12.4: Agriculture and its Effect on Humans
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Modern humans (50,000 – 10,000 years ago) completed the migration to all the continents except Antartica, moving first into Australia, Eastern Siberia, the Pacific margins, Japan, and the Americas. Then from 10,000 years ago to 1,500 CE, humans arrived in the Arctic, the Indian Ocean, the deep Pacific, and tropical rain forests. Migration occurred in a “staccato” pattern with “easiest” areas colonized quickly, while more “difficult” areas remained uninhabited for thousands of years. A region’s “easiness” is calculated from estimates about available plant and animal biomass and net productivity—that is, how quickly it returns—in each habitat. For example, tropical savannas and grasslands of East Africa were colonized first as the biomass there sustained the first bipedal hominins.
While we know about when American colonization began, the pace and means of colonization are still debated. Complicating the discussion of timing is the fact that the Late Wisconsin Ice sheet blocked the overland route from about 30,000 years ago, when two sheets merged, up until about 12,000 years ago, when they opened after a thaw. At this point in time, only a handful of sites support possible pre-10,000 BCE occupation: Monte Verde in Chile, Meadowcraft near Pittsburgh, and Page-Ladson in Florida. As recently as 2015, excavations at Monte Verde and Chinchihuapi have strengthened the “possibility of an earlier human presence on the continent” to as far back as 17,000 BCE. This date has continued to move back in time as archeologists consider evidence of more mobile humans who did not leave large artifact clusters because of their ephemeral nature, but nonetheless may have been present before more sedentary groups.
For now, however, the clearest evidence for when the Americas were widely populated comes through the Clovis point, a specific arrowhead shape that was unique in its ubiquity and sophistication. The Clovis point was also found in mammoths that had grown extinct by 10,500 years ago, this discovery meaning that humans were common in North America by then. From Beringia, humans moved at a rate of roughly 10 miles a year until they reached Tierra del Fuego and fully populated the Americas.
Historian Lauren Ristvet defines agriculture as the “‘domestication’ of plants... causing it to change genetically from its wild ancestor in ways [that make] it more useful to human consumers.” She and hundreds of other scholars from Hobbes to Marx have pointed to the Neolithic Revolution, that is, the move from a hunter-gatherer world to an agricultural one, as the root of what we today refer to as civilization. Without agriculture we don’t have empires, written language, factories, universities, or railroads. Despite its importance, much remains unclear about why and where agriculture began. Instead, scholars hold a handful of well-regarded theories about the roots (pun intended) of agriculture.
Most scholars agree that the Ice Age played a fundamental role in the rise of agriculture, in the sense that it was impossible during the much colder and often tundra-covered period of the Pleistocene, but inevitable during the Holocene thawing. Only 4,000 years before the origins of agriculture, the planting of anything would have been an exercise in futility. During the Last Glacial Maximum (24,000 – 16,000 years ago), average temperatures dropped “by as much as 57 ̊ F near the great ice sheets...”
This glaciation meant not only that today’s fertile farmlands of Spain or the North American Great Plains were increasingly covered in ice, but also that other areas around the world could not depend on constant temperatures or rainfall from year to year. Pleistocene foragers had to be flexible. The warming trend of the Holocene, by contrast, resulted in consistent rainfall amounts and more predictable temperatures. The warming also altered the habitats of the megafauna that humans hunted, alterations that in some cases contributed to their extinction. Therefore, as animal populations declined, humans were further encouraged to plant and cultivate seeds in newly-thawed soil.
When we start to examine other factors that allowed humans to transition to agriculture, we find that the climate factor looms even larger. For example, agriculture was usually accompanied by a sedentary lifestyle, but we see communal living and permanent settlements among multiple groups of hunter-gatherers. Homo sapiens had also begun to domesticate animals and plants alike during the Pleistocene. Humans were already being buried alongside dogs as early as 14,000 years ago. As we’ll see below, gatherers were developing an increasing taste for grains long before they would abandon a foraging lifestyle. Essentially, humans were ready for agriculture when climate permitted it.
Generally speaking by about 8,000 years ago, farmers in West Asia (Figure) were growing rye, barley, and wheat. In northern China, millet was common 8,500 years ago. In the Americas, the domestication of maize began around 8,000 years ago in Mesoamerica, while at about the same time, Andean residents began cultivating potatoes. Once all of these areas realized agriculture’s potential as a permanent food source, they began to adapt their societies to increase their crop consistency and crop yields. We’ll discuss how agriculture affected societal development below.
The transition from foraging and collecting to cultivating took place over several centuries, but these gradual changes did serve to mark a very distinct era of permanent settlement during the Neolithic Period. Increased rainfall around 9600 BCE meant that the Jordan River would swell yearly, in the process depositing layers of fertile soil along its banks. This fertile soil allowed locals to rely on agriculture for survival. Soon after they founded Jericho just north of the Dead Sea.
