Friday, July 5, 2024

How ghost cities in the Amazon are rewriting the story of civilisation

folks are waking up to terra preta agriculture.  I woke up when i began this blog in 2007 and that was because i researched natural zeolites in 1990 or so and discovered that carbon was a zeolite.

The direct take home is that adding biochar to spent tropical soils make them fully productive forever as the nutrient will not escape.

Agriculture then in the tropics becomes maintaining an active food forest and garden sufficient to feed your family.

Populations of millions result as is proven here.

How ghost cities in the Amazon are rewriting the story of civilisation

Remote sensing, including lidar, reveals that the Amazon was once home to millions of people. The emerging picture of how they lived challenges ideas of human cultural evolution

2 July 2024

Try to imagine an environment largely untouched by humans and the Amazon rainforest might spring to mind. After all, large swathes of this South American landscape are blanketed in thick vegetation, suggesting it is one corner of the world that humans never managed to tame. Here, there must have been no deforestation, no agricultural revolution and no cities. It seems like a pristine environment.

Or so we thought. But a very different picture is emerging. Archaeologists working with Indigenous communities have been shown crumbling urban remains and remote sensing technologies such as lidar are revealing the footprints of vast ghost cities. With so much evidence of ancient human activity, it is now thought the pre-Columbian Amazon was inhabited by millions of people – some living in large built-up areas complete with road networks, temples and pyramids.

But that’s not all this research reveals. Paradoxically, it also provides evidence that the traditional view of the Amazon isn’t completely wide of the mark. For instance, while the ancient Amazonians managed their landscape intensively, they didn’t deforest it. And although they developed complex societies, they never went through a wholesale agricultural revolution. This might suggest that the pre-Columbian Amazonians broke the mould of human cultural development, which is traditionally seen as a relentless march from hunting and gathering to farming to urban complexity. The truth is more surprising. In fact, we are now coming to understand that there was no such mould – civilisation arose in myriad ways. What looks like an anomaly in the Amazon is actually a shining example of a process that was as vibrant and diverse as the rainforest itself.

Despite its obvious biodiversity, the Amazon rainforest is rooted in impoverished soil. This realisation led to the long-held belief that it couldn’t sustain large numbers of people. The first hint that this assumption might be wrong came in the 1960s, with the suggestion that mysterious patches of fertile soil, known as terra preta, were created by past societies to boost crop growth. The scale of these societies began to emerge three decades later, when Michael Heckenberger at the University of Florida in Gainesville began working with the Kuikuro, an Indigenous group who live in Brazil’s Upper Xingu region. “After two weeks, the Kuikuro chief, Afukaka, took me to a site that was 20 times as big as the contemporary village,” says Heckenberger. “Then he took me to another.” Clearly, Afukaka’s forebears had built on a grand scale. How was this possible?

The discovery of terra preta sheds light on the Amazon’s earliest inhabitants

Associação Indigena Kuikuro do Alto Xingu

Discoveries made this century have finally allowed us to answer that question. The story begins when humans first arrived in the Amazon. Exactly when that happened is up for debate – estimates vary from 27,000 to 13,000 years ago – but it seems to have been remarkably soon after people arrived in the Americas. Those early Amazonians didn’t immediately start building large settlements deep within the rainforest. Instead, they stuck to the margins of the Amazon basin where an astonishing variety of landscapes still exists. “There are lush evergreen forests, seasonally flooded savannahs, huge areas of wetlands – it’s very diverse,” says José Iriarte at the University of Exeter, UK. “Right from the start, these hunter-gatherers were looking for transitional zones where they could exploit different environments.”

Evidence of this earliest stage of Amazonian life is preserved at several rock shelters in an area of Colombia called the Serranía de la Lindosa. The shelters, which Iriarte and his colleagues have been excavating since 2015, show signs of human habitation stretching back at least 12,600 years. At this time, the Amazon was a few degrees cooler than it is today. But arguably the biggest difference was the presence of large mammals, including giant sloths, elephant-like gomphotheres and huge ungulates. Spectacular rock art in the Serranía de la Lindosa depicts some of these animals, suggesting these megafauna were an important component of the early Amazonians’ diet, says Iriarte. What’s more, the megafauna had co-evolved with flora that produced fruit large enough to satisfy the hunger of enormous herbivores, thereby encouraging them to disperse the seeds. This fruit – including avocado, cacao and various forms of squash – quickly found a place on the hunter-gatherer’s menu too, meaning early Amazonians enjoyed a varied diet.

