PLANTS AND PEOPLE - Biology 328 - LECTURE NOTES
Hugh D. Wilson 

Origins of the Ethnoflora

1. Origins of the Ethnoflora (start)

Define: Flora, Ethnoflora [wild, cultivated, domesticated] - once thought that pre-historic people were hunters (lithic artifacts-Clovis-Mammoths) - it now appears that a 'hunter-gatherer' subsistence pattern was common (flotation analysis - more plant remains) - and early humans were very close to the local flora - used for food and anything else. WILD - ETHNOFLORA: CULTIVATED, WEED, PARTIALLY DOMESTICATED (GENETIC CHANGE), FULLY DOMESTICATED (DEPENDANT ON MAN FOR SURVIVAL). Classification: as boundary between domesicated and wild types become better defined (crossing, molecular methods), our symbolic links to these entities (names) will change to better reflect biological/phylogenetic relationships - gene flow - introgression - - example: Cucurbita texana vs. Cucurbita pepo - Zea mays vs. 'teosinte'  

2. WHEN?:  Domesticated plants are biological artifacts, each with its individual history and that history is directly connected with distinct human cultural/biological lineages. From an evolutionary point of view they are very young lineages: first fully domesticated plants date to around 10,000 BP - were fully domesticated at this time. Thus, human selection - maybe 15 - 20,000 BP. RADIOCARBON DATING (Willard Libby - 1949 - Nobel Prize in 1960): carbon 'fixed' in chloroplasts, is composed of a constant ratio of isotopes [12C and 14C - they differ in molecular weight, 14C is generated by interaction of cosmic rays and N2 in the atmosphere] as they occur in the atmosphere. When fixation ceases [the plant dies], 14C decays at a constant rate, i.e., the 12C /14C ratio changes at a known rate (14C degenerates back to N2 with a half life of ca. 5,700 years). Thus, plant material from archaeological sites can be dated [500 to 60,000 yrs]. Recent use of accelerator mass spectrometry (AMS) has provided a great advance - more accurate using less material, often from the plant in question. As opposed to comment in your book about revisions based on AMS - note Science 276:894 (confirms very early date - ca. 10,000 BP for domesticated Squash in Mexico) and keep in mind that statements regarding antiquity/origin/dispersal of agriculture are estimates based on available (often scanty) data from the archaeological records. FLOTATION analysis usually produces carbonized plant remains that can be dated in this way and recent use of this technique is generating new data and perspectives.

3. WHY?:

a. Carl Sauer (traditional view) - man moved from nomadic life style of huntng and gathering (annual rounds) to a sedentary pattern, perhaps at centers of ecological diversity in tropical, coastal areas (fishing). Once stabilized, leisure time provided by 'easy' life style allowed experimentation with food resources. The notion of CULTIVATION arose in these centers and - because in was inherently efficient - was actively developed via 'discovery' and spread from these centers as a 'logical' pattern of cultural development. Or (Edgar Anderson) - accidental (dump heap) but locical move to the more efficient (agricultural) way of life.

b. BUT - research on extant human populations living in 'hunter/gather' mode (Devore and Lee - !Kung Bushmen of the Kalahari Desert in Africa and Jack Harlan) has revealed that agricultural activities (planting, harvesting, ad processing) are LESS efficient and LESS fun than living off the land in a traditional hunter-gatherer way. These findings have produced searches for EXTERNAL forces [climate change in specific areas, population pressures] that PUSHED our ancestors into agriculture.

Thus, agriculture may be either a 'normal' cultural advance from the 'hunting/gathering' way of life (Sauer) or a 'forced' cultural change brought about by the need to increase carrying capacity (Mark Cohen) of the habitat, or a biologically-based 'co-evolutionary' interaction between domesticated plants and humans (David Rindos).  See overview

4. HOW?: 200 million years ago there were no Angiosperms - all flowering plants evolved and differentiated from a single ancestral line within the past 150 million years - a monophyletic lineage with some interaction from the insect world. 20 thousand years ago there were no domesticated plants - current array of domesticates represent organic evolution AND cultural evolution - NOT monophyletic - examples of CONVERGENT EVOLUTION, i.e., lineages moving from different wild ancestry to similar structural/physiological forms as domesticates.

