What about apples? I don’t suppose that any civilisation would have crumbled without them, though fruits that can be stored through the winter are few and far between – the lack of apples as a fallback food may have had some impact. We’d still have cider, because we can make that with wild crabapples, and still do. But the wonderful mythology of the apple would be missing from our culture.
Without dogs to help them hunt, perhaps the modern humans of Europe and northern Asia would have been hit even harder by the chilly climax of the last Ice Age, 20,000 years ago. Without wolfhounds to help us hunt out the last wolves, those predators might just have clung on in Britain and Ireland to the present. Might some of the larger, Ice Age megafauna of Europe have survived to the present day without the lethally effective human–dog alliance pitted against them? Without dogs, perhaps there would even still have been small herds of mammoth roaming in northern Siberia today.
Chickens, as we know, joined the party relatively late – domesticated in the Bronze Age – but then raced into the lead as the most important farmed animals on the planet. Without chickens, we’d never have had the Del Marva Chicken-of-Tomorrow Queen. There would have been no cockfighting. The French football team would’ve had to come up with a different emblem. And cuisines around the world would miss the chicken’s flesh and its egg. There are other domesticated birds, certainly, but none so amenable and successful as the chicken. Of course, that may all change when someone launches the ‘Duck-of-Tomorrow’ competition.
Imagining how history would have played out without horses is extremely difficult. From the very beginning, domesticated horses would have had a profound economic impact, vastly extending the range over which herders could tend their cattle on the steppe. Would steppe populations have expanded and pushed westwards and eastwards, as they did, without horses? It seems unlikely.
Horses played a vital role in European prehistory. Out of the steppe on the eastern fringes of Europe came the horse-riders, speaking that language that still echoes today. Language wasn’t their only contribution; the characteristic mounded-up kurgan and timber grave-burial cultures of Siberia and the Pontic-Caspian Steppe spilled over into Europe, too. Picking up an idea which had evolved on the steppe, Bronze Age people around the eastern Mediterranean – as we’ve seen – began to bury their kings under huge tumuli, accompanied by luxuries for the afterlife. Those elite burials often contained horse trappings – and sometimes the skeletal remains of horses themselves. The cult of the horse – inextricably bound up with high status in society – continued into the Iron Age and beyond, and continues to echo in the modern world.
Horses were also used for traction. The first wheeled vehicles probably originated in the steppe, and chariots definitely originated there – around 2000 BCE. Then chariots spread east into China and west into Europe. Warfare was transformed when armies started to fight on horseback, in the second millennium BCE, and cavalry continued to be crucial in battles up to and including the First World War. The global history of conflict would have been vastly different without horses. Cattle can be used for draught, but not for cavalry.
Today, horses may have been largely replaced by wheeled vehicles that travel under their own steam (or combustion), but they’re still admired and valued for their speed, power and beauty. They continue to be entangled with our ideas of high status. Equestrian sports and blue blood are harnessed together.
The loss of cattle from history may seem as though it would be less impactful, but they’ve been critical, not just for meat and milk, but for transport and agriculture – pulling carts and ploughs through the centuries. And they’ve been with us since the early Neolithic – long before horses were domesticated. But, like horses, they became culturally important in a way that transcends their function as beasts of burden and sources of sustenance. Perhaps as such large beasts, in a world where so many megafauna had gone extinct at the end of the Ice Age, they occupied that space in our mythologies. Although domesticated, they symbolised strength, power and danger. The cult of the bull on Crete formed the inspiration for the myth of the minotaur. The mystery religion focused on Mithras, who killed a huge bull, travelled all the way to Britain with the Romans. An image of Mithras is carved into a stone found at one of the forts along Hadrian’s Wall. But cattle didn’t only find their way into our mythology, they influenced our DNA.
