PLB143 - Lecture 10

Where did agriculture start?

© Paul Gepts 2012

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PLB143: Readings - Lecture 10

Some definitions

  • Center of origin
  • Center of domestication
  • Center of diversity

How did the idea of centers of origin evolve?

  • Alexander von Humboldt (1807): "The origin ... of the plants most useful to man and which have accompanied him from remotest epochs, is a secret as impenetrable as the dwellings of our domestic animals. "
  • Alphonse de Candolle (1882) Botanical knowledge: distribution of wild relative
  • Vavilov (1927) :
    • Centers of diversity --> center of domestication
    • 6-8 centers 
      • China
      • India
      • Central Asia
      • Near East
      • Mediterranean
      • Ethiopia
      • Mesoamerica
      • South America: Andes of Peru, Ecuador, Bolivia; Chiloe; lowlands: Brazil, Paraguay
    • All between 20-45 degrees latitude; mountainous regions, temperate climate
  • Centers of origin according to Zhukovsky (1968)
    • Megagene centers   
      • China
      • Indochina - Indochina
      • Australia - New Zealand
      • India
      • Central Asia
      • West Asia
      • Mediterranean
      • Africa
      • Europe - Siberia
      • Mexico & Central America
      • N. America
  • Vavilov's centers of origin

    (from Harlan 1971, © American Association for the Advancement of Science)
  • Zhukovsky's centers of origin

    (from Zeven and Zhukovsky 1975, © Centre for Agricultural Publishing and Documentation, Wageningen, the Netherlands)

The demise of the Vavilovian centers of origin

  • Why are not centers of origin centers of diversity any more?
    • Centers of diversity do not always occupy a limited area
    • The centers of diversity of different crops do not always coincide
    • There are secondary centers of diversity:
      • long history of continuous cultivation
      • ecological diversity
      • human diversity
      • introgression with wild relatives or between races of a crop

Where does this leave us?

  • Harlan's (1971) centers and non-centers
    • 3 centers (well-defined, limited area) coupled with 3 non-centers (vast area) 
      • Near East + Africa
      • China + S. E. Asia
      • Mesoamerica + S. America
    • Even in centers: peripheral centers:
      • Near East: Caucasus
      • China: much larger, more diffuse
      • Mesoamerica: N.E. Mexico, mid-Mississipi-lower Ohio, N.W. Mexico + S.W. USA
  • Harlan centers of origin

    (from Harlan 1971, © American Association for the Advancement of Science)

Harlan's most recent theory (1992)

  • Certain biomes or vegetation types may have been more conducive to domestication than others. In the next paragraphs, I first review what is a biome, which main biomes are recognized, and finally I consider in which biomes mots major crops originated.  (Information on biomes from D. Levin, Univ. of Texas, Biol. 304, Ecology and Evolutionary Biology ).
    • Definition of a biome

      A biome is a major regional terrestrial community with its own type of climate, vegetation and animal life. Biomes are not sharply separated, but merge gradually into one another over what is called an ecotone .

Description of major biomes


  • a polar desert
  • low rainfall and precipitation
  • slow decomposition
  • permafrost
  • long cold winters
  • short growing season (less than 60 days)
  • annual 0-24 hour change in daylength
  • treeless, low shrubs, sedges, mosses and lichens
  • special plant adaptations
  • slow to recover from disturbance
  • Wildlife: caribou , musk ox, polar bears
  • Main types:
    • Arctic tundra;
    • Alpine tundra ;
    • Tropical alpine.
  • Tundra in S. Hemisphere? Cool Antarctica
  • Alpine tundra

  • Tropical tundra


The Tundra
Tundra: The Not-So Barren Land

Evergreen Coniferous Forest (Taiga, Boreal Forest)

  • south of tundra, broad ecotone
  • cool summers, extremely cold winters
  • 16-24 inches of rain
  • acidic podzol soils
  • growing season 50-100 days
  • dominated by conifers (spruce, fir, larch, pine), few deciduous trees
  • only 2 layers, dense and shady
  • low diversity
  • moose, wolves, lynx, porcupine, grouse, warblers
  • susceptible to effects of acid rain, major source of wood for paper
  • Main types:
    • Boreal forest
    • Montane coniferous forest
    • Temperate "Rainforest"
  • Montane Coniferous Forest


