camp. It was clear that this pack had affiliated itself with the humans. When the tents were dismantled and wrapped up and the people moved on, the wolves moved with them.
Who domesticated whom? Had the wolves chosen the people or the people chosen the wolves? However it began, this alliance would change the fortunes of the humans and it would change the form and behaviour of their canine companions. After just a few generations, the friendliest wolves had started to wag their tails. They were becoming dogs.
This is clearly fiction. But it is fiction based on scientific facts that we can now be very sure of. Our modern dogs, in all their wonderful variety, are the descendants of wolves. Not foxes, jackals, coyotes or even wild dogs. Wolves. European grey wolves, to be precise. Our modern dogs share over 99.5 per cent of their genetic sequences with these grey wolves.
What drew wolves to our side? Archaeologists in the past have suggested that it could have started with the advent of farming. The lure of livestock – easy pickings for opportunistic predators – would have been hard to resist. But the earliest evidence of farming – marking the beginning of a new age for humans, the Neolithic – goes back some 12,000 years to the Middle East. Dog skeletons have been found at archaeological sites much older than this. Of all the animals and plants that have been changed by coming into close contact with humans, forming alliances with us, the dog seems to be our most ancient ally: the first people to have dogs were not farmers, but Ice Age hunter-gatherers. But just how far back into our prehistoric past can we trace that alliance? And where, how and why did it happen?
The traditional story of the domestication of dogs saw this process taking place around 15,000 years ago, at the tail-end of the last Ice Age. This was the time when the ice sheets were retreating northwards, when trees and shrubs, humans and other animals began to colonise the higher latitudes of Europe and Asia once again. The tundra greened, rivers ran full and the sea level rose, as warmth and life returned to the icy north. The ice sheets that had gripped North America from coast to coast also began to retreat, and groups of humans migrated from the vast, continent-like Beringia into the New World.
There’s plenty of definitive evidence of domestic dogs from 14,000 years ago onwards: bones which are clearly those of dogs, not wolves, turn up in archaeological sites across Europe, Asia and North America. Yet there’s a possibility that these are relatively late examples. At the beginning of the twenty-first century, as geneticists started to team up with archaeologists to probe questions about the origin of domesticated species, a suggestion emerged: that the domestication of dogs could have begun much earlier, even tens of thousands of years earlier, than previously thought.
Geneticists began to approach the question of dog origins by looking at patterns of differences in dog mitochondrial DNA to reconstruct a ‘family tree’ for this small package of genes. The results could be interpreted in different ways – the reconstructed family tree was compatible with two, completely distinct models of dog origins. One suggested that dogs arose from multiple origins, around 15,000 years ago. The other fitted with an early, single origin of most dogs – going back 40,000 years. The discrepancy in timing between the models is large – the possible dates are not only separated by thousands of years, but by the peak of the last Ice Age, which climaxed some 20,000 years ago.
Mitochondrial DNA is just one strand, and actually just a tiny part, of the genetic legacy carried inside the cells of an organism. There’s much more information to be found in the chromosomes – the packages of DNA contained in the cell’s nucleus. There are thirty-seven genes in the mitochondrial genome, compared with some 20,000 in the nuclear genomes (of both dogs and humans). When geneticists moved on to the nuclear DNA of dogs, an earlier date started to look most likely. The first draft genome – the genetic sequence contained in all of the chromosomes – of the domestic dog was published in a paper in Nature in 2005. The domestic dog was clearly most closely related to the European grey wolf. The authors (of whom there were – incredibly – over two hundred) had not only worked on a thorough sequence of the dog genome, but had made a start on mapping variation amongst different breeds of dog, looking at where single letters in the DNA sequence varied – at more than 2.5 million positions in the genome. The analysis revealed genetic bottlenecks linked to individual breeds – in other words, the dogs’ DNA showed how each breed had started off with a handful of individuals, taking in just a fraction of the genetic variation that had existed across the species as a whole. Each breed represented just a small sample of that variation. Those bottlenecks, linked to the origin of different dog breeds, are really quite recent, probably happening around thirty to ninety generations ago. Assuming an average generation time of three years, that translates into just 90 to 270 years ago. In addition to these more recent genetic bottlenecks, the DNA of modern dogs also held traces of a much more ancient bottleneck: one that was presumed to result from the original domestication of some grey wolves – into dogs. The geneticists estimated that this bottleneck occurred around 9,000 generations ago – around 27,000 years before the present.
