In this lecture we explore one of the most important revolutions in the history of humanity and even of our planet, the transition from foraging to farming. Let me pose three questions to you that anthropologists and archaeologists have frankly struggled to answer for more than a century. Why would humans give up foraging, a lifeway that had successfully sustained them for almost 200,000 years, and adopt agriculture?
Did this happen all over the world at the same time? Or did some humans in just a few places adopt farming and many others not? And what has the impact of the agricultural revolution been on human lifeways?
and on the biosphere. We have seen that around 12,000 years ago, humans were living on all Earth's continents except Antarctica. Wherever they lived, humans survived through foraging, by using collective learning to invent a range of technologies perfectly adapted to different environments, from the icy world of the Arctic to the deserts of Australia.
So collective learning and technological innovation were clearly going on, but the small size of human communities were not. in the old Stone Age, and the limited exchanges between them meant that the pace of change had been slow for close to 200 millennia. But then something changed, and it changed quite quickly. By 11,500 years ago, new subsistence technologies were beginning to appear in certain regions of the planet, technologies that, by enabling humans to cultivate their own sources of food, over time gave humans access to More energy and more resources.
This meant that not only did human populations begin to increase globally, but in the new agricultural zones, humans were living in larger and denser concentrations in new types of communities, such as villages and towns. Increased densities like this were frankly impossible during the Paleolithic because foragers needed a huge range of territory to support themselves, roughly two square kilometres per person. But farming can support many more people in the same area.
One example, in Bangladesh today, agriculture can sustain a population density of almost a thousand people per square kilometre. Where agriculture was adopted, denser populations appeared and the pace of historical change began to speed up, putting humans onto a new historical pathway that led directly towards the astonishing world of complex states and civilisations. But where foraging remained the dominant life way and populations remained small and scattered, change was generally slower. So this meant that for the first time in human history, the pace of change began to vary from region to region.
The transition to agriculture was thus of such profound significance that it clearly marks the crossing of another threshold of complexity by our species and indeed by planet Earth. The timing of the transition was critical. Agriculture was adopted early in parts of Afro-Eurasia, much later in the Americas and the Pacific, and hardly at all in most of Australasia. And this had significant implications for the appearance of civilizations, as we shall see. To understand why and where agriculture appeared when it did, let's consider how foraging and farming differ.
We've learned that foragers are very good at finding new sources of energy by spreading into new environmental niches. a process that we termed extensification. In contrast, farmers largely stay in one place, so they have to find ways to extract more energy from the area of land that they have available, a process we call intensification.
Foragers live off a wide variety of animal and plant species that are products of natural selection. Farmers, on the other hand, depend upon a much smaller number of species and have learned to increase their output through artificial selection. Successful farming also depends on the establishment of a strong relationship between plants, animals and the human farmer, an interaction that evolves into a form of symbiosis, a biology term to describe species codependence. Symbiosis is common in the natural world, where different species have evolved to rely on each other for food or for protection, often becoming so dependent that they can no longer survive alone. One example, along the Australian Great Barrier Reef.
the small, cleaner wrasse fish survives by cleaning the gills and the teeth of other fish, some of which would probably eat the small fish if it was not performing such a useful task. The wrasse lives off the food it picks out of the mouths of other fish, while the latter depend upon the dentist to keep their teeth and gills clean. Another example of a symbiotic relationship is that between honeypot ants and aphids, which are tiny insects that feed on the sap of plants. The ants domesticate the aphids by herding and milking them to obtain the honeydew they produce. But at the same time, they protect the aphids from predators and help them reproduce.
Doesn't this sound very similar to farming? Like honeypot ants, humans have learned over the course of 11,000 years to herd and manipulate useful species like corn and cattle, and how to increase production of our domesticates to support more of our own species. Now, humans obviously benefit from this symbiotic relationship, but so too do our domesticated species, which we protect from predators and help reproduce, ensuring their success as a species.
Note, though, that the impact of this relationship has been different for each partner. Humans have changed. culturally because of domestication, leading to the invention of new technologies and new life ways and the evolution of our communities from small foraging bands to complex interdependent cities, states and civilizations.
