Unit 1: Origins of Agriculture
Global Food Security
Food production figures and market prices vary greatly from year to year. To really understand the longer-term prospects for food security, it is important to focus on forces such as income and population growth, technological and environmental changes, and investments in agricultural infrastructure and research.
Recent food trends
It was estimated that 167 million children in the world were malnourished at the end of the 20th century. This represents enormous suffering and loss of human potential, despite tremendous advances in knowledge and technology that occurred during the century. There have been some improvements -- the figure was 187 million in the late 1960's. However, advances were uneven in different parts of the world. In sub-Saharan Africa, the numbers have increased over the same time period, and one-third of all children presently go to bed hungry.
Food insecurity persists, but not necessarily due to shortfalls in global food production. Cereal production increased dramatically in the past three decades, keeping pace with the rapidly increasing population. But again, the situation in different parts of the world was uneven. Argentina, Australia, Europe, and North America became major grain exporters, while other countries turned increasingly to imports for their food supply. Government subsidies in Europe and North America dramatically impacted the grain trade. In the late 1980's when subsidies were high, there was a glut of grain and prices fell. Reduced subsidies in the 1990's slowed the growth in production of cereals. Another important trend over the past thirty years was the dramatic increase in meat consumption worldwide. This was largely due to rising incomes in some developing countries.
Prospects for food security in 2020
The rate of increase in demand for cereals will decline, due to greater prosperity and changing food preferences in developing countries. The absolute demand for cereals will increase from 1843 million to about 2500 million metric tons in 2020.
The demand for meat will increase from 208 million to 327 million metric tons worldwide by 2020. Poultry will be in particularly high demand. Use of cereals, especially maize, as animal feed will also increase. Much of the increase in meat consumption will occur in the developing world. Even though demand will double in South Asia, Southeast Asia, and sub-Saharan Africa, per capita consumption will remain low in comparison to the developed world.
Demand for root and tuber crops such as cassava, sweet potatoes, and yams, will increase by 55 percent in the developing world, with greatest increases in sub-Saharan Africa and Asia.
Sub-Saharan Africa is likely to remain a troubled area in terms of food security. It is the only region of the world in which the number of malnourished children is expected to rise, rather than decline in the next 20 years.
Land and water resources
Although there is still some potential for expansion of farming to new areas in sub-Saharan Africa and Latin America, in other parts of the world, there is little opportunity for expansion to new agricultural land. At the same time, crop land is rapidly being lost to urban growth. More than one million hectares of arable land in the United States are paved over each year.
Increasing production will therefore require increased productivity per unit of land. But intensive farming and other activities have already caused serious degradation of crop land. Nearly 40% of the world's agricultural land is seriously degraded, which could undermine the long-term productive capacity of those soils. Almost 75% of crop land in Central America is seriously degraded, 20% in Africa and 11% in Asia.
Water availability for agricultural uses and water quality are declining.
After 2010, key aquifers in China, India, West Asia and North Africa may
begin to fail. By 2015, with rising water shortages and populations, a
projected 40 percent of humanity will live in water-stressed countries,
putting increasing pressure on global grain supplies (Worldwatch Institute,
Early Agriculture and Development
What is a crop?
Crops are plants that are grown and utilized for economic gain. There are two fields of science that involve the study of crop plants and how to grow them:
Crops may be grown for many purposes:
To begin our study of crops, we will first ask some questions about the beginnings of agriculture...
Why did the agricultural revolution occur?
Hunter-gatherers knew a great deal about the 'biology' of the plants and animals on which they depended, and many planted seeds of wild species. They knew how to detoxify poisonous plants, and how to use plants for medicinal purposes. Religious rituals often served to promote the productivity of important food sources. It was common for women to do most of the gathering and for men to do the hunting. Although this must have been a difficult way of life in many respects, hunter-gatherers enjoyed considerable leisure time in comparison to modern societies.
About 10,000 years ago, in the delta of the Tigris and Euphrates rivers in Mesopotamia (today Iraq), people began to grow crops and to adopt a more sedentary lifestyle. The change from subsistence patterns (hunting and gathering) to agriculture was the first ‘cultural revolution’ that impacted human behavior and societies.
Impact of climate change
Why did the revolution occur? The shift to food production is related to the end of the Pleistocene era and beginning of the Holocene era. The ice age retreated, and the world became warmer and generally wetter beginning about 14,000 BC. Parts of the Fertile Crescent became drier, making it possible to farm. By 10,000 BC, climates were essentially modern. While the Pleistocene had strong climate fluctuations over periods of 1,000 years or less, these fluctuations have been much smaller in magnitude in recent times. It has been suggested that the past 10,000 years have been a "lucky break" in terms of climatic extremes and volcanic activity.
Theories about the origins of agriculture
Nobody can say with certainty why agriculture arose, but here are some of the theories that have been proposed.
