Tamed

by Alice Roberts

  On one such foray, Alyssa and I set off with the women. The children all came along too – infants carried on their mums’ chests in simple cloth slings, toddlers jogging to keep up, the older kids running and skipping. We walked south from the camp for just under a mile, pausing to eat berries on the way. Eventually we all stopped at a dense thicket. The women and children then disappeared inside the bushes, digging around the roots of climbers for tubers. The tubers, which were called ‘ekwa’, were not at all what I had expected – more like swollen roots than the potatoes in my vegetable bed at home. I crawled inside the thicket with a woman called Nabile, who was heavily pregnant – but she wasn’t letting that stop her. She showed me how she dug with a pointed digging stick, and I had a go – it was a useful tool. Breaking up the hard soil and working the ekwa loose with the point, it could then be scooped out with our hands. Nabile would occasionally pause in her digging and take out a knife to sharpen the tip of the stick. We were soon down to the roots of these bushes. Freeing up a section of root from surrounding soil, Nabile would then use the knife again, to cut a piece out – and she’d immediately begin to eat it. These pieces of tuber were about 20 centimetres long and 3 centimetres thick. She’d rip the outer, bark-like layer off with her teeth, then use a knife to make a shallow cut, allowing her to tear off a strip of the root, which she folded up and chewed. She offered me some too. The taste was a pleasant surprise – the first crunch reminded me of biting into a stick of celery, though the taste was completely different. It was quite fibrous, but nutty and moist.

  As well as eating some of the roots raw, where they’d dug them up, the women had each collected a good haul, into their cloth shoulder bags, to take back to the camp. Once there, they got the fires going again and roasted the roots over the embers. I was given a piece to try. Now the skin peeled off very easily, and the flesh inside was much softer – and delicious. It tasted a bit like roasted chestnut.

  Spending just a little time with the Hadza opened my eyes to their way of life – and my own – in a manner that’s difficult to communicate. I came back with a new perspective on my own culture, from how we manage to balance work and family life, to what we eat. It’s all too easy to look at other cultures, in the present and the past, with rose-tinted spectacles, but I still felt that we – in the ‘Western’ world, could learn a lot from these traditional approaches to life. It may not all have been rosy, but with a focus on family and community, there were no ‘jobs’ – and no unemployment. Everyone had a role to play. And children were part of it. There was no suggestion that having children could be detrimental to a woman’s status in society.

  Back to food – I was surprised to see how prized honey was. Men returning with honey were welcomed back more eagerly than those returning with meat. The desire for sweetness is always there – it only becomes a problem when sugar is as cheap and accessible as it is in places like Britain. And as for a varied diet – the Hadza had access to a much broader range of foods than I’d naively assumed, but it was really striking to see just how important roots were in that diet.

  Root and tubers are actually fairly low-quality foods – they have nowhere near the amount of energy that’s packed into fruit and seeds, meat and honey. But they are dependable. Anthropologists asked Hadza about food preferences, and found that honey – the most energy-dense food in nature – came out on top. Tubers consistently ranked lowest. Meat, berries and baobab fruit come somewhere in between. But despite the low ranking of tubers, they’re also the foodstuff that makes up the bulk of the Hadza diet – precisely because they can depend on them. Weighing the separate food types that came back to camp, the anthropologists found that proportions changed from season to season, and also varied for groups in different regions. Tubers appeared to be both a staple food, eaten all year round, and a fallback food – relied on even more when other foods were scarce.

  The fact that most hunter-gatherers in tropical latitudes dig up and eat roots or tubers suggests that humans have probably been doing this for a very long time – perhaps as long as modern humans have been on the planet. That’s more than 300,000 years. But the thick enamel and large teeth of early hominins suggests that this behaviour has even more ancient – forgive me – roots. A simple digging stick could have given our ancestors a vital survival advantage on the plains of Africa. But all of this seems very speculative. These are good hypotheses, certainly, but we need to test them. Is it possible to find any firmer evidence of our forebears eating tubers?

