Tamed

by Alice Roberts

  In the modern control chamber, all the plants looked just like wild teosinte – with lots of branches, sprouting both tassels and female ears. The kernels of the ears ripened in a staggered fashion, rather than all at once. The late-Ice Age chamber was somewhat different. Most of the plants looked like teosinte, but some – about one in five – looked very much like maize. These plants developed a single stem, rather than lots of branches. Attached directly to the main stem were female flowers which developed into ears of corn where all the kernels ripened at the same time.

  It’s always been a bit of a mystery as to why teosinte seemed like an attractive candidate for cultivation to those early farmers. But if some teosinte plants – back at the end of the Ice Age – looked more like maize does today – with ears close to the stem and easy to harvest, and seeds ripening all at once – then perhaps it’s not so strange after all.

  Something even more intriguing happened when the researchers took seeds from just the maize-like plants grown under glacial conditions, and grew them in a climate matching that after the Ice Age, just into the Holocene, 10,000 years ago. Half of the plants from those seeds still looked like maize rather than teosinte. This means that early cultivators could have very quickly ended up with plants which mostly had that desirable, maize-like phenotype. We know that genetic changes also took place as maize became domesticated, but it seems that phenotypic plasticity is an important part of the story. The impressive plasticity of maize may represent an adaptation to variability – it suggests that its ancestors were exposed to fluctuating conditions and were more successful if they could adjust quickly to novel growing environments. We can no longer overlook this phenomenon – phenotypic plasticity – if we really want to understand how plants (and animals) became domesticated – and the important role that environment and ecology play today.

  And so, changing its form in response to climate and to selection by its human cultivators, maize began to spread from its homeland in the tropical forests of Mexico – up into the highlands, and into more northerly and more southerly latitudes – as the craze for agriculture took hold. The gradual spread of maize through the Americas allowed it to adapt to different environments – crucially becoming, not only a lowland plant, but a highland one; not only a tropical plant, but a temperate one.

  Phenotypic plasticity and new genetic mutations are two important sources of novelty, helping to produce the ‘extraordinary and conspicuous’ diversity of maize. But there was something else that seems to have contributed to its amazing ability to adapt to new environments – a little help from its wild relatives. As early maize spread from the lowlands to the highlands of Mexico, it hybridised with the mountainous subspecies of teosinte, Zea mays mexicana. Genetic studies have shown that up to around 20 per cent of the genome of highland maize comes from mexicana. Just like domesticated barley, picking up its drought resistance from wild strains growing in the Syrian Desert, maize was making the most of local, genetic ‘knowledge’ as it spread – by hybridising with its wild relatives.

  Maize appears to have migrated from Mexico via separate highland and lowland routes, into Guatemala, and on, further south. It had reached northern South America by 7,500 years ago. By 4,700 years ago, maize was growing in lowland Brazil, and by 4,000 years ago, it was in the Andes. From northern South America, maize spread northwards to Trinidad and Tobago, and the other islands of the Caribbean. The spread of maize to North America was much slower – beginning in the south-west corner just over 2,000 years ago, but then spreading right up to the north-east, into what is now Canada, in perhaps just a few centuries. And as maize spread, it kept changing.

  By the time of European contact with the Americas, a huge range of varieties of maize had developed, growing everywhere from Mexico to north-east America, from the coasts of the Caribbean and the valleys of Brazil, up into the heights of the Andes. In all its different forms, it was already a highly adapted and highly variable domesticate – primed and ready to spread rapidly across the globe – as soon as Columbus planted his foot on that beach.

  5

  POTATOES

  Solanum tuberosum

  The coarse boot nestled on the lug, the shaft

  Against the inside knee was levered firmly.

  He rooted out tall tops, buried the bright edge deep

  To scatter new potatoes that we picked,

  Loving their cool hardness in our hands.

  Seamus Heaney, ‘Digging’

  Ancient potatoes

  A fragment of grey, crumpled, thin, leathery material – so small it would almost fit on a fingertip. Quite uninspiring. If you found it in your back garden, you’d think it was merely recent detritus. Something that had escaped from the compost heap, perhaps. (Something as unremarkable as a bit of chipped stone pushed out from the burrow of a lobster.) And yet, this is a very precious piece of archaeological evidence.

  This little black piece of organic stuff came from an archaeological site that was excavated during the 1980s in southern Chile, called Monte Verde. It’s one of the oldest, securely dated sites of human habitation in the Americas, North or South, at around 14,600 years old. It’s almost contemporary with the Natufian sites in the Levant, but the big difference is that modern humans had lived in the Near East for tens of thousands of years before this. At Monte Verde, they were still relative newcomers.

  I visited Monte Verde in 2008 – with geologist Mario Piño, who had dug at the site. We arrived at this incredibly important place to find a field, with a few sheep grazing on the mossy banks of the fast-flowing Chinchihuapi Creek. We were so far from England, but I could have been hiking in the Lake District – it was such a familiar rural idyll. And without Mario’s expert help, I would have had immense difficulty locating the precise location of the site – the archaeology had all been covered over, and had completely merged back into the landscape. In fact, I probably wouldn’t even have known it was there.