This potentially early date for domestication prompted archaeologists and palaeontologists to wonder if they’d been missing something, and one group of researchers set out to examine that possibility. They looked at nine skulls of large canids – animals that could have been either dogs or wolves – from sites in Belgium, Ukraine and Russia, dating to between around 10,000 and 36,000 years ago. They didn’t make any assumptions about whether these skulls did in fact represent wolves or domestic dogs. Instead, they made careful measurements and then compared the data from the ancient skulls with a large sample of more recent canid skulls, including obvious examples of dogs and wolves. Five of these ancient skulls appeared to be wolf. One was impossible to pin down. Three were closer to dog than to wolf. Compared with wolves, these canids had shorter, broader snouts, and slightly wider braincases. One of these ancient dog skulls was very old indeed. It was from Goyet Cave in Belgium, which has proven to be a treasure trove of Ice Age artefacts, including shell necklaces and a bone harpoon, as well as bones from mammoth, lynx, red deer, cave lion and cave bear. The cave had clearly been used by humans and animals for thousands – perhaps even tens of thousands – of years. But it was possible to pin a precise date on the putative dog skull, using radiocarbon dating. It was around 36,000 years old – the oldest known dog in the world.
What was particularly interesting about Goyet was that this early dog had a skull shape that was quite distinct from that of a wolf. The palaeontologists who carried out this study argued that this distinct ‘dogginess’ suggested that the process of domestication – or, at least, some of the physical changes associated with it – may have been very rapid. And once skull shape had changed – from wolf-like to dog-like – it stayed that way for thousands of years.
And yet this is a single example of what looks like an early dog, dating from before the peak of the last Ice Age. It’s so surprisingly early that it seems sensible to consider the possibility that Goyet is an aberration of some kind. Even if the dating can be trusted, couldn’t this just be a weird-looking wolf? Goyet, however, was soon joined by another, apparently very early dog. In 2011, just two years after the publication of the analysis including Goyet, a group of Russian researchers published evidence of what looked very much like another ancient dog, this time from the Altai Mountains of Siberia.
The Siberian skull was found in Razboinichya (Bandit’s) Cave – a limestone cavern tucked away in the north-western corner of the Altai Mountains. Excavations starting in the late 1970s and continuing until 1991 turned up thousands of bones, buried in a layer of red-brown sediment deep inside this cave. Amongst the bones were those of ibex, hyena and hare – and a single, dog-like skull. No stone tools were found in the cave, but some flecks of charcoal suggested that ancient people had also visited it during the Ice Age.
In the initial analysis, a bear bone from the fossil layer in Razboinichya Cave was radiocarbon dated to around 15,000 years ago – the late Ice Age. All the other bones were assumed to be of a similar age. So that dog skull could have been boxed up and swiftly forgotten about, languishing on a dusty shelf in a university or museum storeroom – yet another example of a dog from the tail-end of the Ice Age, when the world was warming up again.