  The answer is – to a certain extent, yes. Advances in the analysis of fossils now enable us not only to make interpretations based on the size and shape of bones, but to look closely at their chemical composition. As all the tissues of your body are, ultimately, built out of the molecules that you ingest, it’s possible to find clues about ancient diet entombed in those fossil bones.

  Specific chemical elements exist in subtly different forms, called isotopes. Some of these are stable, whereas others are unstable, radioactive versions. There are three naturally occurring forms of carbon. There’s the unstable, radioactive carbon-14, which is rare, but extremely useful to archaeologists as it’s used for radiocarbon dating. Most carbon in the world exists in the form of carbon-12, which has six neutrons and six protons in its nucleus. But there’s also a slightly heavier – and still stable – version, with an extra neutron, called carbon-13.

  When plants photosynthesise, they use sunlight energy to drive a reaction which captures carbon dioxide from the atmosphere, and eventually builds that carbon into brand-new sugar molecules. There are a few types of photosynthesis, each using slightly different chemical pathways. Trees and bushes tend to use a form of photosynthesis which includes the formation of a molecule with three carbon atoms as an early step. Ingeniously, plant scientists decided to call such plants ‘C3 plants’. Then there are plants like some grasses and sedges, which do photosynthesis slightly differently, creating a four-carbon molecule. You can see where this is going. They’re called ‘C4 plants’.

  Not only is the C4 pathway more efficient in its use of water molecules – making it a useful adaptation in more arid environments – it also means that the plant grabs more of the slightly heavier stable isotope of carbon-13. So C4 plants are relatively carbon-13-enriched. If an animal eats a lot of C4 plants – including, for instance, the roots and corms of sedges – the animal itself ends up being carbon-13-enriched too – even its bones.

  Anthropologists have used this difference between C3 and C4 plants to good ends. Chimpanzees’ diets are dominated by leafy C3 plants – their bones do not end up carbon-13-enriched. Our early hominin ancestors, some 4.5 million years ago, seemed to eat a similar, C3 plant-based diet. Between 4 and 1 million years ago, the climate was fluctuating, but the landscapes our ancestors inhabited were – on average – becoming drier and grassier. By about 3.5 million years ago, we know that our ancestors were eating a mix of C3 and C4 plants – and it might be that the C4 contribution came from starch-rich roots and tubers. Eating those hidden but ubiquitous foods could have helped ancient populations to expand and thrive in new habitats – including variable and unpredictable environments.

  Then, by 2.5 million years ago, there’s a split. Some hominins – which also happened to have very robust teeth and jaws – were eating mainly C4 plants (perhaps grass blades, seeds, sedge corms, depending on the season). At around the same time, other hominins, including the earliest members of our own genus, Homo, continued to consume a mixed C3–C4 diet.

  Although it’s often been argued that the advent of regular meateating provided the energy needed for our ancestors to evolve bigger brains, some researchers have recently suggested that plant foods – and in particular, starchy plant foods, like tubers – have been rather overlooked. Two key developments – one cultural, and one genetic – would have hugely helped to unlock the energy bound up in starch. That cultural development was cooking; the genetic one was the multiplication of a gene that produces an enzyme in sa
liva, to break down starch. We know that this gene multiplication happened some time after a million years ago. Salivary amylase works so much better on cooked than on raw starch, so it may be that the increase in the copies of this gene came hot on the heels of the adoption of cooking. There are archaeological suggestions of humans using fire as early as 1.6 million years ago, and definite evidence of hearths by 780,000 years ago. Together, cooking and plenty of salivary amylase may have provided the energy – in the form of ready-to-use glucose – for the enlarging human brain. And of course, a similar adaptation to eating starchy foods developed in dogs. Although dogs don’t produce salivary amylase, they do produce this starch-busting enzyme in their pancreas – and many of them have multiple copies of the pancreatic amylase gene.