  ‘The site, like so many others, was discovered by chance,’ Mario told me. ‘Local villagers were widening the creek. When they were removing the sediment, cutting the curves, they found huge bones, and kept them. Two university students who were travelling round the place took the bones to Valdivia.’

  It was lucky they did. The huge bones turned out to be from Ice Age animals – that went extinct around 11,000 years ago. The find prompted scientists from Valdivia University to investigate further. What seemed at first to be a purely palaeontological site, containing the remains of Pleistocene animals, became even more interesting when the researchers began to find stone tools and other relics. People had clearly been here too – a very long time ago.

  The wet, peaty soil at the site meant that organic material was extremely well preserved. Things that would have quickly rotted away at most sites had survived here, trapped in a time capsule. The archaeologists began to find the remains of wooden stakes, stuck into the ground, and it soon became clear that these were outlining the frame of a building – some kind of hut. And it was big – about 20 metres long. In the soil around the stakes there were dark fragments of tough organic material: the animal hide that had been used to cover the long cabin. The archaeologists also found evidence of fire pits or hearths – full of charcoal – both inside and outside the building. The preservation was astonishing. There was even a child’s footprint, perfectly preserved in the mud. About 30 metres away, they uncovered evidence of a smaller hut, full of animal and plant remains, including butchered mastodon bones and chewed-up and spat-out lumps of seaweed.

  The site appears to have been abandoned and then fairly rapidly buried – it seems likely that the area had become very boggy and, after the humans left, reedbeds quickly took over. The peat built up, sealing the archaeology and preserving all those precious organic remains – forgotten, until the villagers decided to widen the creek.

  The preservation of organic matter at the site gave the archaeologists an unprecedented opportunity to look at the whole range of animals and plants tha
t formed the diet of the hunter-gatherers who lived there. The Monte Verdians had eaten the meat of now-extinct animals – including elephant-like gomphotheres and ancient llamas – and a huge variety of plants: forty-six different species in all. The plants included four species of edible seaweed – some present as those chewed-up cuds – which may also have been used for medicinal purposes. And amongst the plant remains were those tiny, unprepossessing, leathery scraps – the crumpled remnants of the skins of ancient, wild potatoes: Solanum maglia. Nine fragments were found in all, from small hearths or food pits inside the huts. Analysis of starch grains still sticking to their inner surfaces confirmed the species. These are still the earliest remains of potatoes ever discovered, in association with humans – our ancestors had already developed a taste for the humble spud some 14,600 years ago. Wooden digging sticks, perfect for unearthing those potatoes, were also found at the site.

  ‘We found food from all four seasons,’ said Mario. So it seemed that this place was more than just a seasonal camp – it had been used all year round. This is intriguing too, as we tend to assume that people at this time were all quite nomadic, making temporary camps, striking them and moving on. The slightly later, Mesolithic site of Star Carr challenged this assumption back in England. Monte Verde presents us with the same reality check in South America. We shouldn’t look for a one-size-fits-all for any period in the past – or indeed, the present – and we shouldn’t underestimate just how sophisticated our ancestors were. In some places, it would have made sense to stay mobile. In others, the conditions and resources of a particular region meant that settling down in one place was a perfectly viable way of life. Human behaviour changes to suit local ecology.

  The site of Monte Verde has sparked some controversy, due to its early date. During the twentieth century, a prevailing hypothesis held that the earliest inhabitants of the Americas arrived, in the north, around 13,000 years ago, carrying with them a particular stone toolkit known as ‘Clovis’, after the site in New Mexico where characteristic stone points were discovered in the 1930s. Monte Verde is clearly too early to fit with that model.

  By 1997, lead archaeologist Tom Dillehay was so fed up with the criticisms – that the dating of Monte Verde couldn’t possibly be right – that he invited a group of eminent colleagues to visit the site, to see the artefacts for themselves and make up their own minds about it. They all agreed that the site was indeed archaeological, and that there was no reason to doubt the pre-Clovis radiocarbon dates.

  Monte Verde is now just one of several ‘pre-Clovis’ sites providing solid evidence of people inhabiting the Americas much earlier than the ‘Clovis-first’ hypothesis would allow. The consensus view is still that the first colonisers arrived in the north, moving across the Bering land bridge from north-east Asia. There are a couple of very early sites in northern Yukon, indicating human presence at those high latitudes, which date to before the peak of the last Ice Age, 20,000 years ago. But a massive ice sheet effectively sealed off most of North America. Colonisation of the rest of the continent, and then South America, had to wait until the ice began to melt. Pre-Clovis sites in North and South America show that the colonisation must have happened fairly soon after the last glacial maximum, perhaps around 17,000 years ago. Although much of North America was still under a massive ice sheet at this time, environmental analyses have shown that the northern Pacific coast would have thawed out enough for people to have taken this route into the Americas. Then they spread southwards, giving them just about enough time to have reached Chile, by 14,600 years ago.

  Just how long was it until the early hunter-gatherers in South America discovered those little parcels of deliciousness hiding in the soil? My guess is: not long at all.

