Origin, Adaptation, and Types of Corn

May 1985 ORIGIN OF CORN Corn (Zea mays L.) is the only important cereal indigenous to the Western Hemisphere. Apparently originating in Mexico, it spread northward to Canada and southward to Argentina. While the possibility of secondary centers of origin in South America cannot be completely ruled out, the oldest (7000 years) archaeological corn was found in Mexico’s Valley of Tehuacan. The earliest “corn” of which there is record is unmistakably corn. The female infl orescence of this 5000 B.C. corn had reached a degree of specialization that precluded the possibility of natural seed dissemination. Thus, the oldest corn of record was dependent upon man for its survival. Numerous theories of origin have been offered over the years, only two of which receive serious consideration today. One is that teosinte (Zea mexicana) is the wild progenitor of corn; the other is that a wild pod corn, now extinct, was the ancestor of domesticated corn. While perhaps more students of corn seem to accept the fi rst theory, others are equally convinced of the second. Aside from its possible role in the origin of corn, teosinte has had major impact on its evolution. In Mexico particularly, introgression between corn and teosinte has likely occurred for centuries and continues to this day. The effects are apparent in the morphology and cytology of both species. There is also reason to believe that genes for resistance to certain viruses have reached corn through its introgression with teosinte. The origin of corn may never be known with certainty. One reason is that the hypotheses purporting to explain origin cannot be tested experimentally. Therefore, science would perhaps be better served if less attention were given to determining corn’s origin and more to understanding the remarkable variability found within the species.