  We know that our ancestors have been making and using stone tools for more than 3 million years. Those tools may have been used for processing both meat and plant foods. What’s really lacking in the archaeological record is any organic remains. So we have no idea when our ancestors started to use digging sticks. But as soon as they invented this simple tool, they would have had access to that buried treasure – that dependable resource which would become something of a staple, and a fallback food, for so many hunter-gatherers.

  What we can say with some certainty is that, by the time people were living at Monte Verde, their ancestors already had a long history of using digging sticks and eating roots and tubers. Eating wild potatoes was just the latest, local manifestation of that ancient type of behaviour.

  But when – and where – did potatoes become transformed from a gathered, wild food to a cultivated, domesticated species?

  The Cave of Three Windows and the unsolved riddle

  The Chilean wild potato, Solanum maglia, is a pretty plant with white flowers and small, purplish tubers, less than 4 centimetres in diameter, which likes to grow in damp ravines and around the edges of bogs, close to sea level, near the coast of central Chile. The species name comes from its name in the language of the indigenous Mapuche people of central Chile: malla. Darwin saw these plants in 1835, during his voyage on board the Beagle. He knew that the explorer Alexander Humboldt had written about these wild plants, and believed them to be ancestral to the domesticated potato. Darwin noted in his journal:

  The wild potato grows on these islands in great abundance, on the sandy, shelly soil near the sea-beach. The tallest plant was four feet in height. The tubers were generally small, but I found one, of an oval shape, two inches in diameter: they resembled in every respect, and had the same smell as English potatoes; but when boiled they shrunk much, and were watery and insipid, without any bitter taste. They are undoubtedly here indigenous …

  The domesticated potato, Solanum tuberosum, cultivated all over Chile and beyond, is very similar to its wild cousin. So similar, in fact, that even Darwin misidentified a Solanum tuberosum specimen he’d collected as Solanum maglia. But with the aid of microscopy, identification becomes much easier – it was the starch grains clinging to the inner side of the fragments of potato skin at Monte Verde that proved them to be the remains of wild Solanum maglia tubers.

  The archaeologists who dug Monte Verde wanted to taste the wild potatoes for themselves. They acquired a tuber, boiled it for half an hour, and ate it. It was a brave thing to do. Some researchers had suggested that wild potatoes would be too bitter to eat. They tend to contain relatively high levels of glycoalkaloids – such as solanine – which are part of the potato’s natural defence mechanism against infection and insects – and, it could be argued, against being eaten by humans. Glycoalkaloids impart a bitter taste to potatoes, and at high levels they’re toxic. It was thought that wild potatoes could contain such high levels of these compounds that they’d still be poisonous, even after cooking.

  But – like Darwin – the archaeologists not only survived the experiment, they didn’t detect any bitter taste to this mini-potato. Although some wild potatoes, further north in the central Andes, do produce bitter tubers, the wild Chilean potato seems to be perfectly pleasant to eat. And the archaeologists also reported that local inhabitants of central Chile happily eat wild potatoes today.

  But is Solanum maglia the ancestor of the domesticated potatoes we now eat? This is – or, at least, has been – a highly contentious question. As with many species, the question started out as that familiar one: was this a case of a single centre of domestication – or were there multiple origins?

  There are hundreds of types of potatoes, and botanists have argued about how to organise these into varieties and species. Some are between-species hybrids, making this task even harder. Classifications have resolved the different types into as many as 235 species, but the latest analysis – including genetic data – suggests that all potatoes can actually be grouped into 107 wild species and four cultivated species.

  Some of the most ancient varieties, or landraces, of potatoes are grown high up in the Andes – up to 3,500 metres above sea level – from western Venezuela to northern Argentina, and down in lowland south-central Chile. These landraces can be grouped into four species. One of these species, Solanum tuberosum, contains within it two clear, separate cultivars or subspecies – an Andean group and a Chilean group.

