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    Why did agriculture begin and how did it spread from the ancient middle east?

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    The archeological party line points to the banks of the Tigris and Euphrates rivers. There, the authorities say that, about 10,000 years ago, humans suddenly learned how to sow and harvest such crops as wheat and barley. There, civilization really began. Or was it there?
    Wadi Kubbaniya, Egypt. At this site, G. Hillman, of the Institute of Archeology, London, has found grinding stones and tubers. This site is dated at 17,000-18,000 years old.
    New Guinea highlands. J. Golson, formerly of the Australian National University, has found ditches and crude fields in this area. The implication is that humans were tending plants here between 7,000 and 10,000 years ago.
    Buka Island, Solomons. While excavating Kilu cave, M. Spriggs and S. Wickler unearthed small flake tools with surfaces displaying starch grains and other plant residues. Evidently, these tools were used for processing taro. Further, the starch grains resembled those of cultivated rather than wild taro. Date: about 28,000 years ago.
    (Dayton, Leigh; "Pacific Islanders Were World's First Farmers," New Scientist, p. 14, December 12, 1992.)
    source: http://www.science-frontiers.com/sf086/sf086a02.htm

    When major climate change took place at the time of the end of the last ice age c.11,000 BC much of the earth became subject to long dry seasons. These conditions favoured annual plants which die off in the long dry season, leaving a dormant seed or tuber. These plants put more energy into producing seeds than into woody growth. An abundance of readily storable wild grains and pulses enabled hunter-gatherers in some areas to form the first settled villages at this time.

    The practice of agriculture first began around 8000 BC in the Fertile Crescent of Mesopotamia (part of present day Iraq, Turkey, Syria and Jordan which was then greener). This region was home to the greatest diversity of annual plants and according to one study 32 of the 56 largest grass seeds.

    The first crops to be domesticated were all crops of edible seeds, wheat, barley, peas, lentils, chickpeas, bitter vetch and flax. These plants were all readily storable, easy to grow and grew quickly. They had to undergo few genetic changes to be of use to farmers, their wild relatives remaining easily recognisable to this day. In several other regions world wide local crop domestication took place independently.

    In China rice and millet were domesticated by 7500 BC, followed by the beans mung, soy and aduki. In the Sahel region of Africa local rice and sorghum were domestic by 5000 BC. Local crops were domesticated independently in West Africa and possibly in New Guinea and Ethiopia. Three regions of the Americas independently domesticated corn, squashes, potato and sunflowers.

    Humans in many different areas of the earth took up farming in what is, set against the 500,000 year age span of modern humans, a very short time. This is the most convincing evidence that global climate change, and the resultant adaptations by vegetation, were the cause of the beginning of agriculture.

    Hunter gatherers
    We are wrong if we assume that the change from hunter gathering to farming bought an improvement in the quality of the human life or in the humans themselves. Skeletal evidence reveals that hunter gatherers were in fact, taller, better nourished, suffered less disease and lived longer than farmers. The gathering of wild grains produces more calories of food for each calorie of energy invested than any form of agriculture

    . Hunter-gatherers typically get more of their energy from gathering plant sources, usually done by women, than from hunting. Their diet is extremely diverse and thereby balanced, between 3000 and 5000 plants were gathered as food in North America. Hunter gathering humans had developed superior stone tool making skills, bone needles and fish-hooks, jewellery, art and music over 30,000 years prior to the advent of agriculture. We have discovered from the last remaining hunter-gatherer societies that these people have an encyclopaedic knowledge of plants and their uses and names for every species.

    No hunter gatherer would voluntarily change to farming. The practice of cultivation developed gradually in settled communities over thousands of years. Migrant mothers have to carry around their children and generally have longer birth intervals and lower birth rates than settled people. Increased population required increased food enforcing more reliance on agriculture.
    Settled agriculturists can survive at higher population densities estimated to be 10-100 times greater than hunter-gatherers.