But Russian scientists decided the skull deserved more careful scrutiny. Firstly, was it really a dog? The Razboinichya skull – which quickly acquired the nickname of ‘Razbo’ – was measured and compared with the skulls of ancient European wolves, modern European and North American wolves, and the crania of much more recent dogs, from Greenland, from around a thousand years ago. Those Greenlandic dogs were of a large but ‘unimproved’ type – they hadn’t gone through the genetic mill of extreme selective breeding that would produce all the weird and wonderful variety seen in modern dog breeds. Razbo was a tricky beast to pin down. Like Goyet, its snout was relatively short and broad – a dog-like characteristic. But it had a hooked coronoid process – the projection of bone on the upper mandible where an important chewing muscle, temporalis, attaches – that was more wolf-like. The length of the upper carnassial tooth – a slicing type of tooth, useful for shearing through muscle and sinew – fell within the range for wolves. But this tooth was relatively short compared with other teeth in Razbo’s mouth: it was shorter than two molars stacked together – and that’s a more dog-like characteristic. The lower carnassial tooth was smaller than that seen in modern wolves, but on the other hand, it fitted comfortably into the range for prehistoric wolves. The teeth were less crowded in the jaw than might be expected for a dog. Despite the short snout, then, Razbo’s teeth looked more wolf-like than dog-like. Yet Razbo’s skull measurements told another story – the skull shape was closer to the Greenland dogs than anything else.
Of course this was always going to be tricky. Early dogs are only just not-wolves. And while some features of anatomy and behaviour do arrive in package form, often because they depend on just a few genes, most traits will appear in a gradual, piecemeal fashion. The transformation occurs over generations: pieces of the mosaic change, little by little, until the picture is a new one. This is why Goyet was quite remarkable – two distinct changes to skull shape, in the form of a broader snout and a wider braincase – do seem to have appeared very quickly in early dogs. But we shouldn’t be alarmed at the discrepancy between skull shape and teeth in Razbo.
With a skull shape like that of a Greenlandic dog from a thousand years ago, but slicing teeth more like wolves, the Russian scientists concluded that Razbo could well have been an incipient dog – one of the earliest examples of this particular experiment in domestication. But still, a 15,000-year-old incipient dog isn’t much to bark about. There are plenty of those knocking around. It was the new dating of the skull – direct dating, using bone samples from Razbo itself, and carried out in three separate labs, in Tucson, Oxford and Groningen – that caused a stir. The skull turned out to be around 33,000 years old. Goyet was no longer alone.
Case closed, then: both bones and genes seemed to be pointing to an early date of domestication, around 30,000 years ago, give or take. Rather than being anything to do with the onset of agriculture (at its earliest, some 11,000 years ago in Eurasia) or even the changing environment and society as the Ice Age released its grip (some 15,000 ago) – it looked like humans’ best friend had much earlier origins: way back in the Palaeolithic, before the peak of the last Ice Age, before anyone lived in villages, towns or cities. When we were all still nomads, hunters and gatherers. Long before our ancestors settled permanently in the landscape.
But, unfortunately, the origins of the domestic dog were also far from settled. In 2014, another team of geneticists weighed in to the debate. Various researchers had argued for origins of dog domestication occurring in Europe, East Asia or the Middle East. So the geneticists wanted to look more carefully at the geographic origin of dogs – and to probe the question of whether a single origin or multiple origins was most likely. They sequenced the genomes of three wolves – from Europe, the Middle East and East Asia – as well as an Australian dingo, a basenji (descended from hunting dogs in western Africa) and a golden jackal. The researchers found plenty of evidence of interbreeding between different canid groups, which somewhat confused the issue. Several dog breeds contain traces of quite recent interbreeding with wolves – freely roaming village dogs, for example, probably had fairly regular contact with wild wolves. However, the geneticists were able to sift through the DNA data, looking past these more recent interbreeding events and searching for clues about the earliest dogs, hidden in the genes of their latest descendants. The genetic evidence pointed to dogs having had a single origin of domestication – and they estimated that this took place between 11,000 and 16,000 years ago. This still suggested that the domestication of dogs wasn’t linked to the advent of farming, as some researchers had previously suggested. Yet on the other hand, this later date was well after the peak of the last Ice Age, leaving Goyet and Razbo stranded on the other side, deep in time.