Our domesticates have changed genetically, often evolving into an entirely new species. Let me give you two quick examples. Teosinte, the ancestor of modern corn, is in its natural state a small, weedy... and not very nutritious plant, although it can survive in the wild without human assistance.
Over thousands of generations, American farmers turned teosinte into varieties of modern corn, a plant that is much larger and more nutritious, but that can no longer reproduce without human intervention. The domestic sheep is another example. The ancestor of all domestic sheep was the mufon, which still survives in wild populations today in Turkey, Iran, Sardinia and Corsica. The domestic sheep is a lot less intelligent, more docile and virtually helpless compared to the mouflon.
But because humans have protected it and encouraged its reproduction, the modern sheep is biologically much more numerous than its wild ancestors. In fact, current estimates are that the planet supports a global population of over 1 billion sheep today. Okay, let's get back to the key questions of where, when and why the transition to agriculture occurred. It appeared that this was not an abrupt change.
The road from gathering plants in the wild, then cultivating and finally domesticating them, was long and convoluted. Geneticists working on plant genomes have been crucial in unlocking the nuances of this transition as they look for genetic evidence of physical changes in species as a product of domestication. Plant genomes show us that humans who are harvesting and eating wild cereals for thousands of years before actual domestication began.
A good example of this comes from the archaeological site of Ohalo II on the southwest shore of the Sea of Galilee in Israel, which was first settled 25,000 years ago, probably by Natufians, more than 10,000 years before farming began. Archaeologists have found evidence of up to 90,000 individual plants that were eaten by the inhabitants. But there is no genetic evidence of any attempt at domestication, even though the remains of wheat and barley on stone implements indicate that the residents were grinding wild grains to make flour and probably baking dough in hearths. The earliest sites and dates for actual species domestication are difficult to determine, but there is little doubt that the first successful attempt at domesticating a species was undertaken by Paleolithic foragers, and that was the domestication of the dog. The oldest actual remains of a domesticated dog have been dated to around 15,000 years ago.
This date comes from the 2002 discovery of two dog skulls found close beside a mammoth bone hut in the upper Paleolithic site of Alisevichy 1 in central Russia. In 2013, these skulls were positively identified by DNA sequencing as belonging to the Canis lupus familiaris, or dog family. In 2015, researchers did an analysis of the complete mitogenome sequences of 555 individual modern and ancient dogs.
This research indicated that a significant increase in the size of the population had occurred around 23,500 before present, leading them to conclude that this might mark the actual date of dog domestication, the first successful domestication of any species by humans. As Oxford paleoarchaeologist Gregor Larson once famously put it, The dog was the first domesticate. Without dogs, you don't have any other domestication. You don't have civilization. The domestication of other species by early farmers occurred gradually around the world over long time periods.
This began in Southwest Asia around 11,500 years ago, then in Northeast Africa, perhaps 1,000 years later, in East Asia at least 9,000 years ago, and eventually in New Guinea. in sub-Saharan Africa, in South Asia, and the Americas in the millennia that followed. So what prompted the transition? Now, the obvious answer might be that, as with the wheel, some creative individual simply invented farming, and it worked so well that everyone else just copied it. But one problem with this theory is that agriculture appeared separately in different regions of the world that had no contact with each other.
This isolation is most probably true of China and New Guinea, and certainly is the case in the Americas, a world zone that was geographically isolated from Afro-Eurasia, but where very similar processes of domestication occurred. We also know that agriculture was not necessarily seen as a more attractive life way to foraging, as a better idea, because foraging persisted for millennia in close proximity to early farming communities, particularly in northern Australia. Agriculture was more physically demanding than foraging, also more stressful. Farming was also less healthy than foraging, partly because farmers narrowed the range of their food choices and thus their nutritional intake, and also because the repetitive physical motions required of farmers were not as good for the body as the more generalized physical activity of hunting and gathering.
Skeletal remains also show that early farmers were not only subject to greater levels of stress, but also to new diseases, many of which spread from domesticated animals to humans, a problem we still face today. The adoption of farming actually shortened human lifespans and increased infant mortality rates amongst early farming communities. So the brilliant idea theory, the appearance of some Paleolithic farming Einstein to explain the emergence of agriculture, simply will not work. An alternative approach more widely accepted today is to explain the agricultural revolution as a step-by-step process in which conscious human decision-making may have played only a limited role.