    As well as the best available domesticable plants the Eurasian continental block was also the home of the major domestic farm animals. Sheep, goats and pigs were domesticated along with the first plants and surely attributed to the rise of the agriculturists. Around 6000 BC cows were domesticated and began taking on the burden of farm labour.
    However crop domestications took place in the Americas and New Guinea in the absence of any domesticable large mammals. When humans had first arrived on the these continents (Australia c.35,000 BC, Americas c.11,000 BC) they had quickly hunted into extinction these continent's native large mammals. Having not co-evolved with proto-humans these animals presumably lacked fear. At the time of the beginning of agriculture burgeoning numbers of highly skilled human hunters aided by dogs ( domesticated c.10,000 BC) caused serious depletion of wild game animals. In West Asia huge herds of gazelles had been decimated despite the fact that these animals can run at 50 miles per hour and jump up to 30 feet. This factor may have contributed to increasing demands on plant food sources and been an incentive to cultivate.

    How did humans domesticate plants?
    The mutation, which marks the beginning of domesticated crops, was the loss of wild mechanisms in grasses and legumes for the scattering of seeds. Humans selected for grains whose stalks had failed to shatter and legumes whose pods failed to explode. Simply by cultivating the seed which was easiest to collect humans unintentionally caused a genetic change in plants. The resultant plants, lacking any means of seed dispersal, could not have survived without human intervention.

    Annual plants had evolved ways to spread the germination of their seeds over several years in order to survive particularly bad weather. Seeds which sprouted immediately would have been the ones which were collected and then sown by the first farmers. Thus agricultural practice led to the loss of dormant seeds. Sowing and harvesting in bulk on the same occasion selected for plants that grew at more uniform rates.

    Farmers also selected for noticeable qualities such as size and taste. Different plants were selected for differing features such as bigger seeds, bigger fruits or oilier seeds. Plants which put more energy into the production of one part usually do so at the expense of another; squashes selected for larger fruit developed smaller leaves. Some plants were selected for different characteristics such as beets already grown in Babylonian times for their leaves (chard), beets were then developed for their edible roots and eventually in the 18th century for their sugar content. Corn, now one of the world's staple crops, may owe it's domestication to it's use in ritual and not as a food. Teosinte the probable ancestor of corn has a tiny seed enclosed in a hard coating. Farmers in Central America bred hundreds of distinct varieties of varied colours for differing purposes. Archaeologists debate how many 100's or 1000's of years corn cobs took to reach thumb size. Olives, flax, safflower, oil palm and rapeseed were selected for oil content. Hemp, fax and cotton were selected for their use as fibre. Domesticated their stimulants qualities were tobacco in North America, coca and mate in South America, coffee in Ethiopia and tea, ginseng and camphor in China. Some plants which produced poisonous compounds were domesticated from mutant individuals which lacked the poison. Wild relatives of almonds, potatoes, aubegines, watermelons, cabbages and lima beans were all too bitter or poisonous for human consumption

    Around 4000 BC the domestication of fruit and nut trees was made possible. These had resisted domestication because seed selected from desirable plants could not be relied upon to reproduce similarly desirable offspring. The discovery of propagation of cuttings overcame this problem in olives, figs, grapes and pomegranates. Apples, pears, plums and cherries had to await the development of grafting skills which originated in China.

    A change in the reproductive biology of cultivated plums, peaches, apricots, apples, grapes and cherries occurred when humans selected and bred mutant plants.. These plants became self-compatible hermaphrodites which could pollinate themselves. These plants could be relied upon to produce some progeny with the same characteristics of the parent making them more useful to ancient farmers.

    . The last major group of plants to be domesticated were plants that had began as weeds within fields of cultivated crops. These plants had adapted to the conditions of agriculture without cultivation by humans. These include rye, oats, turnips, beets, leeks and lettuce. . The collection and planting of seed in each village led to plants becoming adapted to localised growing conditions. Eventually this led to the creation of thousands of distinct varieties of staple food crops.
    How did plants domesticate humans?
    From the cultivated plant's point of view, the active assistance of humans was affording them a competitive advantage. The plants responded by evolving traits that increased their suitability for human cultivation. Plants have evolved many strategies to use animals to disperse their seed more efficiently than wind or water. The seeds of many wild species of plants must pass through an animal's gut before they can germinate. Some plants are reliant on just one species of animal to disperse their seed.
    The evolutionary changes of plants constantly interact with evolutionary changes in animals in a process of co-evolution. An example is 100 million years ago when there was a rapid co-evolution of insect species and flowering plants; the new flowering plants proliferated displacing the fern and conifer dominated flora. Herbivorous dinosaurs then evolved shorter necks to feed off vegetation that was closer to the ground

    By 6000 BC some societies were almost completely dependent on domesticated crops and animals. As agriculture produced more food than was necessary for subsistence it has been theorised that the practice of agriculture encouraged the division of labour, specialisation and the beginnings of a political elite. The concentration of stored food was a resource that could be seized and controlled by an elite, armies could be fed on the food grown by others thus giving power to Chieftains to engage in wars of conquest.