But then, these Ice Age dogs had always been controversial. Some researchers had called into question the canine credentials of these animals – they seemed so out of step with the rest of the archaeological evidence. The physical differences between these contentious canids and wolves are, admittedly, quite subtle, and doubts were cast on the methods used to analyse and interpret the skulls. The size of the Goyet canid was considered problematic. With such a large skull, it must have had a large body, too – and domesticated animals are generally smaller than their wild counterparts. So perhaps, some researchers argued, it was just another, now-extinct, variety of wolf, rather than a dog. Or, if Goyet and Razbo really were early dogs, they were probably dead-ends – blips, failed experiments in domestication. The bulk of the archaeological evidence still pointed to the true ancestors of our modern dogs being domesticated much later, after the peak of the last Ice Age. A later date would also go some way to explaining the extinction of Ice Age megafauna, such as woolly mammoth and woolly rhinoceros – hunted to extinction, perhaps, as humans teamed up with their deadly canine companions. The objections to the dogginess of the Goyet Cave canid seemed almost too shrill, too indignant: these early ‘dogs’ just didn’t fit with the current edifice of theory; even if they were dogs, they were unlikely to represent the ancestors of our modern hounds. Research into canine domestication is fraught with controversy. If you will forgive me, canine palaeontology is a dog-eat-dog world.
Neither the bones nor the DNA were producing a clear-cut answer, though – in early 2015 it looked as though the weight of evidence was building for a late date of domestication, after the peak of the last Ice Age. After all the excitement over Goyet and Razbo, those early ‘dog-like’ skulls could just be odd-looking wolves – or early dogs whose descendants died out.
But the date of domestication at 11,000–16,000 years ago, inferred from the DNA of living dogs and wolves, depended on a few crucial assumptions about mutation rates and generation times. If the actual mutation rates had been slower, or generation times longer, that would push the date earlier – it would have taken longer for the DNA differences seen between modern dogs and wolves to accumulate.
June 2015 saw the publication of a striking new piece of genetic evidence. This time, rather than sifting through the genomes of modern dogs and wolves, looking for clues to their ancestry, the geneticists had gone after ancient DNA. The transatlantic team, with members based in Harvard and Stockholm, worked on a rib discovered on an expedition to the Russian Taimyr Peninsula in 2010. The rib was clearly canid, and it dated to 35,000 years ago. Sequencing a tiny section of mitochondrial DNA, the researchers were able to identify the species of the animal to whom this bone had belonged – it was from a wolf. The next part of the investigation involved comparing the ancient genome of the Taimyr wolf with genomes of modern wolves and dogs. The degree of difference between the ancient and modern genomes just didn’t tally with previously assumed rates of mutation. Applying the standard rates to the genetic difference between modern wolves and the Taimyr wolf suggested that the common ancestor of both of them lived 10,000–14,000 years ago – but that’s less than half the actual age of the Taimyr wolf. So mutation rates must have been less than had been previously thought – 40 per cent of the assumed rate, or even slower. Using the new, low rate of mutation, the predicted date of divergence of wolves and dogs moves from 11,000–16,000 years ago to 27,000–40,000 years ago.
The revelations didn’t stop there. The geneticists went on to scrutinise particular patterns of variation in the DNA of modern dog breeds – looking at mutations which each involved a single nucleotide ‘letter’. These genetic variants are known as single nucleotide polymorphisms, or – more snappily – SNPs (pronounced ‘snips’). These single-letter mutations are good indicators of evolutionary history in the genome because they’re common – and often inconsequential, so not weeded out by natural selection. Comparing a handful of SNPs (170,000, to be precise) between modern dog breeds and the Taimyr wolf, the geneticists found that some breeds had more wolf in them than others. This suggests that, after the origin of domestic dogs, some populations had interbred with wild wolves. Breeds that had ended up with a bit more wolf in them included the Siberian husky, Greenland sledge dog, the Chinese Shar-Pei and Finnish spitz. The geneticists also looked at the genetic diversity of modern wolves, and found that the split between North American and European grey wolves must have occurred after the Taimyr wolf lineage had peeled away – but presumably before the sea levels rose at the end of the Ice Age, submerging the Bering land bridge that had – during the glaciation when the sea level was low – provided a link between north-east Asia and North America.