  Digging for tubers might seem like an extraordinarily inventive way of obtaining food. Picking fruits and nuts off trees, even collecting seaweed off rocks on the beach – those all seem like fairly obvious approaches to foraging. On the other hand, sharpening yourself a digging stick and going poking around for hidden, underground morsels: this seems on the face of it to be either deeply strange or desperate behaviour – or alternatively, a stroke of genius.

  But our ancestors have been carrying on in this way for not only thousands but, potentially, millions of years.

  Buried treasure

  Our closest living animal relatives are chimpanzees and gorillas. Both of these forest-living apes prefer eating ripe fruit – but when this food is scarce, they fall back on leaves and the pithy insides of stems. It seems likely that, around 6–7 million years ago, the common ancestor of humans and chimpanzees would have relied on a similar diet. But then the ancestors of humans and chimpanzees diverged. The apes that belong to our own branch of the family tree of life on the planet are known as hominins – characterised by habitually walking around on two legs, and possessing increasingly large brains compared with their forebears. We’re the only living representatives of a once bushy hominin sprig on the tree of life. We now know of around twenty hominin species – all of them extinct, except us. When early hominins start to appear in the fossil record, they not only show skeletal adaptations to walking on two legs, their teeth have changed too – they have larger molars with much thicker enamel than their predecessors. In other primates, tooth shape and size seems to relate less to the preferred, everyday diet and more to the types of foods that animals resort to when times are hard. This suggests that the change to hominin teeth may also reflect a change in fallback foods. This was a time when the great, dense forests of Africa were starting to break up. The landscape was becoming more diverse – and it seems that our ancestors were beginning to exploit these more open environments.

  There are some obvious differences between savannah and forest ecosystems, but underground there’s an important, hidden contrast. Savannahs contain many more plants with ‘underground storage organs’ – such as rhizomes, corms, bulbs and tubers. Comparing a modern savannah in northern Tanzania with the rainforest of the Central African Republic, ecologists have found an enormous difference in the density of tubers and other underground storage organs: 40,000 kilograms in every square kilometre of the savannah, compared with a meagre 100 kilograms per square kilometre in the forest. Were our ancestors tapping into this particular rich resource, under the expanding grasslands of Africa? The prize for digging out these tubers, and the like, was a parcel of energy – but a tough one. It may not have been the food of choice, but it could make a big difference in desperate times. Those larger, well-armoured teeth of our early ancestors could represent an adaptation to this new fallback food.

  Contemporary foragers make good use of roots, tubers and bulbs. I’ve been fortunate enough to have seen for myself how one group of modern hunter-gatherers – the Hadza – take advantage of this particular type of food. In 2010, I went on an expedition to meet a Hadza group in a remote part of Tanzania – with anthropologist Alyssa Crittenden.

  Flying in to Kilimanjaro Airport, I then set off in a four-by-four. The first half of the journey – about three hours – was easy enough, on tarmac roads, passing through small villages. But then we suddenly took a left turn on to a dirt track, and for most of the next three hours I was being thrown around in the Land Cruiser as the driver, Petro, drove capably along rutted tracks, down into sandy stream beds and up steep banks, until we reached the edge of Lake Eyasi – a vast salt flat with little sign of any water. We dropped down into the lake – and got stuck on the rim, at an awkward angle. There was nothing we could do – this vehicle was well and truly immobilised.

  It was late and dusk was falling fast. We didn’t fancy spending the night in the Land Cruiser, so we called through to the advance party of the team, who had already arrived and set up camp. They came to rescue us in another Land Cruiser – winching out our vehicle.

  We weren’t far from the camp, and when we arrived there I met Alyssa, the anthropologist who had been studying and living with an indigenous, hunter-gatherer group for years. Our tented safari c
amp had been pitched near the Hadza camp, under the trees. I thought everyone might have already gone to bed, but Alyssa said that the Hadza were excited about meeting me. So in the gathering darkness, I went with Alyssa and was introduced to a group of around twenty people, shaking hands and saying ‘Mtana’. The women wore dresses and kangas of bright, printed material, and a few had beaded headbands. Some of the men were wearing T-shirts and shorts, others wore loincloths, and necklaces of black, red and white beads. Everyone’s hair was cut very short. I gave out the small gifts that Alyssa had asked me to bring: little bags of beads for the women and steel nails for the men, which would be hammered into arrowheads. These people met me with such warmth and openness – as a friend of a friend.

  In the few days I spent with the Hadza, I felt as though I learnt a huge amount about their way of life – although it was really just a glimpse. I was extremely lucky to have Alyssa there as my guide; her depth of knowledge was extraordinary. I watched Hadzabe men and boys mending their bows and arrows and then setting off on a hunt. I also observed – from a safe distance – a man braving the stings of angry bees to collect honey from a hive hanging in a tree. On return to the camp, he was mobbed by women and children, all wanting a piece of the honeycomb. I talked to the Hadzabe women – through two layers of translation – about having children and childcare. And I accompanied the women when they left camp to go on foraging expeditions into the bush. They had a specific target in mind – and that was tubers.