The origins of agriculture from yet another area of fierce debate. At issue are not only the role of climate change, but also population growth and the morphology of plants or animals (e.g. the species exploited, site location and the relative importance of animals and plants in the food supply). What is not at issue is the main advantage of agriculture: it can support more people per unit area than living off wild resources. In addition, by staying in one place it is possible to gather more material possessions. The disadvantages are considerable. They include increased labour costs, reduction in the diversity of the diet, reduced mobility and less sharing of possessions. It establishes a less egalitarian social structure. In addition, living closer together and domesticating animals brings more disease. So the obvious question is why did hunter-gatherers take up food production? The most acceptable reason is that circumstances somehow forced them into agriculture, but there are starkly different opinions about what were the driving forces in this process.
Before embarking on this discussion, it is useful to define what we mean by agriculture. Many hunter-gatherer groups exploited the seeds and fruits from wild stands of plants. In so doing they developed means of storing what they had gathered to last them through times when food was scarce. The recent evidence from Ohalo II (see Section 3.13) suggests that this approach had been practised as early as 23 kya. This could have involved some degree of managing the resources by, say, removing weeds to enable the food plants to thrive. This first step along the road to agriculture (proto-agriculture) appears to have a long history. To make the important transition of starting to sow some of the harvest to cultivate a bigger crop in the subsequent year required settled conditions. It would be some 10 kyr before this happened. Even more important was the subsequent step that involved selecting those seeds that show improved properties, in terms of both yield and ease of harvesting. Over time this led to domestication of specific plants. In terms of archaeological evidence it is the presence of grains showing signs of having undergone this domestication process that is the crucial measure of the adoption of agriculture.
The history of the debate about the origins of agriculture usually starts with V. Gordon Childe, who developed the idea of the 'Neolithic Revolution'. He was a renowned synthesiser of archaeological thinking, who became Professor of Prehistory at Edinburgh University in 1927, and published two highly influential books: Man Makes Himself in 1936, and What Happened in History in 1942. He argued that agriculture arose as a consequence of abrupt climate change after the end of the last ice age. He proposed that this led to progressive desiccation that forced the withdrawal of humans, animals and plants to the banks of rivers and oases. The close contact that now prevailed between humans, plants and animals thus led to the first attempts at domestication. Where successful, this resulted in rapid population growth and the establishment of permanent settlements. His analysis took a rather simple view of how this challenge developed. Childe argued that the climate shifted from the cool wet conditions at the end of the LGM to the hotter, drier weather of the Holocene. This simplified approach does not tally with the changes that have been presented earlier. Moreover, it does not include a detailed interpretation of the impact of the complicated nature of this transition, with events like the Younger Dryas exerting particular influence over the move to agriculture.
The somewhat sweeping nature of Childe's 'catastrophic' explanation of the origin of agriculture ran into considerable resistance. Instead, a consensus formed around agriculture being the product of 'population pressure'. Around 12 kya hunter-gatherers began to produce significantly more offspring than they could feed. While population levels of hunter-gatherers are generally maintained at a 'carrying capacity', for whatever reason some palaeolithic populations began to grow. This increase led to an inevitable limitation of resources and made the adoption of the hardship and toil of agriculture inevitable. What was not clear was what drove the population explosion: why did hunter-gatherer population dynamics suddenly require people to embrace food production with all its laborious and time-consuming drawbacks rather than sticking to the freedom of hunting and gathering? Part of the story may be that sedentism and the more frequent use of settlements made child rearing easier. Women did not have to carry young children as part of a nomadic existence and this could have led to larger families. Even so, what was missing was some driving force behind the change, and needless to say, climate change seems to be an obvious possibility.
The two most important features of the period between the end of the LGM and the start of the Holocene are the dramatic changes in climatic conditions after Heinrich event 1 and shifts in the climate variability, notably the sudden decline after the Younger Dryas. The scale of the warming in the Bolling/Allerod period provided considerable opportunities for the most adaptable communities, notably in southwest Asia in what is known as the Fertile Crescent, to exploit the abundance that came with warmer temperatures and greater rainfall. There is also a suggestion in the figures that climatic variability declined somewhat during these warmer spells (see Fig. 2.9b), which may have permitted the establishment of a more settled existence in favourable locations. Although the Older Dryas interrupted this climatic amelioration, the period of amelioration probably provided the opportunities for populations in favoured areas to rise. The savage cold and aridity of the Younger Dryas brought this period of advance to a grinding halt. The return to near-ice-age conditions posed the most frightful challenge to the burgeoning communities of the Fertile Crescent. Driven to oases and riversides, they may have found agriculture the only option for survival.
Recent archaeological studies have provided evidence of climate change at the end of the ice age that supports the Malthusian interpretation of the origins of agriculture. This new information has come from the site at Abu Hureyra, on the Euphrates, in what is now northern Syria.