    The lack of varied chromosomal arrangements in the founder crops of the Fertile Crescent indicates that they derive from a single domestication process. Stone Age farming communities quickly spread across Europe and the Indian subcontinent. They brought with them their seeds, introducing their crops to regions where their wild ancestors could not have survived. The vast East-West expanse of the Eurasian continent assisted rapid movement of a package of crops adapted to the similar growing seasons of the same latitudes.

    By the time of Christ the crops of the fertile crescent crops grew over the 10,000 miles from Ireland to Japan. When European invaders arrived in what they termed the "new world" they adopted some indigenous crops such as Andean potatoes and New Guinean sugarcane. Where entire agricultural cultures were destroyed, such as the area currently the Eastern United States, locally domesticated crops were abandoned. Some of these crops which have remained obscure internationally offer great potential as food crops, such as Andean quinoa which is now becoming wider known.

    The original farmers who were still highly reliant on gathered food, utilised their knowledge of wild plants to discover all the plants whose cultivation offered greatest potential. This is borne out by the fact that they domesticated all the staple modern food crops. Diversity which took thousands of years to develop has been whittled away in less than a century. The legacy of crop diversity created by these ancient breeders is the basis of the security of the food supply to this day.

    Source: http://www.primalseeds.org/agricult.htm

    The theory of cultural invention assumes that once bioculturally capable, humans would inevitably develop agriculture, giving up animal-like methods and following the evolutionary process to more complex system. This theory assumes that to become agriculturists, people need to develop enough understanding of plants and animals or they must stumble upon this knowledge. However, foragers had advanced knowledge of their food sources, in some cases practicing cultivation, irrigation, periodic burning, and other manipulations. Exposure to agriculture did not always mean conversion; some groups of foragers lived nearby agricultural communities yet continued to practice hunter-gathering (1).
    A social model of agriculture, "competitive feasting," explains the change through societal interactions. In circumstances of "high food stress," foragers made alliances based on food sharing to prevent the depletion of resources. In rich areas of undepletable resources, however, sedentary societies formed and opportunities for competition increased. Thus agriculture developed to produce more food for the growing number of humans and their increasing competition for resources (2).
    Many explanations link the origins of agriculture with changes in the global environment. The "oasis theory" proposes that after the Pleistocene era, the last great glacial advance that ended about 12,000 years ago, a major period of desiccation occurred. Humans and animals sought refuge in oases that could support them, like the Fertile Crescent in Mesopotamia. The availability of potential domesticates resulted in the practice of agriculture, and thus settled communities and increasing populations (2). The proximity of protodomesticates may have caused coevolution, the mutual evolving of two interacting species. As humans modified the domesticates' environment, they created genetic changes that made the plant reproduce better in the altered environment. These same changes made the domesticates more attractive to humans, who would modify their behavior to favor the plant, increasing their food supply and thus their offspring (1).
    Another idea proposes that the long, dry seasons occurring after the Pleistocene caused adaptations in vegetation. The conditions supported annual plants that left dormant seeds or tubers. The abundance of these readily storable wild plants allowed for the first settled villages. For example, in the Fertile Crescent the first crop were edible seeds, wheat, barley, peas, lentils, chickpeas, bitter vetch, and flax, all which were easy to grow and to store, grew quickly, and had to undergo few genetic changes to be useful (3).
    Source: http://serendip.brynmawr.edu/biology/b103/f00/web3/partner3.html


