Agriculture: Why and How Did It Begin? Startups
INTRODUCTION
Today the world’s population exceeds 6000 million people, almost all of whom depend on agriculture for their survival, and yet growing crops and raising domestic animals is a very recent development in the history of humanity. Anatomically modern humans—Homo sapiens—began to colonize the continents as foraging hunter-fisher-gatherers some 100,000 years ago, but it was not until about 12,000 years ago that farming began to replace foraging as the main mode of human subsistence. It did so first, and very gradually, in the so-called Fertile Crescent of Southwest Asia.
In other regions of the world, such as central China, northern tropical Africa, and Mesoamerica, primary (independent) transitions from foraging to farming also occurred, even later than in Southwest Asia, but by 1500 A.D., when Europeans were beginning to expand overseas, most of the world’s population (estimated at 350 million) had become dependent on agriculture. From today’s perspective, this late emergence and very gradual development of agriculture may seem surprising. It prompts the question, why did it not occur much earlier, or, conversely, why did humans remain dependent on hunting, fishing, and gathering for so long?
This response stems from a deeply embedded and still prevalent assumption that the transition to agriculture was an inevitable stage in human progress. However, in the long perspective of humanity’s foraging past the question that demands an answer is not why did agriculture not develop sooner, but why did it develop at all? Before pursuing that question, we need to consider what precisely is meant by ‘‘agriculture,’’ because failure to define it, and other related terms such as cultivation and domestication, has led to confusion in attempts to explain why and how agriculture arose. Here, cultivation is defined as the sowing or planting, tending, and harvesting of useful domesticated or wild plants, which may or may not involve tilling the soil.
Domestication is defined as the genetic, physiological, and/or morphological alteration of wild plants that results from deliberate or inadvertent cultural selection and leads to the plants’ dependence on humans for their long-term survival. Agriculture is defined as the growing of domesticated crops by methods of cultivation that usually but not always involve systematic tillage of the soil. The distinction between cultivation and agriculture is particularly important because it enables us to differentiate between systems of crop production practiced by farmers and systems of wild-plant production practiced by foragers. Having clarified this distinction, we need next to consider how foragers have cultivated wild plants to enhance their productivity.
PLANT CULTIVATION BY FORAGERS
Many historical and ethnographic accounts of ‘‘hunter-gatherers’’ show that they not only gathered wild plants but often increased the productivity of selected taxa by such methods as controlled burning; vegetation clearance and weeding; harvesting, storing, sowing, and planting seeds, tubers, cuttings, and other propagules; and tilling, draining, and irrigating the soil.
Such practices can be regarded as forms of cultivation, but, although they are sometimes described as ‘‘protoagricultural,’’ they do not amount to agriculture (as here defined) because they rarely include fully domesticated crops. This distinction is not just semantic, because the ethnographic, historical, and more limited archaeological evidence we have indicates that cultivation by foragers was usually only minor activity in their hunting-fishing-gathering systems of subsistence.
Although many forager groups engaged in small-scale cultivation, it did not normally, and certainly not inevitably, lead to full plant domestication and the development of agriculture. However, that this did occasionally occur is undeniable, for if it had not, agriculture would never have arisen. So we must next ask what factors may have caused particular forager groups to invest more time and effort in cultivation and to become progressively more dependent for food and other products on suites of plants that underwent domestication and were transformed into agricultural crops, thus initiating primary transitions from foraging to farming.
FACTORS THAT MAY HAVE PROMOTED PRIMARY TRANSITIONS TO AGRICULTURE
Many factors, singly or in combination, have been proposed as causal agents that could have promoted crop domestication and the rise of systems of agricultural production. They range from factors external to the human groups concerned, such as natural climatic and vegetational changes, to social-behavioral ones such as reductions in seasonal mobility associated with the year-round, long-term occupation of settlements (sedentism) and the elaboration of storage techniques; population pressure; competition for scarce resources; differential access to food and other products associated with the development of social ranking; exchange and trade; and technological innovation.
Underlying the discussion of the relative importance of such factors is the more general question of whether the earliest foragers to develop agriculture were pressured into doing so by factors that induced subsistence stress or whether the process was a more random one by which some groups ‘‘drifted’’ voluntarily into progressively greater dependence on a narrower range of plants, some of which were domesticated. It is impossible to resolve such a general question conclusively by appealing to direct archaeological evidence of forager and early agricultural subsistence (which is in any case very meager), but the ethnographic and historical record strongly suggests that agriculture is more demanding of time and energy, and generally riskier than foraging, even when the latter includes an element of cultivation.
It, therefore, seems unlikely that foragers would have voluntarily and progressively become dependent on agriculture for their main food supply unless they were subjected to some form(s) of subsistence stress. There is ethnohistorical evidence that some foragers did select and sufficiently modify particular plants that became largely dependent on their cultivation for survival, and can be said to have been at least semi-domesticated, but what most foragers did not do was focus their energy on the cultivation, and domestication, of selected crops to such an extent that they became farmers. This evolutionary pathway appears to have been followed only by a few forager groups in the past whose livelihood came under sustained stress.