Taiga Rescue Network

Temperate Deciduous Forest

  • Eastern N. Amer., Europe, China
  • well defined seasons; 5-6 month growing season (150-200 days)
  • 30-60 inches of rain
  • soils fertile, lots of leaf litter
  • dominated by broadleaf deciduous hardwood trees (oak, hickory, maple, ash, beech etc)
  • 3-5 layers, relatively open with rich ground flora
  • bear, deer, bobcats, raccoon, squirrels, many birds and invertebrates
  • original forests mostly cut down, 2nd growth remains

  • Temparate deciduous forest


Sierra Club: Southern Appalachian Highlands Ecoregion  
Sierra Club: Northern Forest Ecoregion
Sierra Club: Interior Highlands Ecoregion

Grasslands (Prairie, Steppe)

  • Occurs in interior of continents and rainshadows
  • continental climate, hot summers, cold winters
  • rainfall 15-30 inches
  • frequent drought, fire and intense grazing
  • tallgrass prairie has fertile soil with a thick black layer high in organic matter, shortgrass prairie has much thinner soil
  • mixture of grasses and forbs, few trees except along streams
  • effect of burning
  • bison, antelope, (horses, camels, elephants) prairie dogs, coyotes, badger, prairie chickens, meadowlark
  • Main types:
    • Tall grass prairie (needs to be burned or returns to forest, now mostly plowed up) 
    • Shortgrass prairie (dry areas and deserts, reverts to thorny brush or desert when overgrazed)
  • Prairie

    (photo© K.R. Robertson 1995, Illinois Natural History Survey)

Sierra Club: Great North American Prairie Ecoregion
Konza LTER Home Page
Tallgrass Prairie in Illinois
Grassland Management with Prescribed Burning


  • latitudinal position between 20-30&degree
  • N and S of equator, and also in rainshadows
  • evaporation exceeds rainfall; very dry, 1-10 inches per year
  • hot days, cold nights
  • open plant cover, depends on rainfall,
  • some grasses, shrubs, cacti, creosote, rosette plants
  • many plant adaptations:
    •    deep or spreading roots, succulence
    • lose leaves
    • thorns
    • poisons
    • annual habit (seeds)
    • CAM plants: exchange CO2 at night
  • convergence of desert plants and animals
  • mammals mostly nocturnal, reptiles and snakes
  • desertification
  • N. American deserts:


  • Reduced leaf size or loss of leaves: Ocotillo

  • Sonoran desert: Anza Borrego State Park, CA

    Oasis in the park

Dry shrubland: Chaparral or Mediterranean

  • Western coastal regions between 30-40 N and S
  • Areas have the same climate, hot dry summer and cool, moist winter (6 months for each approx.)
  • Soils thin, rocky; highly weathered
  • Frequent fires, chaparral is a "fire climax"
  • Aromatic herbs, shrubs, sclerophyll leaves, scrubby trees, more oaks in areas with more rain: e.g., Sierra Nevada foothills
  • Some have high diversity
  • Plants adapted to fire:
    • resprout from thick, underground structures
    • bark protection
    • seeds require fire to germinate
  • Exploited for centuries, overgrazed by goats

Sierra Nevada foothills (CA)


Tropical Savanna

  • areas in dry tropics and subtropics in which grasses are conspicuous
  • often on either side of the rainforests
  • dry parched season (4-8 month drought) and rainy season
  • seasonally dry, tropical grasslands with scattered trees ( from Fred Morris, Gnu Photos ), thorny shrubs, Acacias, Eucalypts, Baobab
  • large herbivores in Africa (giraffes, zebra, wildebeests etc), ostrich, termites
  • fires are an important management tool; overgrazing leads to desertification
  • Savanna:

Tropical Deciduous Forest

  • forest in which trees lose their leaves for part of the year
  • has a pronounced wet and dry season
  • trees often thorny, shiny bark
  • relatively open, stratification and diversity lower than evergreen forest
  • Threatened by clearing for grazing, soils easily eroded.