WILD - ETHNOFLORA: CULTIVATED, WEED, PARTIALLY DOMESTICATED (GENETIC CHANGE), FULLY DOMESTICATED (DEPENDANT ON H. sapiens FOR SURVIVAL)

'WEED' DEFINED: CAN BE

a. 'NATIVE' COLONIZING SPECIES [LOCAL RAGWEED] OR [MORE COMMONLY] SPECIES THAT HAVE FOLLOWED H. SAPIENS [INTRODUCTIONS TO THE NORTH AMERICAN FLORA] - ARE SPECIES ADAPTED AND GENETICALLY SPECIALIZED TO OCCUPY HUMAN-CREATED ENVIRONMENTS [TARAXACUM IN LAWNS AND MANY WEEDS OF CULTIVATED FIELDS]

b. PLANTS WITH SOME GENETIC\PHYLETIC CONNECTION TO CROPS [JOHNSON GRASS - SORGHUM HALAPENSE - 'MILO' - SORGHUM BICOLOR - SOME OF THESE COMPANION WEEDS HAVE CLOSE CONNECTIONS TO THE ASSOCIATED CROP AND, PERHAPS, HAVE EVOLVED WITH THEM. LOCAL 'BIRD PEPPER' - Capsicum annuum is genetically compatible [same species or primary gene pool] as Jalapeno and Bell pepper.

Fully domesticated plants have EVOLVED by what is called 'artificial' selection [assumes man is un-natural], i.e. human selection. In some cases process can be seen clearly:

Seed crops [most important] - bell curve for germination dormancy in a typical annual - 'gathered' harvest of wild wheat would represent a population sample - local dispersal from processing - plants that would come up in the processing area would lack dormancy - these plants are the ones most likely to be taken 'in' to cultivation. Thus, lack of dormancy would logically be part of the 'cultivated' genome and the 1st step toward full domestication.

EDGAR ANDERSON - DUMP HEAP THEORY OF AGRICULTURAL ORIGINS

CARL SAUER - VEGETATIVE ['ROOT' PROPAGATED] CROPS FIRST - 'GATHERED' SEEDS FOUND THEIR WAY INTO 'ROOT' GARDEN PLOTS, GREW WELL [COLONIZING ANNUALS] AND WERE EVENTUALLY HARVESTED

How about non-shatter of the RACHIS? - possible reversal IF gatherers used 'beat into basket' method of harvest? Why.

THOSE WITH SHATTER WOULD GENERATE PROGENY TO BE TAKEN BACK TO THE VILLAGE - PROGENY OF 'NON-SHATTER' TYPES WOULD STAY IN THE WILD - SO, IN THIS CASE, HUMAN SELECTION IS ACTING TO MODIFY PLANTS THAT OCCUR IN THE WILD, NOT CULTIVATION, I.E. HUMAN SELECTION IS INDIRECT.

These different notions (Sauer - natural outgrowth of hunting-gathering vs. Harlan, !KUNG (result of external pressure) produce different perspectives concerning the origin and spread of agriculture:

Cultural/biological diffusion: few source localtities with subsequent extensive diffusion along pre-historic trade routes, vs.

Independent Invention/origin: many independent centers where agriculture developed as a result of similar pressures on many population centers.

5. WHERE?: Alphonse de Candolle - 1882 - Origins of Cultivated Plants - synthesis - mostly based on comparative botany - NIKOLAI VAVILOV - post-revolution interest in expanding the agricultural base (current result - Helianthus annuus) - world expeditions - centers defined on geographic patterns of genetic [domesticated landraces] and genomic [related wild types] variation - later work - genetics, archaeology, linguists, etc. - JACK HARLAN (Crop Evolution Lab - U. Illinois) has demonstrated 'secondary centers of variation' - diffusion of the crop THEN additional selection to produce new variants remote from the center of origin [ex. zucchini, pasta tomatoes].

1st Break = Old World vs. New World - major crop assemblages (starch - Poaceae and protein - Fabaceae)

Old World

Asia (mostly China) - Rice [Oryza sativa], Soybean [Glycine max]

Near East - Wheat or 'Corn' [Triticum aestivum and domesticted relatives], Lentil [Lens culinaris], Pea [Pisum sativum] - Cotton (Gossypium arboreum, G. herbaceum)

Africa - (mostly northern) Sorghum, Milo [Sorghum bicolor], Barley [Hordeum vulgare], Black-eyed Pea [Vigna unguiculata] and Bottle Gourd [Lagenaria siceraria] in sub-saharan Africa

New World

 (highlands of South Ameica and central Mexico with some activity in the Mississippi Valley) - Maize or 'Corn' [Zea mays], common beans (Phaseolus vulgaris) - Cotton - Gossypium hirsutum, G. barbadense


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15 Sep 2010