Critical to the evolutionary, not revolutionary model is climate change and the emergence of environmental conditions that facilitated the transition, coupled with demographic pressure as a result of increasing population densities in some regions. Now, the last cycle of the most recent ice age began around 110,000 years ago, and global temperatures plunged to their coldest level between 21,000 and 17,000 years ago. Conditions were so cold that forests disappeared and frigid tundra covered much of the planet.
Spain, 17,000 years ago, would have looked more like Siberia today. Under these conditions, foraging was the only survival strategy possible for humans. And this remained the situation until the beginning of the Holocene Epoch around 11,700 years ago, when the Earth experienced a rapid global warming at the end of the last ice age.
The Holocene was not only warmer and wetter, but also more climatically stable. And as different groups experimented with domestication, they increased in size relative to foraging bands. Researcher Peter Richardson argues that This increase in group size led to intergroup competition, and this more or less forced communities to adopt farming. Now, building on the work of Richardson and many other specialists, Big History offers a five-step model to try and explain the origins of agriculture.
The first step is actually a precondition. Humans already had a lot of the necessary knowledge and skills for farming. Remember, for almost 200,000 years, humans had been farming.
endlessly manipulating other species and landscapes to enhance our food supply and to reduce our exposure to predators. So our foraging ancestors were already pre-adapted culturally to manipulate the natural environment. They had an immense amount of knowledge about plants and animals and how to protect useful species through not over-exploiting them.
And foragers had also demonstrated their ability to radically transform their environments through practices like firestick farming. and the hunting strategies that led to megafaunal extinctions. Step two is another precondition, really. Some animal and plant species were also essentially pre-adapted as potential domesticates.
Now by this I mean that some animals and plants had evolved in a way that made them more suitable for domestication than others. Obviously not all animals and plants are equal when it comes to potential domestication. For example, of the 150 or so species of land mammals on the planet, farmers have been able to domesticate only 14 such species. This is because potential animal domesticates have to meet some pretty demanding criteria, including rapid growth, regular birth rates, a herd mentality and a good disposition.
Of the 200,000 higher plants growing on earth, only about 100 have proven to be reliable domesticates. It was the domestication in West Asia of three cereals, emma and einkorn wheat and barley, that effectively marked the beginning of the transition from foraging to farming. Emma wheat in particular has significant genetic advantages.
It can adapt to very diverse environments. It gives good yields from poor soils. It has the ability to rapidly genetically diversify, and its resistance to certain fungal diseases like stem rust is also important.
All of these advantages, coupled with the fact that Emma has a reputation for baking good bread, explain its global success as a domesticate. Geneticists have identified several locations in southeastern Turkey as the most probable places of origin of wild emmer wheat. But the earliest evidence of domesticated emmer actually comes from a site near Damascus in Syria.
So it was perhaps from the Damascus Valley or some other adjacent fertile crescent early farming site that domesticated wheat spread initially across Afro-Eurasia and eventually all around the world. In 2012, farmers produced 960 million metric tonnes of wheat globally. providing something like 20% of all the calories consumed by the more than 7 billion humans alive that year. Modern versions of weeds such as durum and common have today almost completely eclipsed the ancient unkorn and emigraines, which today are grown only in a handful of mountainous regions in Eurasia. There were many such promising potential domesticate species 11,000 years ago in Southwest Asia.
The region had just the right climate, fertility and soils, as well as a wide suite of wild animal species growing and grazing in the highlands of the Fertile Crescent. The abundant potential of the Fertile Crescent is one obvious reason why agriculture began there. Whereas the weedy and generally unnutritious nature of Teosinte, the ancestor to modern corn, might be a reason for the much later appearance of agriculture in the Americas. Teosinte does not have large ears of grain like emma and einkorn wheat, offering little nutritional return for the early American farmer. Instead, teosinte had small nut-like kernels distributed in small feathery knobs over the numerous tertiary branches.