Tropical Evergreen Forest

  • Warm, moist tropical lowlands
  • high temperature and rainfall, rainfall always over 60 inches/year (up to 160 inches), predictable daily cycle of cloud buildup and rain
  • soils highly weathered, reddish, high in aluminum and iron
  • rapid decomposition, nutrients cycled fast, stored mostly in plant biomass
  • high diversity
  • lots of tall trees, many evergreen species with no protection against drought or cold
    • drip tips
    • plank buttresses
    • dark interior
    • lots of layers
    • epiphytes, vines (lianas)
  • monkeys, sloths, parrots, toucans, bats, tapirs, frogs, lots of insects
  • major threats from logging and clearing for grazing and agriculture (coffee, bananas, rubber)
  • high population growth in countries where they occur
  • Tropical evergreen forest

    (from R. Crang)


Distribution of biomes

(figures from R. Crang, reference above)

  • Geographic: 
  • Average annual temperature and rainfall: 

Potential of biomes for agriculture

  • Tundra, taiga
  • Temperate prairies
    • sunflower
  • Temperate steppes
    • proso millet
    • foxtail millet
    • hemp
    • Triticum tauschii: donor of D genome of bread wheat (AABBDD)
  • Tropical rain forest
    • sugarcane
    • banana & plantain
    • orange
    • mango
    • cacao
  • Deserts
    • date palm
  • Temperate forest
    • fruits & nuts: apple, pear, cherry, grape, walnut
  • Tropical highlands:
    • principally Andes: often root crops: e.g., potato
    • also East Africa: Arabica coffee
  • Sea coasts:
    • coconut
    • cabbage
    • beet
    • cotton
  • Mediterranean woodlands & tropical savannas:
    • >50% of major crops: 
    • long dry season: Med.: summer; savanna: winter
    • Mediterranean:
      • 30-40 Lat
      • wheat, barley, pea, rapeseed
    • Savannas:
      • seed annuals or tuberous perennials: tuber remains dormant during dry season
      • maize, rice, sorghum, cassava, sweet potato, bean, peanut, yams

In the next sections, you will find an overview of agricultural centers of origin with examples of crops originating in them.

The Mesoamerican and North American centers of origin

  • Mesoamerican:
    • Cereals
      • Maize
    • Pseudocereals
      • Amaranth, chenopodium, chia (Salvia)
    • Grain legumes
      • Phaseolus beans
    • Roots & tubers
      • Sweet potato, cassava, jícama
    • Oilcrops
      • Cotton
    • Fiber
      • Cotton, agave ("sisal")
    • Fruits
      • Papaya, avocado, guava, prickly pear
    • Vegetables and spices
      • peppers, squash, tomato, vanilla
    • Stimulants
      • Cacao
  • North America
    • Roots & tubers
      • Jerusalem artichoke
    • Oilcrops
      • Sunflower
    • Fruits
      • strawberry, grape, cranberry, pecan
    • Stimulant
      • tobacco
Mesoamerican and North American centers

The South American center of origin

  • Pseudocereals
    • amaranth, chenopodium
  • Grain legumes
    • peanut, Phaseolus beans, jack bean, lupins, Inga spp.
  • Roots & tuber
    • arracacha, achira, cassava, jicama, oca, potato, añu, yacón, ullucu, mashua, unchuc
  • Oilcrops
    • peanut, cotto
  • Fibre
    • cotton
  • Fruits & nut
    • cashew, pineapple, guanábana, cherimoya, Brazil nut, papaya, avocado, guav
  • Vegetables & spice
    • pepper, squash
  • Stimulant
    • coca, maté

The Southeast Asian center of origin

India, Indochina and the Pacific Islands as center of origin

  • Cereals
    • Asian rice
  • Pulses
    • pigeon pea, jack bean, winged bean, moth bean, rice bean
  • Roots & tubers
    • yams, arrowroot, taro
  • Oil crops
    • coconut
  • Fruits & nuts
    • bread fruit, orange, lime, tangerine, grapefruit, mango, banana
  • Vegetables & spices
    • cucumber, nutmeg, eggplant, plantain
  • Fiber plants
    • coconut, jute

