PLB143 - Lecture 02:

Who's Who in the History of Crop Evolution Studies

C. Darwin (UK), A. de Candolle (CH), N. Vavilov (RU), J. Harlan (US)

© Paul Gepts 2015

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Presentation slides

Charles Darwin (1809-1882)


The Origin of Species by Means of Natural Selection or The Preservation of Favored Races in the Struggle for Life (1859)

  • Darwin's conundrum: "The laws of inheritance are quite unknown."
  • Evidence for selection and inheritance? Domesticated plants and animals: See his first chapter in the "The Origin of Species"

Higher levels of phenotypic variation (> than in wild plants)

  • "Comparing the diversity of flowers in the different varieties of the same species in the flower-garden; the diversity of leaves, pods, or tubers, or whatever part is valued in the kitchen-garden, in comparison with the flowers of the same varieties"
  • Examples:
    • Leaves: Lettuce (Lactuca sativa
  • Seeds:
    • Beans (Phaseolus vulgaris  
(compare with bean flowers:
    • Maize (Zea mays  
© National Geographic Society

Gigantism of harvested organs: e.g.,

(from B. Smith, The Emergence of Agriculture, © American Scientific Library 1995)

What is marsh elder (Iva annua)?

Increase in seed or fruit size as evidence for domestication in North American crops

Smith, B. D. 1992. Rivers of Change. Smithsonian Institution Press, Washington.




Increase in size can be due to a genetic cause, an environmental component, or both

Darwin suggested that the genetic component was larger than the environmental component
It’s Official! World Record Set At Port Elgin Pumpkinfest with 1,446 lb.
Today Oct 2 (2004) in PORT ELGIN…Port Elgin Pumpkinfest organizers are jumping for joy as a whopping 1,446 lb. new world record giant pumpkin was weighed in by grower Alan Eaton of Richmond, Ontario. Results have been finalized from the 23 other Great Pumpkin Commonwealth (GPC) sites confirming this new world record. Organizers will begin the process of having this pumpkin listed with Guinness as soon as possible. This must have been a good year for growing as 9 of the top pumpkins weighed in at Port Elgin were over 1,000 lbs. The previous World record for the pumpkin category was 1,385 lbs. held by Steve Daletas of Oregon.

“There will also be a discussion by the entire group regarding the genetics of the giant pumpkins and squash. The seed auction will be at the end of the seminar. There will be a seed raffle during the break.”



Domesticated types could not survive on their own!!

  • "Domesticated races show adaptation, not indeed to the animal's or plant's own good, but to man's use or fancy."
  • "Very many of the most strongly-marked domestic varieties could not possibly live in a wild state."

Mutually beneficial relationship between humans and their crops


What type of selection?

  • "... a kind of Selection, which may be called Unconscious, and which results from every one trying to possess and breed from the best individuals..."
  • "... breeders could never have expected or even have wished to have produced the result which ensued."
  • " a vast number of cases, we cannot recognize ... the wild parent-stocks of the plants which have been longest cultivated in our flower and kitchen-gardens."
  • "Man can hardly select, or only with much difficulty, any deviation of structure excepting such as is externally visible... He perceives extremely small differences, and it is human nature to value any novelty, however slight, in one's possession."
  • Conditions favoring selection:
    • High level of polymorphism
    • Large populations
    • High value
    • Ease in preventing crosses
  • Regions that have not contributed domesticated plants: e.g., Australia, Cape of Good Hope; due to absence of "civilization" according to Darwin


    • "In the case of most of our anciently domesticated animals and plants, I do not think it is possible to come to any definite conclusion, whether they have descended from one or several species."; i.e. which is the wild ancestor(s), single or multiple domestications, where?