This site, which was probably an example of the Natufian culture (see Section 5.8), was established around 13.5 kya. Here there is an unbroken sequence of archaeological evidence stretching from hunter-gatherer times to full-blown farming. Recent results extend the evidence of domestic cereals in the region, which involve forms of wheat and barley, back before the conventional date of around 11-12 kya (Hillman et al., 2001). Now, it appears that systematic cultivation of cereals started at least as early as 13 kya: close to the beginning of the Younger Dryas.
The evidence indicates that hunter-gatherers at Abu Hureyra first started cultivating crops in response to a steep decline in wild plants that had served as staple foods for at least the preceding four centuries. The decline in these wild staples is attributable to a sudden onset of a drier, colder, more variable climate. Work by Gordon Hillman, of University College London, and his colleagues found that the wild seed varieties gathered as food gradually vanished, before the cultivated varieties appeared. Those wild seeds most dependent on water were the first to die out, then one by one by the hardier ones followed. So the hunter-gatherers turned to cultivating some of the foods they had previously collected from the wild. In an unstable environment, the first farmers started simply by transferring wild plants to more suitable habitats and cultivating them there.
The decreased annual yields of wild cereal stands drove people to adopt cultivation. This response probably occurred most naturally in areas where precipitation levels differed appreciably over short distances, notably in northern Mesopotamia. The other great advantage of this region was that several native grasses, notably wild barley, and einkorn and emmer wheat, grew in the mountains of eastern Anatolia and the Zagros Mountains. The process of domestication of these cereals was not the result of deliberate action. Higher yields came automatically from repeated cycles of sowing, growing and harvesting, which favoured heavier seeds and denser seed heads together with avoiding the propensity to shed seeds over an extended period. More deliberate action might have been a result of selecting grains that had less tough husks around the kernel, which would have been attractive as an aid to digestion.
It was not just a matter of grain cultivation. These radical effects of the Younger Dryas on human lifestyles are found in other evidence from the Levant. Hunting and gathering bands were forced to adapt to rapid climate change in the niches where wild plants and animals had formerly provided abundant subsistence. In the face of rapidly shifting conditions, subsistence strategies were extended to adjacent areas less affected by Younger Dryas drying and cooling. Archaeological findings reveal that the wild ancestors of all of the earliest, primary Neolithic crops grew together only in this Fertile Crescent region. Apart from the two types of wheat and barley, other plants that could be domesticated included lentils, peas and chickpeas. The wild chickpea provides a convincing key to the researchers' conclusions, as it is an extremely rare species occurring only in southeastern Turkey and northern Syria: had agriculture originated elsewhere, chickpeas would not have been domesticated as one of the first, or founder, crops.
While the earliest evidence of agriculture comes from the Fertile Crescent region, it is striking that the move towards agriculture occurred independently in other parts of the world at the beginning of the Holocene or even earlier. A consistent picture is emerging in South America, Mesoamerica, North America and China. Although cultivation may have been born first in the Near East, the latest evidence suggests that people on other continents began to domesticate the plants they lived with by the early Holocene - squash on the tropical coast of Ecuador (Smith, 1997) and rice along the marshy banks of the Yangtze in China (Shelach, 2000). Indeed the exploitation of rice may have pre-dated the Younger Dryas in East China. Fossil rice phytoliths have been identified from late glacial to Holocene sediments in the East China Sea that were probably transported by the Yangtze River from its middle or lower reaches (Lu et al., 2002). The phytoliths appeared first in the sequence at about 13.9 kya and disappeared during the period of 13-10 kya, which includes the Younger Dryas. The disappearance during the colder conditions suggests that this frigid period had a significant influence on human activities at the time. Warmer and wetter conditions before and after this near-glacial interval probably favoured rice domestication in the area. These results have changed archaeological thinking about the dawn of agriculture, moving it several thousand years earlier in these regions. All this suggests that the dramatic changes of the Younger Dryas were driving this movement. After the improvements of the Bolling and the Allerad, the challenges of radical switches in the climate before and after the Younger Dryas, combined with the consequent disruption of animal migration patterns, formed the trigger that made agriculture the only means of survival for many people.
Later developments included domesticating millet around 6 kya in northern China, while rice appears to have been domesticated independently in southeastern Asia around the same time. In Mesoamerica, maize [Zea mays) began to be cultivated about 7 kya, and was the 'miracle' crop that enabled large civilisations to develop, while in Peru the bean was domesticated around the same time. So, while the shifting pressures of the climatic changes around the Younger Dryas may have provided the initial impetus for the adoption of agriculture, in the long run the less variable climate of the Holocene was the vital factor in its survival. As noted in Section 2.8, humans emerged from the climatic 'long grass' and confronted the relative tranquillity of the Holocene landscape, at which point agriculture was the only option.
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