Such stress could have been generated by several of the factors already mentioned, such as climatic and vegetation changes, population growth, and competition between groups for scarce resources. Very probably, it was when several factors combined in particular situations to exert sustained stress on the subsistence practices of forager groups that transitions to agriculture took place. So we need next to ask in what contexts are this likely to have occurred.
THE CONTEXTS OF TRANSITIONS TO AGRICULTURE
There is little direct archaeological evidence that allows us to trace primary transitions from foraging to farming. Although it is possible to distinguish from their wild progenitors the remains of many domestic plants and animals recovered from sites of early agriculture, there are very few known sites that span and reveal such transitions. One that does is the Levantine site of Tell Abu Hureyra on the Euphrates River in Syria, where large assemblages of the charred plant remain from the Late Palaeolithic and Neolithic ages have been recovered and analyzed. Changes in the composition of the assemblages indicate a transition from the exploitation of the seeds of a wide range of wild plants, including grasses and herbaceous legumes, during the second half of the Late Palaeolithic (Epipalaeolithic) occupation c. 13,000–10,000 years ago, to the cultivation, by the Pre-Pottery Neolithic period at the site c. 9400– 7300 years ago, of a small number of domesticated crops, including barley, wheat (einkorn, emmer, and bread wheat), lentil, pea, and faba bean.
The evidence suggests that by the Epipalaeolithic period Abu Hureyra was occupied year round and that the inhabitants regularly harvested the seeds of the wild cereals and legumes. They probably began to cultivate them in response to an abrupt change to colder and drier conditions that began about 11,000 years ago and lasted until about 10,000 years ago (the Younger Dryas climatic interval) and progressively reduced stands of the wild plants from the least to the most drought-tolerant species.
Toward the end of the Younger Dryas, there is archaeobotanical evidence of increases in weeds typical of dryland cultivation, and through the succeeding Pre-Pottery Neolithic period (c. 10,300–7500 years ago) in the Levant as a whole the number and size of settlements increased in response to population growth, and the remains of the ‘‘founder crops’’ of Southwest Asian agriculture appear at an increasing number of sites.
By the end of the period, grain farming (and the herding of domestic goats and sheep) had become the mainstay of the human population of the Fertile Crescent, and the new agro-pastoral, village-based way of life had begun to spread outward, toward Europe, North Africa, and Central and South Asia. The Southwest Asian Fertile Crescent currently provides a uniquely detailed archaeological record of a primary transition from foraging to farming. It highlights the importance of the interaction of several factors in the process: climatic and vegetational change, sedentism and associated population growth, increased competition for declining food resources, and technological innovation (e.g., in the manufacture of sickles and grindstones).
We do not have equivalently comprehensive evidence for primary transitions to agriculture—as opposed to the spread of already established agricultural systems—in other regions of the world where distinctive combinations of plants (and in some cases also animals) were domesticated, such as China, southern India, New Guinea, northern tropical Africa, Mesoamerica, the Andean highlands, Amazonia, and eastern North America. (For a more detailed discussion of crop domestication in most of these regions, and in Southwest Asia, see the articles in this volume by Bar-Yosef, Delgado-Salinas et al., Asch and Hart, Lu, Pasquet, and Paz).
It is not yet possible to determine with confidence what factors may have interacted to induce foragers to become farmers in these regions, but there is some tentative evidence from central China that may implicate the Younger Dryas climatic interval in the transition from the harvesting of wild rice to its cultivation and domestication in the Late Palaeolithic and the widespread establishment of rice agriculture in the Neolithic.
In Mexico and Central and South America, however, there is little evidence of the Younger Dryas. Factors such as the establishment of sedentary settlements associated with population growth and social differentiation, resulting in more intensive exploitation of local wild foods, may have led to greater dependence on the cultivation of particularly productive plants, such as squash, maize, and beans, that ultimately became staple crops. In northern tropical Africa and eastern North America on the other hand, it is possible that short-term changes of climate (more recent than the Younger Dryas) may have stimulated the transitions to agriculture that occurred there later in the Early Holocene.
CONCLUSION
It appears that climatic change (to colder and drier conditions) was a key factor in the earliest known transition to agriculture in Southwest Asia. Such changes, in combination with increased sedentism, population growth, and other social factors, may have played an important part in transitions elsewhere. Progress toward a more complete understanding of the process requires the recovery, identification, and accurate dating of the plant (and animal) remains from archaeological sites that span periods of transition from foraging to farming. Very few such sites are known and even fewer have been investigated using modern techniques of excavation, dating, and analysis. Until more such research is accomplished, conclusive answers to the questions of why and how agriculture began will remain elusive.