Darwin and his Pigeons

A single origin for the domesticated pigeon (Columbia livia or rock-pigeon):

  • Only 1 likely ancestor on morphological grounds
  • Would have to postulate extinction of 7-8 species that would be necessary to explain current variation
  • Through crossing, it is possible to obtain progeny with ancestral traits
  • Hybrids among breeds have good viability and fertility
  • A few examples   of pigeon breeds known to Darwin (from his "The Variation of Animals and Plants under Domestication")

Some related sites of interest

Summary Darwin

By observing domesticated plants and animals, Darwin was able to demonstrate that selection could have major effects and that these effects were heritable (= transmissible to the progeny)
–No. 1: more variation in shape, color of harvested organs compared to non-harvested
–No. 2: increased size of harvested organs
–No. 3: importance of the genetic component of variation
–No. 4: could not survive without the assistance of humans
–No. 5: extreme differences à unconscious selection
–No. 6: attracted by novelty
–No. 7: practical experiments with pigeons

Alphonse de Candolle (1806-1893)

Origin of Cultivated Plants (1883)

  • Reasoned Geographical Botany (1855):
    • "Conditions anterior to our epoch determined the greater number of the facts of the actual distribution of plants ..."

  • "So far as cultivated plants are concerned, the questions which occur do not make it necessary to go back to very ancient times ... Cultivation began after this epoch [last glaciation] and even in many instances in historic times ... This is a great simplification."

Some related sites of interest

Contributions of  de Candolle, the father of the study of crop evolution

What type of evidence can we use to determine the origin of a crop?

  • Botanical
  • Archaeological
  • Historical
  • Linguistic

Botanical Evidence

  • "... to seek in what country it grows spontaneously and without the help of man."
  • Caveats:
    • incomplete records
    • introduced but short-lived
    • naturalized species

  • How do you recognize a wild form related to a crop? "... a cultivated species varies chiefly in those parts for which it is cultivated ... We may expect, therefore, to find the fruit of a wild fruit tree small and of a doubtfully agreeable flavour, the grain of a cereal in its wild state small, the tubercles of a wild potato small, the leaves of indigenous tobacco narrow, etc."
  • Problem: "... we still have to decide what group of nearly similar plants it is proper to designate as constituting a species ... ":
  • Example: What is a bean? Different bean types (from The Wellness Encyclopedia of Food Nutrition, 1992, © Health Letter Associates)

Archaeological Evidence

  • "... The most direct proof which can be conceived of the ancient existence of a species in a given country is to see its recognizable fragments in deposits, of a more or less certain date."
  • Examples given by de Candolle:
  • Other examples:
    • architectural motifs: date palm , grapes and pomegranate (Punicum granatum), grapevine (both coins and architectural motifs from " Plants and Judaism " of the Botany Dept. at the University of Tel-Aviv)
    • ceramics: lima bean (Phaseolus lunatus) and oca (Oxalis tuberosa) in Peru (compare the latter to the " real thing ") (oca ceramic: from Seeds of Change, © Smithsonian Institution 1991)

Some related sites of interest

  • Tumuli and mounds of North  America (from B. Smith, The Emergence of Agriculture, © Scientific American Library 1995)
  • Ancient Egyptian tombs
    • Abu Simbel:
       Abu Simbel
    • Pyramids of Giza:
    • Mural:
  • coins (e.g., Near East ), architectural motifs (e.g., Near East ), ceramics (Andes), etc.

Historical Evidence

  • Historical records, ancient manuscripts or herbalsHerbal of Dodoens
  • a drawing of common bean
herbal bean

Caveats against historical evidence:

  • Confusion between crop and wild ancestor
  • Confusion between countries of origin and of introduction
  • Forgeries
  • Translation of plant names
  • Botanical expertise

Linguistic Evidence

  • Names designating crops, especially in native languages
  • Many unreliable cases
  • Nevertheless, can be used with caution

Example of linguistic evidence: Crops of the Andes

Crop type Latin binomial English Spanish Quechua (language of the Incas)
Cereals Zea mays maize, corn maíz sara
Pseudo-cereals Chenopodium quinoa quinoa quinua kiuña
Chenopodium pallidicaule
cañahua qanawi
Amaranthus caudatus amaranth achita achita, achis, coimi, okiru, quihuicha
Legumes Phaseolus vulgaris common bean frijol, poroto purutu
Canavalia ensiformis jack bean