Plant geneticists have been able to identify the specific genes that had to be modified by artificial selection to enable teosinte to make the transition to modern corn. But it took early Native American farmers many, many generations of selective breeding of Teosinte for these genetic changes to manifest themselves, delaying the widespread availability of a nutritious and successful grain crop in the American world zone. Step three of the five-step model to explain the transition to agriculture is that humans in certain key regions of the globe were already adopting less nomadic lifestyles. and becoming at least part-time sedentary.
Archaeological evidence shows us that sedentism began to increase in some parts of the world from about 11,000 years ago. There were two main reasons for this, climate change and population pressure. As climates became warmer and wetter with the waning of the last ice age, in some areas there appeared regions of natural abundance where large numbers of humans settled.
It's no coincidence that the biblical Garden of Eden was probably located in southwest Asia, in the fertile delta regions of the Tigris and Euphrates. The people who settled in these regions were not farming, just living off the abundant natural fruits of the land. But this increased sedentism eventually led to overpopulation because sedentary peoples do not have the same constraints on population growth that nomadic peoples do.
Migration further contributed to the pressures of overpopulation because many of these same regions of abundance were also natural funnels for human migration. Southwest Asia is the only conduit for people moving between Africa and Eurasia, for example, just as migrants moving between the two large American continents had to pass through Mesoamerica. And this at least partly explains the large and dense populations that eventually settled in these regions. Certainly by 10,000 years ago, there is archaeological evidence that these inter-regional migrations had led to localised population pressure, which forced people to migrate through and settle in smaller and smaller areas. Now, we learned in the context of the ancient city of Jericho about communities that, as a result of climate change, the were able to abandon nomadism and adopt sedentism while still pursuing hunter-gathering lifeways.
Such communities are termed affluent foragers, foragers who have access to sufficient resources that they can settle down and become sedentized. Evidence of affluent foraging has also been found in many other parts of the world, including Australia. For example, the Gunditjmara people of Southeast Australia. abandoned full-time nomadism and settled down to build fish weirs, to farm eels and to live in sedentary villages nearby. But it is intriguing that despite this affluent foraging lifeway and the relative proximity of northern Australia to agriculturalists in New Guinea and nearby islands, Australian Aboriginals never made the transition to agriculture.
The most likely explanation for this is that Australian Aboriginals lived in a land of relative plenty. And with such an abundance of resources, there was simply no attraction in abandoning a successful nomadic lifeway for a more demanding, more stressful lifeway based on the cultivation of domesticates. But you'll remember that the most significant affluent foraging communities of West Asia were the Natufians, who began occupying the western fertile crescent, that is present-day Israel, Jordan, Lebanon and Syria, from about 14,000 years ago.
Natufian archaeological sites like Ein Malacha in Israel demonstrate that their diet consisted mainly of harvested and prepared wild cereal grains eaten as barley gruel and wheat flatbread. Ein Malacha also demonstrates that the adoption of sedentism led to increased population densities. Its population of perhaps 200 to 300 people, small by today's standards of course, made it perhaps one of the largest sedentary communities.
that had ever existed on the planet to that point in time. Because of affluent foraging then, particularly in the Fertile Crescent, population pressures resulting from sedentism and continuing migration forced human communities into smaller and smaller territories. By 13,000 BP, foragers were occupying a wide range of environmental niches all over the planet, and in some cases, these niches could not support increased populations, as Peter Richardson's intergroup competition model indicates. These groups were forced to try and feed themselves off rapidly diminishing parcels of land, and with further migration not really an option, they found themselves caught in what we call the trap of sedentism, step four in this five-step process. Remember, foraging lifeways are essentially nomadic in nature, requiring almost constant migration and sustainably small populations.
Imagine how difficult it must have been for migrating bands to support too many babies or elderly group members with reduced mobility. Survival in the Paleolithic just thus demanded the use of practices such as natural birth control, infanticide and senilicide. One statistic on this, some anthropologists have argued that perhaps 50% of all female newborn babies were killed by their parents during the Paleolithic. So populations of nomadic foragers grew very slowly. But once human groups became sedentary affluent foragers, these constraints on population growth simply disappeared.