  In the early twentieth century, Russian botanists proposed that there had been two main centres of potato domestication – high up on the Peruvian and Bolivian plateau, near Lake Titicaca, and low down, in southern Chile. But then English botanists came up with a different model: a single origin of potatoes up in the Andes, and then an expansion of these domesticated potatoes southwards, to coastal Chile – adapting to the local conditions there. This seemed to match up well with the evidence – there were many more wild species from which Solanum tuberosum could have arisen, up in the Andes, compared with Chile.

  The earliest evidence of domesticated potato does come from the Andes – from a cave called Cueva Tres Ventanas (The Cave of Three Windows) in the Peruvian highlands, nearly 4,000 metres above sea level. The cave contains the oldest mummies in the world – dating to between 8,000 and 10,000 years ago, but the potato remains come from a younger layer, dating to around 6,000 years ago. And experiments have shown that Andean-type potatoes could be fairly easily transformed into something that looked like a Chilean type. For a while, then, it looked like a single origin of domesticated potatoes, high in the Andes, was the most likely scenario.

  But by the 1990s, another hypothesis had emerged – that the Chilean type developed as a hybrid of the Andean type with local, wild species in Chile. That wild species was suggested to be Solanum maglia – the same species of wild potato that was eaten at Monte Verde. But there’s such a enormous number of wild species, and potato genetics is hugely convoluted. And yet, finally, some form of clarity does seem to be emerging from the chaos. It seems that both the Russian and the English botanists were partially right. The latest archaeological and genetic evidence suggests that a wild potato species was first domesticated somewhere around Lake Titicaca, in the high Andes, between 8,000 and 4,000 years ago – around the same time that the llama was domesticated. But genetic studies also provide support for the hybrid origin of the Chilean potato cultivar, meaning that, as the original Andean domesticate spread, it hybridised with other, wild species. So, more than one wild species contributed to the gene pool of the first domesticates, and the simple question of origins (too simple for complex, interwoven, entangled biology) becomes more nuanced. Are we looking at multiple, independent centres of domestication, and separate lineages which are later brought together by interbreeding in some cultivars? Or are we looking at a single origin, in a discrete area, with a subsequent spread and interbreeding with other species? From a genetic point of view, it probably doesn’t matter so much. However it happened, genes from the lowlands and the highlands were brought together in the Chilean cultivar. But from a human perspective, this is a pertinent question, because it becomes about culture and innovation. Did the idea of growing potatoes emerge and take hold just once?
Did this idea gradually spread down into the foothills of the Andes and thence to the coastal plains of Chile? Or, once hunter-gatherers started eating potatoes, was it almost inevitable that some wild species would become domesticated, and that this then happened in at least two locations, possibly more? A single origin may be more likely, but it seems to me that we don’t quite have the tools or the evidence to answer that question yet. There’s still more work to be done before this particular mystery is solved.

  The potato goddess, the mountain and the ocean

  Wherever domestication first took off, it transformed the wild potato into something much more useful to humans. The most impressive difference between wild and domestic potatoes is in the size of the tubers and the length of the runners – the thin, horizontal stems that are sent out to sprout new plants. Wild potatoes have very long runners, which allow those new plants to propagate a good distance away from the parent; and they have small tubers. Domestication has trimmed the runners much shorter, and promoted larger tubers – both features which make the potato plant less fit in the wild, but much easier to harvest. It’s like the tough-rachis characteristic in wheat – an abject disadvantage for a wild plant, but a boon for one that’s teamed up with humans. Domesticated potatoes also contain much less of those glycoalkaloids that can make some wild potatoes so bitter, and even poisonous.

  Potatoes gradually became more and more important to Peruvian societies – and Andean civilisations rose. By the first millennium CE, potatoes had become embedded in society – they were a crucial, staple crop. The Inca Empire, which emerged in the twelfth century CE – stretching from Ecuador to Santiago – was fuelled by this subterranean commodity. The Inca even had a – slightly lumpy – potato goddess, called Axomama. And they grew so many varieties of potato that they needed to invent imaginative names to differentiate them – from the sinuous Katari Papa, the ‘snake potato’, to the difficult-to-peel Cachan huacachi, the ‘potato that makes the daughter-in-law weep’.