The Chinese center of origin

  • Cereals
    • Asian rice, proso and foxtail millets
  • Pulses
    • soybean, adzuki bean
  • Root & tuber crops
    • turnip, yams
  • Oil crops
    • rape seed
  • Fruits & nuts
    • Chinese hickory, chestnut, quince; persimmon, litchi, apricot, peach
  • Vegetables & spices
    • Chinese cabbage, ginger
  • Stimulants
    • tea, ginseng, camphor

The African center of origin

  • Cereals
    • African rice, pearl millet, sorghum, tef, fonio
  • Pulses
    • cowpea, Bambara groundnut, hyacinth bean, Kersting's groundnut
  • Roots & tuber crops
    • yam
  • Oil crops
    • oil palm, castor bean
  • Fruits & nuts
    • baobab, watermelon, melon
  • Vegetables & spices
    • okra, Sesamum sp. (leaves), Solanum spp.
  • Fibers
    • kenaf
  • Stimulants
    • coffee

The Near Eastern center of origin

  • Cereals
    • wheat, barley, rye, oat
  • Pulses
    • pea, chickpea (garbanzo), lentil, lupine
  • Root & tuber crops
    • turnip, carrot, radish
  • Oil crops
    • rape seed, safflower, flax, olive
  • Fruits & nuts
    • fig, walnut, date palm, almond, grape, apple, pear, plum
  • Vegetables & spices
    • onion & relatives, lettuce, saffron, parsley
  • Stimulants
    • poppy, digitalis, belladonna, licorice

Classification of crops according to type of center of origin and dispersal (Harlan 1992)

Endemic: origin in a limited area + no spread from center of origin

E.g., Panicum sonorum in Mexico, Bitter potatoes in the Andes

  • Example of an endemic crop: the bitter potatoes of the Andes (Hernández Bermejo and León (1992): pp. 152-157; National Research COuncil (1989): pp. 99-100)
    • Solanum x juzepczukii: triploid: 2n=3x=36, S. x curtilobum: 2n=5x=60
    • Grown at 3,000 - 4,200m; 6-14ºC (but resistant to -5ºC); P=400-1400mm over 5-6 months
    • Bitterness: glycoalkaloids; removed by treatment --> "chuños"
    • Between August and March: 70% of diet on Altiplano ; stored indefinitely; soups and stews
    • Chuño preparation:
      • 1 day: spread out materials
      • 2-4 days: expose to frost (night) , trample to extrude water 
      • 10-20 days: spread out to dry
        --> chuños: freeze-dried potatoes 

  • Bolivian altiplano

  • Chuño preparation:
    • trampling to extrude water

    • drying
    • end-product

Semi-endemic: origin in a limited area + some dispersal

E.g., Eragrostis tef (tef) in Ethiopia, Oryza glaberrima (African rice) in W. Africa, Oxalis tuberosa (oca) in the Andes

  • Example of a semi-endemic crop: Oxalis tuberosa or oca of the Andes (Hernández Bermejo and León (1992): pp. 147-150; National Research Council (1989): pp. 83-91)
    • Oca <-- quechua: oqa or ok'a; 2nd most important root crop  in the Andes after potato; tolerant of harsh climates and poor soils 
    • Highest diversity for cultivars and wild relatives: central Peru (10ºS. Lat.) --> N. Bolivia (20ºS. Lat.): Variation for tubers, mainly:
      • color of skin and flesh: white, yellow, red, black
      • no. and depth of "eyes"
      • other traits: e.g., stem color: 
    • Dispersal: to Venezuela (8ºN. Lat.) and N. Argentina and Chile (25ºS. Lat.): before 1492 to Mexico: 200-300 BP: "papa roja"; to New Zealand: 20 BP: "New Zealand yam": photoperiod insensitivity!
    • Nutritional and culinary characteristics:
      • source of carbohydrates, Ca, Fe
      • flavor: from slightly acid to sweet
      • preparation: boiled, baked, fried, mixed fresh with salads, pickled with vinegar left in sun: increase in sweetness (glucose)

