CHAPTER 2 IN TEXT. Read chapter (1) also.

Important points to consider:
  1. We are absolutely dependent on plants.
    Ultimately, only plants can "harvest" the sun's energy by photosynthesis. All nutrients and energy are cycled.
    Although we tend to think that we are less dependent on plants today, this is partly a U.S. bias. This is not true for most people in the world. We are dependent on fewer species of plants than formerly, but even in the U.S. we are highly dependent on plants.

    Petroleum is the remains of former plants. What will we do when we use it up?
    In this course, we will talk about domesticated plants, gathered plants, and wild plants.
    Perhaps 10,000 plants (of possibly 250,000) are used by the peoples of the earth, but all human civilization depends mostly on 10 or fewer.

  2. The cultivation/domestication of plants began about 10,000 years ago.
    Text: page 41 ff. on dating methods.
    There were, perhaps, 10,000,000 people on earth at that time. By 2000 years ago, most of the major peoples and regions of the earth practiced agriculture.
    By 1900, there were 1.6 X109 people. Today there are about 6 X 10 9.
    Where did agriculture begin? Almost all of the oldest records are from the Near East. How do we know the plants they used were cultivated?

  3. Man was a hunter-gatherer before he began agriculture.
    In 1900, hunter-gatherers were restricted to small areas that were too dry, too cold or too wet for agriculture.
    Domesticated animals (dog, sheep, goat, cow) all arose about the same time as domestication of plants. Only about 50 animals were ever domesticated.
    These could have been linked to religion. Animals used to till fields mostly in the old world.
    Why did agriculture arise?

    Studies of present day hunter-gatherers indicate that they have considerable leisure time.
    In good areas, they don't have to learn to plant. Most hunter-gatherers eat (ate) plants. How do we know that? What was there? 12C/13C ratios, dentition, abrasion on teeth. Meat was an occasional luxury.
    Populations of hunter-gatherers usually maintained below carrying capacity.
    Cultivation may have arisen in the zones between sedentary and hunter-gatherer societies. Agriculture never arose in California and in the African savanna.
    Until recently, the !Kung bushmen of the Kalahari desert were gatherers. They mostly ate 14 plants. They recognize 105 species of edible plants. Their diet was quite good in protein and in total calories. They worked about 2.5 days per week to gather food. Agricultural societies work harder.

  4. There was an association of agriculture and sedentary society.
    On the other hand, some sedentary people never developed agriculture (e.g., fishermen).

  5. There was an association with cooking and with other detoxification of plants.
    Cooking made many plants more usable by man. Cooking arose before agriculture.

  6. Many hunter-gatherer societies know all they need to know about growing plants, but don't.

    Some gatherers do plant seeds. Some gatherers replant parts of root crops. Most cultures based on seeds, not root crops.
    Many root crops important in the lowland tropics. Some gatherers also irrigate. Gatherers learned how to cook and to detoxify foods in many cases.

  7. Some theories of origin of plant domestication:
    1. religious:
      Many peoples viewed agriculture as a gift from the gods.
      Some workers have felt that agriculture arose for religious reasons, i.e., for sacrifices (more probable for animals).
    2. "genius" or "eureka" theory (see "The Source" Mitchener).
    3. refuse heaps - Edgar Anderson
      This might have been especially true around houses or cattle pens. Both are also
      disturbed areas. Parts of the plants that were utilized were often discarded. Carl O. Sauer
      felt man had to be sedentary first. He favored SE Asia as the place of origin.
      But many nomadic peoples grow plants for food. The Near East center clearly did not develop in the tropics.
    4. "weeds"
      Edgar Anderson saw weeds as potential domesticates. They "preferred" disturbed habitats.
      Vegetative reproduction is favored in the tropics.

    Did agriculture arise as an extension of gathering?

  8. Our system requires energy input, whereas gathering produces excess energy.

Origins of particular crops
Alphonse de Candolle - in 1882, wrote a book on the origin of cultivated plants.
He based his ideas on historical writings, archaelogical information, ethnological data, linguistics etc.
N. I. Vavilov - added genetics, chromosome studies, and anatomical data. He was interested in the presence of wild ancestors.
Vavilov concluded that the most likely areas of origin were where the plant was cultivated and the wild ancestors grew.
Further, the areas of origin should be areas in which there was lots of variation. He decided that there were 8 major areas that met these requirements.
These were: Mexico and Central America, the Central Andes, Abyssinia, the Mediterranean, Indian (Middle East), SW Asia, China, and SE Asia.
Later, he added more till he got up to about 20 or so. At this point you couldn't really call all of them "centers".
Harlan concluded that there were three "centers": the Near East, Northern China, and Meso America and three other areas with diffuse origins (S.E. Asia, S. America, and much of Africa) that he called "non-centers".
Further, it had become clear that a "center of origin" often was not the same as a "center of diversity". Harlan concluded that it is very difficult to separate the origin and later expansion of a successful crop.

* Every model generated so far has evidence for and against it.
Some were for ritual, magic, ceremony, or religious sacrifice. Some were from "dumps". Some weeds gave rise to crops. Some crops gave rise to weeds.
Some weed-crop complexes had common progenitors. Some crops arose in Vavilov's centers, some did not.
Some people were sedentary before agriculture. Harlan proposed a "no-model" model. That is, he left room for a whole array of motives, actions, practices, and evolutionary processes.

Early agriculture
Many hunter-gatherers used fire to control or manage both plants and animals in their area.
Much agriculture by primitive peoples today is of the slash and burn type. Prairies and savannahs are difficult to farm.
Much agriculture is in the margin of forested lands. The advent of the steel plow made possible settlement of the prairies and plains in the U.S. and Canada in the middle 1800's.

Vavilov's Centers
Harlan's Centers and Non-Centers
Slash and Burn Agriculture in Venezuela

Revised January 2005

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© David S. Seigler, Integrative Biology 363, Plants and Their Uses, Department of Plant Biology, 265 Morrill Hall, 505 S. Goodwin Ave., University of Illinois, Urbana, Illinois 61801, USA. 217-333-7577.