Domestication for religious reasons. Agriculture has a divine origin in the classical mythologies of all civilizations. The specific deities and circumstances vary greatly, but the themes are similar. Given this association between domestic plants and animals and religious beliefs, some researchers have proposed that plants were first domesticated for religious purposes. This theory is not widely accepted, but deserves consideration for some plants in certain circumstances. One example would be the cultivation of tobacco by several native tribes of the Pacific Northwest.
Population pressure hypothesis. According to this theory, agriculture was born of necessity when population density reached some critical threshold. If not limited by resources, population can easily double in a century or less. This is a popular hypothesis, but is not consistent with time scales of human and agricultural development. Hunter-gatherers tend to maintain populations that are well below the carrying capacity of the land.
The 'Inventor-genius' hypothesis. One widely developed model is that cultivation was an invention or discovery. An extreme level of innovation would be required to see agriculture as a better way to make a living, when it represents such a drastic change in culture. Once invented, the system is so obviously superior to gathering that it would spread rapidly. However, agriculture appears to have arisen independently with different crops in many places at about the same time, making this theory implausible.
'Settling in' hypothesis. The inventor is not a 'rare genius', but a careful observer of the habits of animals and plants. Foragers learn agriculture as they become more familiar with resources. The problem with this argument is that hunter-gatherers appear to have had all of the knowledge needed to farm, but apparently chose not to do so. The evidence is clear that gathering yields far more kilocalories per unit of energy expended than any kind of agricultural system. In fact, the more 'advanced' the agricultural system becomes, the less efficient it is in terms of energy balance. Mechanized agriculture produces energy deficits. So what is the incentive?
Food foragers will not normally develop agricultural (no incentive).
Climatic hypothesis. Agriculture is an inherently superior mode of subsistence, but some climate change trigger is required for it to become established. Climate change brought pre-adapted people and plants together in the Middle East. Alternatively, agriculture was initiated to escape famine or as a response to adverse environments. However, there is evidence that rapid climate changes within the Pleistocene completely rearranged plant communities. With short-term fluctuations in climate, it would be difficult for farmers to cope and agriculture would likely not arise. It takes 1,000 years or more for a complex plant-exploiting society to arise.
Combined climate-ecological hypothesis. Reduction in climatic variation during the Holocene made agriculture possible. Expanding populations of broad-spectrum foragers generated competition and innovation that drove evolution and agriculture. Ecological feedback determined which food plants foragers chose to domesticate.
(Harlan, 1992). Although agriculture started more or less simultaneously
(8,000-6,000 BC) in several parts of the world, circumstances were probably
quite different. Therefore, no single model will be satisfactory. The
most conspicuous difference between hunting-gathering economies and agricultural
ones is the size of human populations: farming takes more work, but it
can feed more people. In agricultural economies, children are an economic
asset: they provide labor, wealth (dowries, bride-prices), and security
for the aged. This creates a vicious circle: more people ==> more food
==> more work ==> more children.
Where and when did agriculture and major crops originate?
Earliest records indicate that agriculture developed some
10,000 years ago in the Fertile Crescent. Agriculture developed later
in other regions. Each region developed particular crops.
We will discuss the centers of origin for specific crops in more detail next week. For now, have a look at the figure below to get an idea about the time scale for crop domestication in different parts of the world.
Adapted from http://www.ngdc.noaa.gov/paleo/ctl/10k.html
The timeline for human and agricultural developments shown above represents the conventional wisdom about the time and place that certain crops were domesticated. Recent archeological evidence is raising questions about these ideas. For example, rice cultivation may have occurred around 11,500 years ago, which would put it on a similar timescale to the cultivation of wheat in the fertile crescent. In contrast, the corn cobs from Mexico that were formerly estimated to have grown about 7,000 years ago may be of more recent origin (about 5,500 years old). Newer dating techniques are also indicating that domesticated squash may have been cultivated in Mexico around 9,000 years ago. If you are interested in reading about some of these studies, see the articles on the domestication of maize, squash and other New World crops in the reference section at the end of this unit.
How were plants modified through domestication and cultivation?
Early farmers where adept at observing and selecting plants that had desirable traits. Successive selection of desirable plants changed the genetic composition of early crops. Agriculture progressed slowly. The Agricultural Revolution took about 4,000 years to go from food foraging to complete dependence on domesticated products. On an evolutionary timeline, this was a sudden, rapid event. Early farmers could have developed agriculture in stages:
Beginning use of species that ultimately became domesticated
Protection and weeding of naturally occurring plant communities
Gathering of seed, cultivation, plant selection, and associated genetic changes that lead to domestication
The domestication of crops changed the propagation habits of plants, making them dependent upon humans for reproduction. With these crops, more food could be grown per unit of land. Settlements became sedentary. The social and political complexity of societies increased, with a greater division of labor and an increase in material wealth. Thus, human society changed too as the result of plant and animal domestication.
1. Population pressures
With the end of a nomadic lifestyle, rapid increases in population occurred. Populations became concentrated in urban areas. Work specialization and social distinctions increased, and people began to accumulate wealth.
