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Geographical Origins of Cultivated Plants (Gene Centres) and Atavisms

Gene centres are regions containing an extraordinary range of the wild counterparts of cultivated species, useful tropical plants or the geographic origins of non-cultured genera. A genetic set-back of a trait considered primitive in cultured varieties is called atavism.

The Russian geneticist N. I. VAVILOV (Moscow Agricultural Institute, Moscow - later he worked at Saratov, he died as a political prisenor) discovered in his numerous expeditions that certain geographic regions are characterized by an extraordinary range of wild varieties that can be regarded as the wild counterparts of cultivated species. He termed these regions main centers of the origin of cultivated plants or world centers of varietal diversity (genes) of cultivated plants.

The idea has been elaborated since then so that it refers now not only to the wild equivalents of world-wide cultivated plants but also to useful tropical plants as well as to the geographic origins of non-cultivated genera or families.

VAVILOV found similar changes or parallel mutations in many closely related species ("The Law of Homologous Series in hereditary Variation", 1920). Summarizing the results of his studies, VAVILOV came to the following conclusions:

1. Genetically closely related species and genera are characterized by similar series of hereditary variation with such a regularity that, knowing the series of forms within one species, one can predict the existence of parallel forms in other species and genera. The genetically closer the genera and Linnaeons within the general system are, the greater is the similarity in the series of their variation.

2. Whole plant families are generally characterized by a definite pattern of variation penetrating all the genera and species comprising a family.

All cereals, for example rye, wheat, millet, sago or maize have varieties with or without husks, such with stable or brittle ears or liguleless forms (wheat and rye). Ideal preconditions to generate combinations optimal for humans were thus given and the task remaining for man was only to select the most favourable varieties and to start their cultivation.

'Brittle ears' of gramineae is regarded as a primitive trait that occurs only exceptionally in cultivated varieties. The cross of certain varieties with stable ears results sometimes in offspring with brittle ears. Such set-backs are called atavisms (sing. atavism).

Important information (pictures, distribution, yield) about a number of cultivated plants can be found under:

World Centers of varietal diversity (genes) of cultivated plants

1. South-Asian tropical, including the following foci: (1.) Indian, (2.) Indo-Chinese, (3.) Insular, including the whole Malayan archipelago
2. East-Asian: (1.) Chinese, (2.) Japanese
3. South-West-Asian: (1.) Caucasian, (2.) Middle-East, (3.) Nort-West-Indian
4. Mediterraneae
5. Ethiopian: Adjacent to this is the mountainous Arabian, or Yemen, focus
6. Central American, including South Mexico. This is divided into (1.) Mountainous South Mexico, (2.) Centroamerican, (3.) West-Indian insular foci
7. Andian, within the South America. It includes (1.) Andian, (2.) Chiloanian or Araucanian, and (3.) Bogotan foci.

Some plants, VAVILOV wrote, have been introduced into culture from the wild flora in the past independent of the above enumerated seven main centers. Thus, in the oases of Arabia, South Mesopotamia, and maybe Sahara the date palm was introduced. In South Africa, in the regions adjacent to Kalahari desert, the water melon was introduced; within the inner tropical South America the manioc, ananas, peanut, and recently (by the Europaeans) the caoutchouc tree. In the North America, the Indians, still before Columbus, had introduced topinambour and sunflower.

Some plants of the old world, such as hemp, sorgo or apple-tree were introduced at different time and in different regions, so that it is impossible to localize their initial speciation and cultivation.