Jericho’s residents did distinguish themselves from their hunter-gatherer predecessors, however, through their relatively extensive construction projects. They used mud bricks to build a wall that encircled the settlement probably for flood control, a tower, and separate buildings for grain storage. The former foragers now living at Jericho could rely on fish or other aquatic creatures for meat as they experimented with permanent settlement, but those foragers living further away from large bodies of water would need another source of meat. This need increasingly was met by animal domestication.
Effects of Agriculture
For the majority of our history, humans lived a nomadic lifestyle as hunter-gatherers. Near the beginning of the Neolithic, about 12,000 years ago, humans adopted a more sedentary lifestyle and gradually transitioned to a fully agricultural subsistence economy. This drastic change of diet and lifestyle had a dramatic effect on the overall health of Neolithic humans. Teeth are directly affected by diet and are a good source of information on the ways in which the dietary and food processing changes associated with the beginnings of agriculture impacted the general health of Neolithic peoples. By analyzing teeth from Neolithic samples, paleoanthropologists have observed a general trend of declining oral health among Neolithic people in comparison to their hunter-gatherer predecessors. The advent of agriculture is associated the reduction of tooth size, crowding, increases in caries, and increased occurrence of periodontal disease.
Hunter-gatherers maintained much smaller populations than early agricultural communities. Due to a diverse diet and smaller group numbers, hunter-gatherer societies had less potential for nutritional deficiencies and infectious diseases. With the advent of a sedentary agricultural lifestyle, Neolithic populations dramatically increased. Skeletal analysis suggests that these Neolithic peoples experienced "greater physiological stress due to under nutrition and infectious disease" (Ulijaszek 1991:271).
Cities and other large settlements appeared for the first time during the Neolithic. Pathogens require a large host to thrive and these large, crowded populations provided a human host population that had not previously existed among hunter-gather societies. Now able to spread easily from person to person in the crowded conditions of cities, pathogens were able to exploit entire groups and reach endemic levels
Crowded conditions paired with human settlements in close proximity to animals also contributed to high rates of infectious disease. In many early agricultural communities, animals were kept both near to and inside of houses. This proximity allowed some zoonotic diseases to transfer from animals to humans contaminated water sources and close contact with human waste also facilitated parasitic infection in both animals and humans.
Many early agricultural centers were dependent upon one to three crops and ate significantly less meat than their hunter-gatherer predecessors. Cereals such as barley, wheat, and millet, as well as rice and maize, commonly formed the subsistence base of early agricultural communities. Decreased variety of food also meant a decreased variety of nutrients in the diets of these people. Cereals contain little iron, but do contain phytates which are known to inhibit iron absorption. Maize is deficient in amino acids lysine, isoleucine, and tryptophan. Moreover, iron absorption is low in maize consumers, and... rice is deficient in protein which inhibits vitamin A absorption.
Evidence of infectious disease and nutritional deficiencies is found in Neolithic skeletal samples as skeletal lesions in the form of porotic hyperostosis and cribra orbitalia. Cribra orbitalia is a kind of porotic hyperostosis which occurs on the skull and is associated with anemia. Transitioning from a hunter-gatherer-based subsistence economy to an agricultural lifestyle not only changed the foods Neolithic peoples consumed, it also changed their workloads. A general trend of decreased stature reflects an overall decrease in health among agricultural populations of the Neolithic. Evidence of stunted growth can be seen on teeth in the form of enamel hypoplasia and on the skeleton in the form of growth arrest lines as well as osteopenia and osteoporosis.
Agriculture helped contribute to the development of class. Before agriculture, hunter-gatherers divided tasks like seed gathering, grinding, or toolmaking. However, without large scale building projects like aqueducts or canals required for agriculture, hierarchies were much less pronounced. The intensification of agriculture during the Neolithic required irrigation, plowing, and terracing, all of which were labor intensive. The amount of labor required could not be met through simple task division; someone had to be in charge. This meant the establishment of ruling elites, a societal grouping that had not existed during the Paleolithic. Social stratification is further evident as some Sumerians and even institutions, including temples, began owning slaves.
While violence certainly existed during the Paleolithic period, organized warfare was an invention of the Neolithic. Agriculture meant larger populations and settlements that were more tightly packed and closer to one another. These closer quarters created new social and economic pressures that could produce organized violence.
Family life also changed significantly during the Neolithic. Sedentary communities invested more time and resources into the construction of permanent homes housing nuclear families. People spent less time with the community as a whole and within homes it became easier to accumulate wealth and keep secrets. The shift in gender roles after agriculture seems to be even more pronounced, as the role of women became more important as humans moved out of the Paleolithic and into the Neolithic era.
The transition to agriculture in the Neolithic was arguably one of the most drastic lifestyle changes in human history. Changes in diet, living conditions, and subsistence activities had an enormous impact on human health, though effects varied from region to region. Skeletal analysis of these early agricultural communities suggests that the transition to agriculture had an overall negative impact on human oral health, increased the incidence of infectious disease and nutritional deficiencies, and contributed to an overall reduction in human stature.