Corn inbreeding

​Development of corn from a wild species of Teosinte was a remarkable human endeavor.  Along the way it depended upon mutations allowing people to select more desirable types. As it was moved to multiple environments over nearly 10000-year history, varieties were selected by locals to best fit their environmental and cultural preferences.  Open pollination, because of separation of male and female flower structures, encouraged continual mixing of genetics within a variety as well as occasional mixing of varieties. Mixing of varieties, sometimes by accident as in the case of the Northern flint with the Southern dent in the case of Reid farms resulted in new vigor to the next generation.
 
Open pollination had allowed for variability and, therefore, adaptation to many environments but it also more or less capped the yield, as there would remain individual plants that were genetically inferior sometimes from concentration of negative recessive genes. The challenge was how to take advantage of the variability and yet obtain the uniformly superior, adapted plants.
 
Concurrently, plant researchers studying the principle of heterosis, in which crosses between unrelated species or subspecies showed vigor were showing interest in this phenomenon in corn.  George Shull in 1908, at Cold Spring Harbor invented the term heterosis for the increased vigor that results when unrelated varieties are crossed.  This became especially clear when corn was selfed sufficiently to become inbreds, resulting in puny plants with small ears and then crossed with other inbreds to create hybrid plants.  Other university plant researchers in the early 1900’s were experimenting with inbreeding to obtain more genetic uniformity but struggling with the reduced plant size of inbreds.