It was no longer necessary to leave old folks behind, and communities were able to support more children, so populations grew amongst affluent foraging groups. This led eventually to the problem of overpopulation, a problem that would have become even more acute if climate change made affluent foraging less sustainable. Certainly, all the Natufian sites provide evidence of sedentism and increasingly dense local populations, suggesting that there may eventually have been too many people to support by affluent foraging practices, even at the level of intensification practiced by the Natufians. Faced with increasing populations, many communities were left with few alternative survival strategies. Because of continuing climate change and the resulting lack of space, A return to a nomadic foraging lifeway was impossible, and after many generations of affluent foraging, the skills of the nomadic hunter-gatherer may well have been lost.
The alternative was to concentrate on increasing the productivity of the crops and animals available to the community by removing unwanted trees or plants associated with weeding and deforestation, by planting, tending and harvesting desirable plant species, leading to domestication, and by tending and manipulating desirable and useful animal species, herding. In other words, the only viable option available for affluent foragers faced with overpopulation pressure and climate change was to intensify cultivation and adopt farming. And that's exactly what appears to have happened at sites that could support large populations, such as Jericho, Jammu in northeastern Iraq, and Çatalhöyük in Turkey.
The final step in this model then, step five, is the adoption of farming, the only remaining survival strategy available for these communities. This five-step model works very well in West Asia, particularly the Fertile Crescent, but let's conclude this lecture by seeing how well it applies to the emergence of agriculture in other parts of the world. In central China, the arrival of warmer, wetter weather following the waning of the Ice Age gave hunter-gatherers access to herds of wild cattle and sheep and to a range of wild grasses that appeared in great profusion, particularly green foxtail millet. Sites such as Shuguan, and Shuzetan excavated in the Fen River Valley provide clear evidence that the residents were pursuing affluent foraging lifeways, still surviving through hunting and gathering, but becoming sedentized.
Evidence of numerous sedentary Neolithic farming villages begins appearing in the region from about 6000 BCE, notably Sichuan and Peiligang, suggesting that these communities were largely surviving through the domestication of millet 8,000 years ago. In southern China, Along the middle reaches of the Yangtze River, a warming climate soon after 8,000 BCE led to an expansion of lakes along the river valley, which facilitated the spread of wild rice. Two sites in particular have provided evidence of the transition from foraging to farming. A cave at Diaotong Huan indicates that rice was probably being collected in the wild by foragers soon after 13,200 before present, but that it disappeared from the site during the younger dryass coal snap, when the plant itself may have been forced to retreat to the south just to survive. Wild rice then returned to the valley as the climate warmed again and was apparently being domesticated by the residents by at least 6,000 BCE.
So Dao Tong Huan, along with a second major cave site at Shan Rendong, provides indisputable evidence of the increasing availability of a domesticable crop species because of climate change. and of the adoption of sedentary lifeways by affluent foragers, which led inevitably to population increases and the eventual domestication of rice in the Neolithic era. In North, Central, and South America, the same general trend is found in the archaeological record. A climate-related increase in the availability of different food sources led to increased sedentism and subsequent population pressure, which in turn trapped humans into having to adopt more labour-intensive food.
cultivation practices, and eventually full-scale agriculture. The earliest crop species in the Americas were squash, followed later by common beans and the chili pepper. The Mexican sites of Zohapilco and San Andreas appear to have been occupied long-term by affluent foragers who eventually made the transition to farming, although the dates for this transition and for the first evidence of domestication remain difficult to pin down. In South America, the Tres Ventanas caves in the central highlands of Peru provide the earliest evidence of potato, gourd and sweet potato in the diets of affluent foragers living there. The appearance of the domesticated potato has been dated to roughly 5,500 BCE, although its domestication status is unclear because these species were also growing in the wild in this beneficial environmental niche.
Once the shift from affluent foraging to full-scale agriculture was made, virtually every South American site indicates the rapid development of complex sedentary societies and increased population densities, particularly along the Pacific coast. So the five-step model, a process driven by the critical prime movers of climate change and population pressure, generally works well in explaining the transition from foraging to farming. although there are some exceptions to the model.
Once humans were settled in communities with increasing populations, the only viable option open to them to feed themselves was intensified food production from the land available. And once these communities completed this complex transition from foraging to farming, human history suddenly found itself spiralling along an entirely new trajectory.