Milk and genes
Although Neolithic cows may have been reared primarily for their meat – remember the riddle of the shrinking cow – the use of milk goes right back to at least the seventh millennium BCE. Milk is a fantastic food: it contains a great range of essential nutrients, including carbohydrate, in the form of lactose, lipids and protein, as well as vitamins and minerals – calcium, magnesium, phosphorus, potassium, selenium and zinc. But it’s an unusual food for adult mammals to ingest. Most mammals can’t digest milk as adults. It’s a characteristic of female mammals to produce milk for their young, and – as mammals – we humans have always been well equipped to drink and digest milk in infancy; we’re born expecting to be sustained by our mother’s milk. But the ability to digest milk – in particular, the milk sugar lactose – usually disappears by adulthood in mammals: humans included. The gene encoding the necessary enzyme, lactase, gets switched off. And yet, most of us in Europe can happily drink milk into adulthood.
The domestication of cattle (and sheep and goats) has not only affected our history and culture – it’s affected our biology as well. By starting to keep animals for milk, we altered our environment. We’ve certainly altered the DNA of cattle, through that human-mediated natural selection that we tend to call artificial selection – but by drinking milk, we ended up altering the way in which natural selection was acting on us. Just as we’ve been in the business of remaking other species to suit our needs, tastes and desires – they’ve been remaking us at the same time.
Drinking fresh milk would have presented a real challenge to our ancestors: it would have caused bloating, stomach cramps and diarrhoea in most people brave enough to try it. The problem is caused by that inability to digest lactose, which then stays in the gut and gets fermented by bacteria – leading to all those unpleasant gastrointestinal effects. There is a way of getting around this drawback – and that’s to reduce the lactose content of milk. You can do that by fermenting it or turning it into hard cheese, both of which also preserve the milk in potable or edible form for longer.
As Richard Evershed and his team showed – by analysing the lipids on pottery fragments from Poland – Neolithic farmers there were making cheese, probably from cows’ milk, as early as the sixth millennium BCE. Mares’ milk contains considerably more lactose than cows’ milk – but the invention of fermented milk drinks would have transformed mares’ milk into something which could be safely drunk by anyone. It’s likely that the kumis of the Eurasian Steppe – a mildly alcoholic ‘milk-beer’, still drunk today – was also a very ancient invention.
But some of us have evolved to be able to drink and digest fresh milk quite comfortably, far beyond those early months when we’re dependent on our own mother’s milk. We are ‘lactose tolerant’ – and that comes from possessing an allele, or gene variant, which means we continue producing lactase as adults. The European gene variant linked to lactase persistence is estimated to be around 9,000 years old. In central Europe, early Neolithic populations don’t have the variant; it’s there at a low frequency by 4,000 years ago, but today up to 98 per cent of people in north-western Europe are lactase persistent (or lactose tolerant). This suggests that their ancestors went through times of drought and strife when the ability to digest fresh milk – not just those stored, fermented milk products and cheeses – may have meant the difference between life and death. The gastrointestinal effects of drinking fresh milk – for people who don’t have lactase persistence – were still well known in the first century BCE, when the Roman scholar Varro wrote that mares’ milk acted as a good laxative (if that was the effect you were after), followe
d by donkeys’ milk, cows’ milk, and finally goats’ milk. It seems that lactose tolerance was unusual in Italy even just two thousand years ago. And although it’s now very common in western Europe, lactase persistence is only present in around 25–30 per cent of people from Kazakhstan, for instance.
Descendants of dairy farmers in Africa ended up with a similar adaptation, with the African genetic variant originating around 5,000 years ago, then spreading through the population. These dates fit very well with the archaeological evidence for the origin and spread of domesticated cattle. In contrast, most East Asians – without a history of dairy-farming – are unable to drink fresh milk without severe gastrointestinal side effects ensuing.