By 11,600 years ago, most of the megafauna had disappeared, driven to extinction through a combination of human activity and climate change. Then came a new way to obtain food. Instead of simply foraging, some Amazonians began domesticating plants. José Capriles at Pennsylvania State University, Iriarte and their colleagues published the first evidence of this early cultivation in 2020. It comes from the flooded savannahs of the Llanos de Mojos in the Bolivian Amazon. Here, the modern grassy landscape is littered with curious little hills, many about a hectare in size, and each covered in thick vegetation. “We’ve mapped over 6000 of them,” says Capriles.

It turns out these “forest islands” are human-made mounds, some dating back 10,800 years. They sustain forests today because centuries of human activity left their soils more fertile than the surrounding grassland. Capriles suspects they began as temporary camps, but as the soils became enriched by human waste, some of the plants that the foragers ate, including squash and manioc (also known as cassava), began growing there. Then, people started cultivating and ultimately domesticating them.

Rock art found in Colombia indicates that the early inhabitants of the Amazon hunted megafauna

Jose Iriarte/Last Journey

Domestication evidently caught on. Soon, as well as growing these short-lived crops in small gardens, the Amazonians were planting groves of long-lived trees, including peach palms and Brazil nuts. In fact, as the scope of these endeavours has become clearer, researchers have begun to recognise the south-west Amazon as an independent centre of plant domestication – one of only five in the world.
Gardeners not farmers

At this point, it seems we are on a familiar trajectory. With the traditional model of human cultural evolution as a guide, we might assume the Amazonians would recognise the advantages of growing their own food and become full-time farmers living in permanent settlements. Their populations would then grow and expand across the entire Amazon, and their culture – from farming to languages – would spread far and wide. That isn’t what happened.

There is so little evidence of intensive farming in the pre-Columbian Amazon that recent studies conclude there never was a farming revolution in the region like the one that swept across Europe from around 10,000 years ago. There is some evidence for cultural spread – languages in the Arawakan family, for instance, are spoken in many parts of the Amazon – but this diffusion was never particularly strong. The lack of a sweeping wave of farmers might help explain why the Amazon of today retains a mind-boggling diversity of languages – more than 300, including about 50 that are unrelated to any known language, according to Jonas Gregorio de Souza at Pompeu Fabra University, Spain, who has explored the spread of Amazonian languages.

Why did farming fail to take hold? Environmental factors might have played their part – not least, those impoverished Amazonian soils. “They are naturally nutrient poor,” says Crystal McMichael at the University of Amsterdam. “It’s really hard to grow a big sedentary agricultural society unless you have some type of soil modification.”

Amazonian societies did eventually begin modifying the soil and improving its fertility, creating the patches of terra preta that researchers have known about for decades. But this didn’t happen on a large scale until about 2500 years ago. Research by McMichael and Mark Bush at the Florida Institute of Technology suggests it was only then that human populations began to grow exponentially and people spread freely across the region.

Perhaps more importantly, early Amazonians may not have seen farming as a worthwhile pursuit. They still had access to rivers teeming with fish, and their cultivated gardens and orchards provided plenty of fruit and vegetables. Abandoning this smorgasbord to focus on farming just one or two cereal crops such as maize, which arrived in the Amazon some 7000 years ago, may have had little appeal. This ambivalent attitude might seem surprising given that cultivation of crops has long been seen as a step that leads rapidly and inexorably to full-time farming. But recent archaeological findings have changed this thinking. Even in places where cultivation resulted in intensive farming, including North America and East Asia, it often did so only after a significant lag, sometimes lasting millennia.

We now also know that the adoption of farming wasn’t a prerequisite for further social developments: many complex hunter-gatherer societies have existed throughout human history. Instead, societies tend to become more politically, technologically and economically complex by intensifying production of key foodstuffs, because doing so “almost inevitably” encourages the establishment of an elite that can control access to the resource, says Adrian Jaeggi at the University of Zurich in Switzerland.
Elites and hierarchies

This, rather than a lack of farming, could have created a barrier to the complexification of pre-Columbian Amazonian societies, relying as they did on a wide range of foods distributed across the landscape. Moreover, controlling access to such resources would have been virtually impossible, limiting the opportunity for Amazonian elites to emerge.

