Centres of Origin or Diversity

Vavilov started off with five original centres for the origin of cultivated crops, later expanding this to seven and then eight. P.M. Zhukovsky then expanded the number of centres to 12, bringing in Australia and New Zealand, Siberia and North America and modifying Vavilov’s original centres somewhat. Later plant geographers modified the original concept even further, arguing that within a much smaller number of centres of origin, for agriculture as a whole, there are many more centres of diversity, for particular crops. This idea is most closely associated with Jack Harlan, whose father, Harry Harlan, had been good friends with Vavilov. Jack Harlan identified three centres, and three non-centres.

“I propose the theory that agriculture originated independently in three different areas and that, in each case, there was a system composed of a center of origin and a noncenter, in which activities of domestication were dispersed over a span of 5,000 to 10,000 kilometers. One system includes a definable Near East center and a noncenter in Africa; another system includes a North Chinese center and a noncenter in Southeast Asia and the South Pacific; the third system includes a Mesoamerican center and a South American noncenter. There are suggestions that, in each case, the center and noncenter interact with each other. Crops did not necessarily originate in centers (in any conventional concept of the term), nor did agriculture necessarily develop in a geographical center.” ^[1]

Harlan went on to classify crops into five different classes:

• Endemic crops, such as the bitter potatoes of the Andes, have their origin in a limited area and have not spread beyond that area.
• Semi-endemic crops have had some dispersal beyond their area of origin. Harlan cites tef (Eragrostis tef) in Ethiopia and Oca (Oxalis tuberosa) in the Andes, but many of these are now spreading further afield as farmers experiment with an increased range of agricultural biodiversity.
• Monocentric crops have a definable center of origin and widespread dispersal, but no secondary centres of diversity. Paul Gepts says these are mainly relatively new orchard and plantation crops, such as rubber, coffee and mango.
• Oligocentric crops have a defined centre of origin and wide dispersal, and in that dispersal have given rise to one or more secondary centres of diversity. These are the classic crops of agriculture, such as wheat, barley and chickpeas, originating in the near east and with secondary centres in Ethiopia and India.
• Noncentric crops were domesticated over a wide area and do not apparently have centres of diversity. Sorgum, present along with its wild relative over the whole of sub-Saharan Africa, is an example.

New techniques of analysis, from microscopic examination of archaeological remains to wide surveys of crop DNA, continue to shine new light onto the origins, domestication and diversity of crops that change, sometimes in important ways, our understanding of the history of agriculture. Nevertheless, Vavilov’s original insights into the likely centres of origin and diversity remain important today and continue to guide the collection, study and use of cultivated plants.

1. Harlan, J.R. 1971. Agricultural origins: Centers and noncenters. Science 174: 468-474. [↩]