Arachis hypogea peanut, groundnut maní inchis
Lupinus mutabilis lupin chocho tarwi
Tuber-bearing plants Xantoma spp.
unchuca uncucha
Canna edulis
achira achira
jíquama ajipa
Oxalis tuberosa
oca oqa
Tropaeolum tuberosum
mashua allausu, añu
Arracacia xanthorhizus
arracacha raccacha
Manihot esculenta cassava yuca ruma
Solanum spp. potato papa apichu, kumara
Ullucus tuberosus
ullucu, papalisa ulluku
Polymnia sonchif
yacón yakon, yakuma
Stimulant Erythroxylon coca coca coca coca, cuca


Andean crops

Quinoa (Chenopodium quinoa)

© Paul Gepts

Amaranth (Amaranthus caudatus)

© Cristina Mapes

Tarwi or chocho (Lupinus mutabilis)

© Paul Gepts

Coca (Erythroxylon coca)

from rus_bio/Rusmidlernes_biologi-8.htm


Arracacha (Arracaccia xanthorrhiza

from  Steen Randers Knudsen, FAO, and CIP

Achira (Canna edulis)

Mashua, añu (Tropaeolum tuberosum)

Cassava, yuca (Manihot esculentum)

Nicolai I. Vavilov (1887-1943)

Studies on the Origin of Cultivated Plants (1926)

  • Established a very active program of study of crop diversity in what is now the Vavilov Institute of Plant Industry in St. Petersburg (Leningrad at that time)).

  • Plant materials were obtained in part by extensive germplasm explorations in many parts of the world.
  • "In spite of the internationalization of cultivated crops and in spite of all the human migrations and colonizations as well as the very antiquity of agriculture, it is still possible ... to establish regions of endemic varieties and races, to discover regions where the maximum primary variation of strains occurred and to establish a number of regularities concerning the distribution of inherited characteristics."
    • (1) Determine the geographic distribution of morphological and physiological variation
    • (2) Identify regions with maximum diversity


Itinerary of Vavilov in North America and Mexico

Vavilov trip in N. Am, Mexico

Vavilov's "differentiating, taxonomical-geographical method" for determining centers of crop origin

  • Differentiate a plant into Linnean species
  • Determine the geographic distribution areas of these species
  • Determine in detail the composition of the varieties and races of each species and the inheritance of genetic variability
  • Establish the geographic distribution of inherited variation and determine the geographic center of accumulation of varieties
"The region of maximum variation, usually including a number of endemic forms and characteristics as well, can usually, be considered as the center of type-formation."
Vavilov centers The seven centers recognized by Vavilov

Additional Statements by Vavilov

  • "... there is no doubt that the wild forms, ancestral to the presently cultivated species, deserve the same research efforts as given the cultivated species."
  • "When related to a definite, botanical point of view, [data from archaeology, history, and linguistics] can often ... supplement and enhance information about the past of cultivated plants."
  • The center of origin of a cultivated plant is often correlated with the center of origin of associated pathogens.
  • It is necessary to distinguish primary and secondary centers of diversity.

Some sites of interest

Jack R. Harlan (1917-1998)

Sites of interest

A biography and list of writings of  J. Harlan , requires Acrobat Reader


Evidence for Origin and Dispersal of Cultivated Plants (Harlan and de Wet 1973)

  • Plants
    • Living:
      • Experimental taxonomy
      • Geographic distribution
      • Ecological behavior
      • Genetic systems
      • Variation patterns
      • Morphology
      • Genetic reconstruction
    • Dead:
      • Archaeology
      • Palynology
      • Paleobotany

  • Humans
    • Living:
      • Language
      • Oral tradition
      • Techniques
      • Attitudes towards the crop
      • Nutrition
    • Dead:
      • History
      • Art
      • Archaeology
      • Physical anthropology

Evaluation of the Evidence on the Origin of Crops

  • Evidence x Qualification => Level of confidence
  • Qualification:
    • Authenticity
    • Abundance
    • Kind
    • Interpretation
    • Integration

PLB143: Questions - Lecture 02

  • What are the different issues raised by these four great scientists with regard to crop evolution and its study?
  • What are the advantages and disadvantages of using crop evolution as an experimental system for evolution in general?

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