    The Problem, and Some Alternative Solutions
    For tens of thousands of years, humans were foragers, yet in a relatively short period (ca. 10,000 - 5000 yrs ago) agricultural systems appeared in several widely separated parts of Old and New World, and by 2,000 yrs ago most human populations were dependent on agriculture [see Graph for time depth of foraging and agricultural systems, by region]
    This subsistence shift radically transformed human ecology, soc. org., demography, and even art and religion -- yet we still don't have a widely agreed-upon explanation for why (as opposed to how) it occurred
    Various hypotheses have been offered over last 50 years:
    1. Cultural Progress hypothesis is oldest
    It is based on assumption that agricultural life is inherently superior to foraging
    Assumes that once bioculturally capable (i.e., once Homo sapiens evolved), humans would inevitably develop agriculture subsistence as part of culturally-mediated progress from simpler to more complex, from arduous nomadic life to comfortable sedentary one, from wild to more and more "civilized" or "settled" state
    Archaeologist Robert Braidwood (1964) exemplifies this view; he portrays foragers as
    ...small groups of people living now in this cave, now in that...as they moved after the animals they hunted [with] no time to think of anything but food and protection...all in all, a savage's existence, and a very tough one. A man who spends his whole life following animals just to kill them to eat, or moving from one berry patch to another, is really living just like an animal himself. [quoted in Winterhalder 1993]
    The progress scenario also assumes that people needed lots of time to develop sufficient knowledge of plants and animals to permit domestication, or the good fortune to stumble upon this knowledge
    We now know that all foragers have very sophisticated ethnobiological knowledge; there are even a substantial number of cases where foragers cultivate, irrigate, prune, sow seeds, or otherwise manipulate wild plant foods, not to mention the ubiquitous practice of recurrent burning to encourage plant growth for direct consumption or to enhance browsing or grazing for animal prey
    We also know of cases where foragers are long-term neighbors of agriculturalists (e.g., Native Calif. adjacent to Southwest), and thus have access to both knowledge and domesticates, yet maintain their reliance on foraging
    Obvious conclusion from all this is that foragers needed motivation to develop or adopt agriculture more than they need knowledge
    Progress model assumes that motivation is obvious: agriculture would be less work, more reliable, and more productive than foraging
    But available evidence suggests that foragers do not necessarily work harder for subsistence, do not necessarily have less reliable resource base, do not usually face greater risk of famine (may even be lower), and do not consider their life inferior to that of subsistence agriculturalists or pastoralists; in fact, many have argued that foragers have easier and more fulfilling life than agriculturalists ("original affluence" view), though as discussed in earlier lecture notes and readings this is controversial
    In any case, there is little evidence that agriculture is more efficient (has higher yield per unit labor time) than foraging, and many of the wild ancestors of domesticated crops (grass seeds, small tubers, etc.), termed "proto-domesticates," appear to have been relatively low-yielding, inefficient resources
    As for greater productivity (yield per unit land) of agriculture, this is undeniably true, but only under specific ecological conditions, and only for fully domesticated resources that have been genetically modified to increase their yields
    The case against the "progress" hypothesis is quite strong, but this only accentuates the explanatory problem -- if foraging economies are so successful, and proto-domesticates so unrewarding, why the repeated and eventually worldwide shift to agriculture?
    2. Environmental change hypothesis also very popular in past
    First, there is the obvious correlation of agriculture origins with end of Pleistocene
    Terminal Pleistocene = time of rapid env. change, extinction of many game species, rise of sea level, rapidly warming climate, etc.
    However, closer look by archaeologists reveals problems with this hypothesis
    Not first time of major climatic change -- this occurred often in the Pleistocene (the geological epoch in which our genus evolved, lasting from about 2 million years ago to about 12,000 years ago)
    Second, agriculture arose independently at several times and places -- and in particular, quite a bit later (after end of Pleistocene) in the Americas [see timeline Graph again]
    However, recent detailed paeleoclimatological reconstructions (based on Greenland ice cores & deep-sea mud cores) indicate that during the late Pleistocene (last 100,000 years) climatic fluctuations were extremely abrupt on very short time scales (e.g., annual swings in mean temperature of 10º F. not unusual), and overall climate much drier, colder, and less rich in carbon dioxide (key to plant respiration) than in the Holocene (= last 12,000 years)
    Given this, some have recently suggested that agriculture was essentially impossible in the Pleistocene (Richerson et al. 2001)
    However, present consensus seems to be that while climate change may be factor in origins of agriculture, is not sufficient in itself
    3. Population pressure hypothesis most popular view in recent years