  • Oca:
    • Plant

    • Field

    • Tubers

    • Variation for stem color

Monocentric crop: Definable center + wide dispersal but without secondary center

E.g., usually new plantation crops: Coffea arabica , Hevea brasiliensis, Mangifera indica

  • Example of a monocentric crop: Hevea brasiliensis (rubber tree) (Sauer 1993: pp. 62-66)
  • Production:
  • Main source of natural rubber: Hevea brasiliensis
    • 9-12 species of Hevea
    • all from Amazon hybridize among themselves (limits: ecological specialization, flight distance of insects, flowering time)
    • natural rubber: polymer of isoprene (C5H8)n
    • constituent of latex (aqueous suspension) flowing from concentric latex vessels in phloem; initially a defense mechanism?
    • accessed by "tapping": cut in outer bark , cutting needs to be done carefully to maintain production 
    • until 19th century, no major effects of humans on Hevea; then, first plantings, in response to increased demand
    • improved processing of latex:
      • identification of solvents: --> air mattresses, rollers, raincoats (Mackintosh)
      • vulcanization: brittle and har when cold; sticky and soft when hot; heating rubber with molten sulfur --> hoses, drive belts, gaskets, tires
        ==> rubber boom (1910: 2$/lb) in Amazonia: e.g., city of Manaus 
    • development of rubber plantations in S.E. Asia
      • British collected 70,000 seeds in Amazon in upland site, highly productive grove, no other species in vicinity
      • 2,800 seedlings at Kew Botanical Garden --> Sri Lanka, Singapore, Indonesia
      • basis for further breeding for enhanced yield
      • Hevea: alternative to coffee
    • Why so little in Brazil?
      • only from wild stands
      • fungal leaf disease (Microcyclis ulei ) prevents intensification; breeding unsuccesful
      • shift of cultivation southward to drier areas

  • Tapping of latex

    (© Kees van Zon 1995 )

  • Tapping scars on tree trunk

    (from Treetap, Brazil Homepage )

  • Opera house in Manaus, Brazil

Some related sites of interest

Oligocentric: definable center + wide dispersal + one or more secondary centers

E.g.,: Near East complex: wheat, barley, pea, flax, lentil, chickpea, oat; secondary centers in Ethiopia, India or China

  • Example of an oligocentric crop: Cicer arietinum (chickpea or garbanzo)
    • Production: Asia: 92%; India: 75%; Pakistan: 10%
    • Cicer sp. : ~ 40 sp. in west and central Asia
      • C. reticulatum (Turkey): only species that interbreeds with C. arietinum
      • Archaeological record:
        • Turkey: 5,450 BC; Mediterranean: 4,000-3,000 BC; India: 2,000 BC; Ethiopia: 1,000 BC
      • Dispersal: divergence into two types:
        • Kabuli: to West (Mediterranean): large, clear-colored, owl-headed seeds; little wrinkling of testa; tall plants
        • Desi: to East (India): smaller, dark-colored, ram-headed seeds; wrinkled testa; smaller plants; two introductions? two different types of name: Sanskrit (land), Dravidian (sea)

Noncentric: Domestication over a wide area

E.g., sorghum, common bean, Brassica campestris

  • Example of a non-centric crop: Sorghum bicolor (sorghum) from Africa
    • Wild ancestor: Sorghum bicolor subsp. arundinaceum
      • distributed over the entire continent S. of Sahara
      • savanna grass; C4 photosynthesis: high temp., limited moisture
      • Staple food and beer grain in Africa; Staple food in India; Animal feed elsewhere
    • Cultivars: multiple centers of diversity and races (parallel with wild): 
      • most primitive race: bicolor
      • Ethiopia-India: race durra
      • E. Nigeria - Chad - W. Sudan: caudatum, guinea-caudatum, durra-caudatum
      • W. Nigeria - Senegal: guinea
      • Tanzania - S. Africa: kafir
      • --> suggests multiple domestications?

  • Domesticated races of sorghum

    (from J. Hancock)

Centers of origin and diversity - Conclusion

  • Analyze each crop individually: very different patters of genetic diversity and dissemination
  • Be aware of newer research results: change in outlook

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