In VAVILOV (1951), there may arise a few questions: (1) Why does the same genus (or species) occur in more than one or even several centers of origin, although polyphyletic origins for certain cultivated plants are not postulated by him ? (2) How are we to interpret various expressions, for instance, "secondary centers of origin", "secondary center", "one of the centers of origin", "basic center", "one of the centers", and "a center", given for certain species? To quote ZOHARY (1970) again, "in many cases VAVILOV found centers of diversity for given crops very far away from the areas in which their wild relatives occur. A conspicuous case is the Ethiopian center. Here, wheats, barleys, peas, flax and lentils occur in an extraordinarily rich collection of varieties. Tetraploid wheats, for instance, manifested here according to Vavilov their widest variation. But significantly for all of these crops, they have not a single wild relative in Ethiopia. They therefore could not have possibly been domesticated there." I visited Ethiopia in 1964 and 1968, and I agree with ZOHARY'S interpretation. YAMASHITA et al. (1969) stated "any species of Aegilops, Secale and Agropyron, related to wheats, were not found, therefore durum wheats rich in variation is presumed not to be originated in Ethiopia or Abyssinian highland. They must have been introduced in ancient times and have yielded diverse variations there."
HARLAN proposed diffuse origins in his earlier papers (HARLAN, 1956, 1961, 1966): "Cultivated plants did not enter into domestication as the full blown crops we know today. They started as something much less impressive and more or less equivalent to their wild progenitors. Since, in some cases, we do not know the wild progenitors, we have only a general idea of what the earliest domesticates were like. We do have good evidence, in a number of instances, that the crops picked up additional germ plasm as they spread out of their nuclear areas of origination and came into contact with wild relatives." and "In wheat, we know that the heredity of Aegilops squarrosa was added to tetraploid wheat some time after domestication" (HARLAN, 1970).
Origin of Wheats
The genealogical relationships of the wheats have been established by KIHARA (1944) based on genome as well as morphological analyses, as follows:
In 1959, we were favored with an opportunity to visit the Agricultural Museum in Cairo, and to examine carbonated samples of disarticulated spikelets of wheat excavated from one of the oldest pyramids of Egypt estimated to be as old as about 7,000 years. They were identified by us to be T. dicoccum (4x). From the excavated material from Jarmo visited by BEM2) it has been also suggested that the origin of the 4x wheats can date back more than 7,000 years before the present.