    It comes in several versions, but all share basic idea that population growth forces foragers to adopt agriculture, because wild resources become so scarce that eventually farming is worth doing
    Fundamental assumption is that agriculture has only one real advantage over foraging -- it can provide more food per unit land (tho at higher labor cost per unit food yield, and often lower nutritional quality)
    Getting more food out of given unit of land is termed intensification; the declining efficiency hypothesized or observed to result from intensification (because of higher labor costs) is example of "diminishing returns" (declining marginal output/unit input)
    Basic principle of diminishing returns w/ intensification applies within a subsistence mode as well as in shifts from one mode to another
    For example, adding low-ranked prey types leads to more total food harvested, but at lower efficiency (greater labor time per calorie or gram harvested)
    Population pressure model assumes that increase in population density will lead to greater competition for resources, thus decreased return per unit labor or even outright resource shortage
    In thinking about how population pressure might affect shifts from one subsistence mode to another, might expect that each mode has distinct "cost curve" [see Cost-curve graph, from Glassow (1978)]
    This model suggests there is a point at which it pays to add strategy B to the subsistence regime, or even to switch to pure B (e.g., from foraging to mixed or pure agriculture; from hunting to broad-spectrum foraging; from swidden to intensive agriculture)
    Reasons agriculture might be favored over foraging at higher population densities:
    1) crops, esp. seed crops, not as subject to overexploitation, whereas increased harvest and intensification of hunting or even of gathering may rapidly lead to depletion
    2) efficient foraging often depends on mobility, whereas opposite holds for agriculture (sedentism necessary to tend & harvest crops, store harvest)
    Main problem with population pressure hypothesis is timing -- why did it take thousands of years before population pressure came to head?
    Assumes very low growth rates or long-range demographic equilibrium for entire Pleistocene -- true in aggregate, but not necessarily for each local population
    I conclude that while the population pressure hypothesis is probably very important, by assuming rather than explaining the slow population growth or population stability of the Pleistocene, it in effect begs a key question about agricultural origins--why did it happen when and where it did?
    4. Coevolution is most recent major hypothesis about agricultural origins
    Coevolution refers to mutual evolutionary effects of two interacting species on each other; in this case, the two species or interest are humans (i.e., some particular population of humans) and a plant or animal "proto-domesticate" (PD for short), meaning a wild species that is beginning to be subject to domestication process
    Idea here is that certain ways of utilizing wild resources will cause the evolution of features that increase their yield to humans as a byproduct of increasing their own reproduction
    Interesting fact about many PDs is that they are opportunistic, "weedy" species that thrive in disturbed locales (e.g., around human settlements); also characterized by great genetic plasticity (favoring rapid "coevolutionary" response to human utilization)
    Coevolution hypothesis proposes that proximity of humans and such species would set in motion a process by which humans would modify environment of PD, favoring genetic changes in PD that would make it reproduce better in "disturbed" environment
    These same changes would make PD more attractive as human resource, and in turn humans would be selected (via cultural evolution) or motivated (via rational choice) to modify their behavior so as to favor PD propagation, because this would give them more food, and hence more offspring who in turn would continue the coevolutionary interaction
    For example, foragers harvesting wild barley or wheat PDs will necessarily harvest more of the variants that retain seed on stalk (tough vs. brittle rachis, to use the botanical terms)
    If in turn humans accidentally disperse this variety to new locales (e.g., spilling some seed in middens), or even purposefully plant it, the fitness of this variety will be enhanced and natural selection will favor evolution and spread of tough rachis independent of human intentional selection
    David Rindos (botanist turned anthropologist) has detailed several features of PD dispersal and fertilization that would likely be responsive to such coevolutionary dynamics
    While coevolution model is quite clever and plausible, it seems more a theory about how the domestication process occurred once it was started than why it got started in the first place; for agricultural origins per se, additional causes (e.g., climate change, population pressure, sedentism, etc.) would seem to be needed
    So once again we are faced with a model that is too general to explain specifics of why agriculture arose when & where it did, though it seems likely to be an important part of the answer to this question
    Will return to question of how to put various models together, but first let's briefly look at archaeological record of domestication
    Source: http://courses.washington.edu/anth457/agorigin.htm.

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