2.Dependency on a few plant species
Agriculture made human communities dependent on a relatively few crop species rather than on the many different kinds of plants which hunter-gatherers used. Human diets became more narrow, and in many cases less nutritious.
3. Greater vulnerability to weather
Dependency on fewer plants in turn makes agriculture a great gamble, as farming involves "betting" that weather conditions will favor the growth of the crops planted. Agriculture continues the ancient dependency of human life upon natural ecological systems, but it raises the odds of disaster in any given year.
4. Complete dependency on harvest times
To survive, agriculturalists have to gather all their food for the year at one or a few harvest times, rather than gathering year round. Planting and cultivating must also be completed in a limited period of time. Produce from their fields must be stored for the rest of the year, protected from moisture, vermin, and thieves, and rationed in measured quantities. These conditions created a new kind of life style.
5. Need for intense physical labor
Agriculture requires intense and sustained physical effort--"drudgery"--at several times of the year, and on a scale previously unknown. In the Near East, cereal-growing required back-breaking labor at both planting and harvest times. Both men and women had to work in the fields. These conditions encouraged the development of social as well as individual discipline.
Problems associated with agriculture
Hunter-gatherers could stay clean and healthy simply by moving frequently. Sedentary agriculturalists must develop means to dispose of their dead, of their food wastes and excrement, and the wastes of their livestock.
2. Population growth
Mobile hunter-gatherer groups used various means to limit their population densities. Agriculturalists, however, benefit from large families because more children mean more hands to help in the fields. After 10,000 years of this way of life, the human population is still expanding exponentially. Today, there are more than 6.2 billion people on the planet, almost all of them supported by agriculture.
3. Infectious disease
Infectious disease is a problem closely related to population density and to the difficulty of maintaining a sanitary living space. Human beings can share many diseases with domestic animals; so the clustering of both humans and animals together in villages created an ideal environment for pathogens. Epidemics, previously very rare, became a common part of the human experience.
Gradually, in response to these recurring epidemics of deadly infections, selected human populations of agriculturalists developed some immunity to specific pathogens. Many infectious diseases slowly lost their lethal effects. Today, the common "childhood diseases" such as mumps, measles and chicken pox are the relatively harmless descendants of once fatal diseases. This is evidence that human populations changed genetically in response to their new way of life.
4. Monoculture and soil depletion
Domesticated crops are often grown in monoculture (only one crop species in a field), replacing complex natural ecosystems that had been utilized by hunter-gatherers. This creates a system out of balance, where nutrients in the soil necessary for growing a particular plant are depleted. Over a relatively short period of time, growing a single crop can deplete even very rich soils. Many early agricultural sites became uninhabitable due to this problem, which is still of major concern today.
5. Pests and pathogens
Human farmers consciously alter the environment and "select" the plant qualities they need for food or fiber. Unwittingly, they also "select" any insect pests or pathogens that can live on the crop. Thus, paradoxically, by increasing their food supply, farmers simultaneously increase threats to their food supply.
Review the WSU web site on the Agricultural Revolution:
Take the quiz on this Unit on the Blackboard.
Due April 7th
Review materials from the reference section (or from other sources). In one or two paragraphs, respond to one of the questions below. Cite at least one reference that you used.
1) Describe a ritual or religious ceremony of a hunter-gatherer society (past or present) that enhances the productivity of one of their important food sources.
2) Would you rather be a hunter-gatherer or an early agriculturalist? Why?
Post your assignment as an attachment into the slot under Assignments and paste into the appropriate forum on the discussion board. Read the assignment submitted by at least one of your classmates and send them either a question or a comment regarding their submission.
Recommended self-study (optional)
Review the article by Rosegrant et al., 2001, on the Global Food Outlook [pdf file].
Betz, V. Early plant domestication in Mesoamerica. Athena Review, Vol 2 No.1: 24-31. http://www.athenapub.com/nwdom1.htm
Bryant, V.M. 2003. Invisible clues to New World plant domestication. Science 299: 1029-1030.
Gepts, Paul, 2002. Lifestyles of the Hunters and Gatherers.
Gepts, Paul, 1996. Why did agriculture start?
Harlan, J.R. 1992. The Golden Age. Chapt. 1 In Crops and Man, 2nd ed. American Soc. Agronomy, Madison, WI.
Harlan, J.R. 1992. Views on Agricultural Origins. Chapt. 2 In Crops and Man, 2nd ed. American Soc. Agronomy, Madison, WI.
Levetin, E. and K. McMahon. 2005. Origins of Agriculture. Chapter 11 in Plants
and Society, 4th edition. McGraw-Hill, New York, NY. Additional on-line
notes and references:
Pipperno and Flannery. 2001. The earliest archeological maize from highland Mexico: new accelerator mass spectrometry dates and their implications. PNAS 98: 2101-2103.
Rosegrant et al., Global Food Outlook: Trends, Alternatives, and Choices.