Lactase persistence is one of the clearest signs of recent adaptation and evolutionary change in human genomes – apart from the many changes relating to disease resistance. While so many people have been seduced into following a ‘palaeo’ diet, our ancestors’ physiology didn’t stand still when the Neolithic Revolution transformed ancient ways of life. It’s not just the species we’ve domesticated that have changed – they, in turn, have changed us. These alliances have started off in different ways. Some may have begun quite inadvertently, like apple pips deposited in middens and growing into new trees. Some may have been instigated by other species – wolves may have initiated the contact that led to some of them becoming domesticated as dogs. Others may have been more deliberate on our part – the catching and taming of horses and cattle surely fall into this category. But regardless of how they started, each alliance developed into a symbiotic ecological relationship – an experiment in co-evolution. Domestication is a two-way process.
But there’s another curious link between the animals we’ve domesticated and ourselves. We too seem to show some of the traits that appeared when animals were domesticated. Like dogs, and Belyaev’s silver foxes, we’ve ended up with smaller jaws and teeth, and flatter faces than our predecessors, as well as diminished male aggression. This suite of associated characteristics has been called the ‘domestication syndrome’.
The self-tamed species
Humans are extremely sociable, tolerant creatures. We may sometimes forget this when we look at examples of bad behaviour, on the internet, in politics and even in our daily encounters. Worse, criminality, violence and warfare can make us seem like a hopelessly belligerent species. But history shows that we are, on average, less violent today than we were last century, and the centuries before that. We are learning to live together more peaceably, even if we still have some way to go.
If we compare ourselves with our closest living relatives, chimpanzees and bonobos, we come out extremely well. In other apes, large social groups tend to tear themselves apart, while fear and stress are natural responses to meeting an unfamiliar member of one’s own species. Somehow we’ve managed – most of the time – to endure living in very close proximity to many other humans, to react calmly to encounters with strangers, and to cooperate to an extraordinary extent on shared projects. Indeed, our peculiar success as a species, and the development of our extraordinary cumulative culture, rests on that ability to cooperate and help each other. To achieve that, we’ve had to become – tame.
Our species emerged at least 300,000 years ago, in Africa. It’s likely that the ability for symbolic behaviour, including art and spoken language as forms of communication, was present right from the beginning in Homo sapiens, and may even have been present hundreds of thousands of years before, in the common ancestor of us and Neanderthals. After sporadic flashes of symbolic behaviour in the archaeological record – the odd pierced shell, the odd piece of ground-down ochre – it really bursts on to the scene after 50,000 years ago. From then on, we see a great diversity of the types of objects that humans are making; and they begin to make so much art that some of it survives through to the present day – in the form of carved ivory animals and figurines, and painted caves. Anthropological studies into the spread of culture through Tasmania and Oceania hold a clue as to what it was that unlocked all that creativity. If the analogy holds, it’s likely that Ice Age culture blossomed as populations reached a large enough size, with enough mobility and connectedness, for ideas to emerge, take hold, spread and evolve.
Still, increases in population density present a particular challenge for any species. More people means more mouths to feed; there’s more competition for resources. It’s argued that the emergence of ‘modern human behaviour’ – all that cumulative, cultural complexity – would only have been possible with exceptionally high levels of social tolerance. When we’re less afraid, less antagonistic and more open to communication from others – we learn.
Selecting against aggressive tendencies in other animals, from silver foxes to mice, causes widespread changes in behaviour. As you might expect, they become much more friendly. But the changes in behaviour, mediated by hormones, are also accompanied by physical changes – particularly in the shape of the head and face. Tamed silver foxes, as well as displaying patches of white in their coats, have smaller canine teeth and smaller skulls with shorter snouts. The tame adults look like wild juveniles.
Over the last 200,000 years, human skulls have also changed, becoming less robust, with less pronounced brow ridges, thinner bones overall, and less of a difference in the size of canines between males and females. This looks like a similar pattern to that seen in silver foxes and other domesticated animals. The change may be linked to a reduction in testosterone levels – which affects bone growth as well as behaviour. Testosterone produces particular effects at different stages of development. Individuals who’ve experienced relatively high levels of testosterone in the womb tend to have smaller foreheads, broader faces and more prominent chins. Males with high levels of testosterone at puberty tend to develop a taller face shape and a heavier brow. Men with very ‘masculine’ faces like this are perceived to be more dominant.