At first glance, this seems to fit with the evidence. For instance, beginning about 1000 years ago, the TapajÓ people established themselves in the central Amazon, where they built a network of settlements based around two large villages, Aldeia and Porto. Generally, such settlements would serve as seats of power for a ruling elite. Not here. Archaeological excavations in the past 20 years have failed to reveal evidence of a concentration of prestigious goods, says Denise Gomes at the Federal University of Rio de Janeiro, Brazil. Instead, objects of similar social value are found in all TapajÓ settlements, both large and small, suggesting smaller communities retained their autonomy, says Gomes. If the TapajÓ are representative of other Amazonian societies, that would explain why the pre-Columbian Amazon is sometimes described as a region in which states or other forms of permanent hierarchical structures failed to emerge.

However, the story turns out to be more complicated. “The groups we see today in the Xingu [region] and elsewhere are very hierarchical despite living in communities of no more than 100 people,” says Heckenberger. “And it’s because their heritage descended from large, structured and highly organised societies.” Support for this assertion doesn’t just come from the ancient settlements he was shown by Afukaka. In recent years, remote scanning has revealed similarly large settlements across the Amazon, all built in the past 2500 years after the human population expanded. There is also evidence that some of these settlements were linked by extensive road networks. These were sometimes built on a grid system reminiscent of Manhattan, with straight roads up to 10 metres wide. The scans have found signs of engineering work too, including terraced fields, drainage canals and weirs for trapping fish.

Then there are the monuments. In Bolivia’s Llanos de Mojos, these spectacular structures, all made from earth, include stepped platforms and 22-metre-tall pyramids built starting around 1500 years ago. They dwarf the forest islands built by the early Amazonians 10,000 years ago. “Some people would like to think a political system lacking hierarchy can still build such monumental architecture – but I’m sceptical,” says Capriles.

Remote sensing using lidar reveals ancient structures (right) in Ecuador’s Upano valley

Stephen Rostain

Complex societies

The complexity of ancient Amazonian societies is also evident in the way they managed the resources available to them. “We’re looking at societies that had no stone and no bricks,” says Heckenberger. “Everything is organic, and so the industrial demand for wood and grass was tremendous. Not just for house construction, but for portable artefacts – every hammock, every tool.” This economic reliance on the rainforest encouraged the ancient inhabitants of the Xingu to develop an intricate landscape management strategy called “garden urbanism”, which isn’t unique to the Amazon – evidence of similar ways of life is found in other places where civilisations have taken root in tropical forests, including in parts of Africa and Indonesia.

We still don’t really know how some pre-Columbian Amazonian societies achieved complexity. One suggestion is that they did it by focusing on, and then intensifying production of, aquatic resources that could be controlled by an emergent elite. Another idea, favoured by Heckenberger, sees hierarchies forming by accumulating political capital. In other words, the authority needed by elites to command the construction of monuments and other engineering projects was rooted in symbolism rather than the accumulation of food surpluses or prestigious goods. Whatever the explanation, the fact that complex societies did emerge confirms a growing realisation that human cultural development – from hunter-gatherer to urban dweller – came in a wider variety of forms than we had assumed. Far from being an anomaly, pre-Columbian Amazon civilisations are a perfect illustration of that paradigm shift. “The more we learn, the less I believe in Amazonian exceptionalism,” says Heckenberger.

The Upano valley in Ecuador

Stephen Rostain

The Amazon continued to be home to large numbers of people for thousands of years. By the time Europeans arrived in the 16th century, populations in the region had dropped somewhat – perhaps due to disease, says Heckenberger. Nevertheless, the explorers still reported encountering large societies, some so well organised that social elites could assemble an army of 60,000 warriors if the need arose. Such reports were easy to dismiss, however – particularly as Amazonian populations dwindled and fragmented as a result of the expansion of European colonists and the diseases they brought with them – and the idea of the rainforest as a vast natural wilderness took hold.

Now the tide has turned, but Amazonian archaeology is still in its infancy. Undoubtedly, there are many treasures yet to be discovered. With new technology and so much ground to survey, the picture is changing fast. Just last year, remote scans suggested that there are more than 10,000 ancient earthworks still hidden in the Amazon. We can only guess at the secrets they have to reveal. “Anything at this point is conceivable,” says Capriles.

Colin Barras is a freelance writer based in Ann Arbor, Michigan

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