So have Goyet and Razbo been saved, then, by the latest genetic research? It seems there’s no reason to doubt the existence of domesticated dogs 33,000–36,000 years ago, nor that their descendants could still be with us today. Genetics, though, has thrown a final spanner in the works here. Goyet’s mitochondrial DNA is unusual – distinct from that of both wolves and other dogs, ancient and modern. So we’re left wondering what Goyet actually was – an early experiment in domestication that led nowhere? Or an unusual, ancient type of grey wolf that no longer exists today? A sophisticated analysis on the 3D skull shape of the Goyet Cave canid, published in 2015, suggests that it’s more wolf-like than dog-like after all. And so the argument continues. Razbo, on the other hand, appears to fit nicely into the dog side of the mitochondrial DNA family tree. So it looks as though Razbo really could have been an early dog – he certainly has plenty of close relations alive today, in the form of our current canine companions.
It’s just incredible how heated the debate over the origins of dogs has been over the last few years. New techniques and new discoveries seem to have the potential to radically change theories. And the story keeps changing. But with all the progress – from better dating of archaeological finds, to faster DNA sequencing – the real history of the origin of our oldest and closest ally seems to be emerging from the shadows at last. And it’s bound to be complicated. Just look at how convoluted the human history that we know about is. When we approach prehistory – our own or the unwritten histories of other species – we may start off very naively, somehow expecting a simple story that neatly summarises the complexity of interactions over thousands of years. It’s no wonder the picture changes as more scientific analyses are carried out and more detail emerges. The work done on the DNA of the Taimyr wolf and its cousins, ancient and modern, shows just how tortuous tracing the roots of domestication can be.
Having pushed the origin of dogs back into the Ice Age, the next question that emerges is – where were dogs domesticated? And was there a single, discrete area where domestication first began, then spread – or multiple times and places where wild wolves became dogs? This might be impossible to pin down – the domestication of dogs may have started 40,000 years before the present, and interbreeding with wolves continued long after that, and can still happen today. But, armed with the latest genetic techniques, which allow us to unlock secrets from genomes, ancient and modern, we can at least try.
The debate over the date of domestication has rumbled on, but pinpointing the area where dogs were first domesticated is no less fraught with contention. On the one hand, the genetic results are unequivocal: dogs are clearly domesticated grey wolves. But the grey wolf has a huge range – right across most of Europe, Asia and North America today, and its geographic range was even wider in the prehistoric past. So where within the huge territory of grey wolves did the alliance with humans first take off? We can quickly eliminate North America – humans arrived too late, after the last glacial maximum, for the original transformation of wolf into dog to have occurred there. Analysis of wolf and dog genomes provides further evidence that dogs must have evolved from wolves in Eurasia. The family tree of canine genomes reveals an early branching event when North American and Eurasian wolves diverged away from each other, and a later divergence – of Eurasian wolves and dogs. Across the Eurasian range of grey wolves, it’s been very much up for grabs: Europe, the Middle East and East Asia have all been put forward as the original homeland of our canine allies.
Geneticists – and by now, you won’t be surprised at this – have argued and argued over this particular question. Early analysis of mitochondrial DNA pointed to a possible – single – origin in East Asia. This seemed to be supported by a peculiar shape of part of the mandible that was shared by both Chinese wolves and modern dogs. Genome-wide analyses also seemed to support a single origin, but were less clear about the site of domestication for a while, as wolves from all over Eurasia seemed to be equally related to our modern dogs. Further work on mitochondrial DNA of living dogs from across the world then appeared to settle the question. It revealed what appeared to be a clear connection between all modern dogs and the ancient dogs and wolves of Europe. This seemed to match the archaeology. The bones of ancient dogs have been discovered in East Asia and the Middle East, but the earliest of them dates to just 13,000 years ago – whereas there are prehistoric dogs from Europe and Siberia ranging from 15,000 right back to over 30,000 years ago. The original ancestors of dogs were, most likely, Pleistocene – Ice Age – wolves from Europe.
In 2016, new evidence came to light. Firstly, there was a careful analysis of the part of the mandible that had been thought to indicate a link between Tibetan wolves (Canis lupus chanco