Looking at early fossils of modern humans, they are generally much more heavy-browed than more recent examples, but is it possible to be more specific about when the changes actually took place? A team of evolutionary anthropologists in the US decided to find out, measuring and comparing samples of skulls – some dating to 200,000 and 90,000 years ago, some from after 80,000 years ago, and a large sample of more recent specimens, dating to within the last 10,000 years. They found that brow ridges were much more pronounced in the skulls dating to more than 90,000 years ago, compared with later samples. The height of the face was also taller in the older sample. The ‘feminisation’ of face shape continued into the Holocene. It’s possible that these changes in face shape were mediated by changes in testosterone levels. If so, then more gracile, feminine skulls – in both sexes – could be a by-product of selection for social tolerance as human populations grew. It’s easy to imagine how that selection pressure might have worked. Evolution is, as geneticist Steve Jones has so brilliantly put it, ‘an examination with two papers’. It’s not enough to simply survive, you must also reproduce – transmitting your genes to the next generation. If you’re a social outcast, you may find it difficult to pass, or even to sit, that second paper. If men with reduced levels of aggression had a better chance of sexual success, then that trait would quickly spread through a population. As human society evolved, and our ancestors began to live more densely, as well as relying on extensive social networks to survive, it seems that we may have – quite inadvertently – domesticated ourselves.
Domesticated animals share another characteristic with us humans – and we’ve taken it to an extreme. We tend to develop slowly. We’re childish, or puppyish, for longer than our wild counterparts. Infants and juveniles are more trusting, more friendly, more playful, and more receptive to learning than adults. If we think about the various scenarios where animals were either tolerated or caught by humans, and then became not only habituated to human presence but cooperative, then it makes so much more sense if we’re talking about juveniles – whether that’s puppies, calves or foals. And if, at ever
y generation, those individuals who grew up more slowly, who stayed receptive for longer, were more likely to continue that alliance with humans, we can see how domestication would have – quite inadvertently – exerted a selection pressure to stay ‘younger’ for longer.
In ‘domesticating’ ourselves, we’ve ended up changing how natural selection acts on us too: favouring those who stay youthful – or at least, behave youthfully – for longer. It seems like a simple transformation. Old hypotheses suggested that ‘neoteny’ was the key here: a sort of arrested development where adult organisms would somehow remain more childlike, both physically and behaviourally. More detailed analyses in biology – and genetics in particular – blows that out of the water. It really never is that simple. Childlike changes are part of it, but they’re not the whole explanation. We’re really only just beginning to understand the conversations that go on between our genes, our hormones, and our environment – including the other species in it. Nevertheless, there is something that may unite all the changes – neural, physiological and anatomical – which are seen in the ‘domestication syndrome’ in different animals. That ‘something’ is a certain population of cells in the embryo which go on to make a great range of tissues in the body – from cells in the adrenal gland to pigment-producing cells in the skin, parts of the facial skeleton and even teeth. The various fates of these embryonic cells – called neural crest cells – seems to map almost too perfectly on to the features of the syndrome. If you had to predict the effects of a defective gene or two involved with neural crest cells, you’d probably say that it would affect particular hormones and behaviour, the shape of the face and the size of teeth, and cause a few interesting changes to pigmentation in the skin. It’s just a hypothesis at the moment, but a good one: it makes predictions which are testable. There should be fewer neural crest cells in the embryos of domesticated animals. And if we start to find some mutations linked to domestication that affect neural crest cells in the embryo, then this could explain the basis of the whole syndrome – and why different mammals display similar changes under domestication. Time – and more research – will tell.
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